Lecture 1 and part
of lecture 2 notes
Hint: when printing choose
pages per sheet and print out 2 or 4 pages per sheet of paper!
Expected
Learning Outcomes:
It
is expected that a student completing this class should be able to understand:
1. plant structure and its relationship to plant
physiology
2. transport of water, nutrients and
carbohydrates throughout the plant
3. photosynthetic and respiratory pathways in
plants
4. hormonal regulation of plant function
5.
plant physiological response to environmental stress
Methods
of Assessing Expected Learning Outcomes:
1. In the lecture, learning outcomes will
be assessed by the administration of weekly quizzes and two exams .
2. In the laboratory, learning outcomes
will be assessed by reviewing lab reports and
a lab final.
II.
What is Plant?
A. Definition - by most definitions, a plant:
is
multicellular;
is non-motile
has
eukaryotic cells
has cell
walls comprised of cellulose
is
autotrophic; and
exhibits
alternation of generations - has a distinctive diploid (sporophyte) and haploid
(gametophyte) phase.
B.
Examples - the Plant Kingdom includes the angiosperms (flowering plants), gymnosperms
(cone-bearing plants), ferns, and bryophytes (mosses & liverworts). Recent
classification systems suggest that these organisms, in addition to the red
algae and green algae, should be classified in the Plant Kingdom (Plantae).
III.
What is Plant Physiology?
A.
Definitions (numerous) - Plant physiology is the study of:
the functions
and processes occurring in plants
the vital
processes occurring in plants
how plants
work
B. In
essence, plant physiology is a study of the plant
way of life, which include various aspects of the
plant lifestyle and survival including: metabolism, water relations, mineral
nutrition, development, movement, irritability (response to the environment),
organization, growth, and transport processes.
C.
Plant physiology is a lab science.
D.
Plant physiology is an experimental science.
E.
Plant physiology relies heavily on chemistry and physics.
IV. Why Study
Plant physiology?
Food - plants
are the route by which solar energy enters ecosystems
Economically
important products - plants produce countless products from fibers to medicines
to wood. For example, you can check out the web notes for my Plants
and Human Affairs course or The
Society for Economic Botany
Applications
to other disciplines (i.e., agriculture, forestry, horticulture)
Theoretical
importance (like a mountain - its there!)
V. The
Literature of Plant Physiology
There is an incredible wealth of information about plant
physiology. Never say, "nothing is known about...." unless you are
positive. Chances are someone, somewhere, sometime, has studied the phenomena.
I think it was Bertrand Russell who said something like, "its easier to
make a scientific discovery than to discover if its already been
discovered". Since, theres so much literature available, it pays to learn
a little about the types of resources that are available.
One reason why there is so much information is that plant physiology material
is found in both the biological and chemical literature.
A.
Types of literature
Primary -
original reports of research; journals.
Two excellent journals that are published by the American Society of Plant Biology
are Plant Physiology
and Plant Cell,
both of which are available in the Clemens Library. Well check out a
copy of Plant Physiology and point out volume, number, date of
publication, publisher, organization, format, etc.
The
American Society of Plant Biologists has developed the following Principles
of Plant Biology to provide basic plant biology concepts for science
education at the K-12 levels and to help students gain a better understanding
of plant biology.
Plants contain the same biological
processes and biochemistry as microbes and animals. However, plants are unique
in that they have the ability to use energy from sunlight along with other
chemical elements for growth. This process of photosynthesis provides the
world's supply of food and energy.
Plants require certain inorganic elements
for growth and play an essential role in the circulation of these nutrients
within the biosphere.
Land plants evolved from ocean-dwelling,
algae-like ancestors, and plants have played a role in the evolution of life,
including the addition of oxygen and ozone to the atmosphere.
Reproduction in flowering plants takes
place sexually, resulting in the production of a seed. Reproduction can also
occur via asexual propagation.
Plants, like animals and many microbes,
respire and utilize energy to grow and reproduce.
Cell walls provide structural support for
the plant and also provide fibers and building materials for humans, insects,
birds and many other organisms.
Plants exhibit diversity in size and
shape ranging from single cells to gigantic trees.
Plants are a primary source of fiber,
medicines, and countless other important products in everyday use.
Plants, like animals, are subject to
injury and death due to infectious diseases caused by microorganisms. Plants
have unique ways to defend themselves against pest and diseases.
Water is the major molecule present in
plant cells and organs. In addition to an essential role in plant structure,
development, and growth, water can be important for the internal circulation of
organic molecules and salts.
Plant growth and development are under
the control of hormones and can be affected by external signals such as light,
gravity, touch, or environmental stresses.
Plants live and adapt to a wide variety
of environments. Plants provide diverse habitats for birds, beneficial insects,
and other wildlife in ecosystems.
Why
a class in physiology?!
Once you receive your degree in plants, for the rest of your life you will be
asked questions about how plants work. In your professional work with plants --
whether you become a garden curator, golf course superintendent, nursery
manager, landscape designer, horticultural writer -- knowing what makes plants
tick will help you be better at your job.
For these
reasons, we have developed a course in plant functioning, oriented to the
garden/landscape.
"Understanding how
the whole factory operates and how it uses its raw materials allows us better
to control the end product more effectively. By knowing the way in which
a leaf works, for example, you'll realize just how important it is to supply a
plant with the conditions it needs. Learning the internal mechanisms of a
plant will give you a whole new insight into traditional gardening
techniques."
First
paragraph of the class text book, Digging Deeper: Understanding How Your Garden
Works
Why is
important and interesting to study plant physiology?
Why is this
course important in our curriculum and what is the justification for our
society funding research on plant science? (greater than $400 million dollars a
year in Federal money)
1)Plants are
the ultimate food source for what we eat
Trace the
number of the world's population-
very low when
primarily hunters (migratory, couldn't travel with very many kids)
started
rapidly growing upon the switch to agrarian society (~10,000 years ago)
=permanent
home, stored seeds, increasing vegetable component of diet
kids more of an asset in agrarian society
need less land than for hunting, can have cities
~5 million people 10,000 years ago
now is
growing at 1.5% per year (may level off at 10-14 billion by 2100??)
2) Plants
produce the oxygen we breathe and consume CO2 we produce
Interaction between
global vegetation and the composition of the atmosphere
atmosphere is
~0.035% CO2 now, predicted to increase to 0.06% by 2050
plants are
also sensitive to air pollution
3) Plants are
sources of many non-food products we need
Fiber=shelter,
clothing, paper
Medicines
Energy-
renewable
Oils
4) Natural
curiosity
Plant
biochemistry and physiology is different from animals/bacteria
Plants are
sessile
must endure
the climate
grow
indeterminately to compete successfully
must obtain
nutrition from their immediate surroundings
dispersal/breeding
strategies have evolved
must defend
themselves-can't run & hide
What are some
of the objectives of current research in plant science?
Increased
yield of currently cultivated crops
Need to
increase yield to better feed the world population (>5.8 billion)
we have made
big increases in crop production over the past 30 years and mostly due to
increased yield=green revolution
yield is
often proportional to input-more fertilizer, water, pesticide
=fossil fuel
products, very expensive
yield
increases in cereals-wheat and rice due to breeding; corn due to hybrid vigor
=2.6-fold
increase in world grain production since 1950 (loss of >20% of topsoil on
cultivated land)
but...in much of the developing world >75% of the population is engaged
in food production in the U.S. in recent decades <3% of the
population produce our food
better or
faster production and allocation of photosynthate
better
resistance to diseases and pests-before and after harvest (using less
pesticide)
greater
tolerance to stress-drought, salt, pollution, heat, cold
better
agricultural technique-control of weeds, ripening, growth (sustainable)
engineering
of nitrogen fixation
Improved
qualities
more
nutritious foods and feeds=better balance of essential amino acids
ag products
that require less processing
products that
yield less waste by-products
New plants
developed as cultivatable crops
we currently
derive 80% of our calories from only 6 different angiosperms (out of
235,000)-only 3,000 have ever been cultivated for food, only 150 ever widely
cultivated
New products
from plants
(Using the
ability of plants to harvest solar energy for new applications)
There has
been an attitude that purification of products from plants is archaic compared
to chemical synthesis in production laboratories
Plant
products as substitutes for fossil fuels
industrial
oils
energy
production
auto fuel
biodegradable
plastics
natural
rubber
Plant
products which are medicines or using plants to produce medicines
vaccines in
plants-i.e. oral vaccines in bananas to hepatitis B, rotavirus
Plants in
bioremediation
cleaning up
contaminated soils-heavy metals
using plants
to treat/clean industrial waste
Impact of
ecosystem disturbance on plants
loss of
biodiversity
shifts in
competitive advantage
effects of
changes in atmosphere
Plants in
space
I. What is
Plant Physiology?
-sum of all
processes and structures that contribute to the life of a plant
-plant
physiology is interdisciplinary and is rapidly advancing
-relationship
between structure and function is essential
-plants are
dynamic organisms
II. What is a
plant?
-algae, lower
and higher plants - continuous variations on a theme
-our focus
will primarily be on the angiosperms (higher flowering plants)
III. What are
plants made up of?
-plant cells
are the fundamental unit of life
-cells
contain proteins, nucleic acids, lipids, carbohydrates, and many other things
Plasma
membrane
-lipid
bilayer in which phospholipids predominate
-highly
fluid, impermeable to most polar molecules
-contains
many proteins (both integral or peripheral) involved in structure and transport
Vacuoles -
unique to plants
-large
internal vesicle (>90% of cell volume) surrounded by tonoplast
-multiple
functions- maintains turgor pressure, shape of cytoplasm, storage, regulation
of cytoplasm
A. Plasma or Cell
membrane
Cell boundary; selectively permeable; bilayer of
phospholipids with inserted protein. Phospholipids are unique molecules - they
are amphipathic, meaning that they have both hydrophilic and hydrophobic
regions. They have a glycerol backbone; one of the hydroxyls is bonded to
a phosphate and another charged group, the other two hydroxyls are esterified
to fatty acids. The fatty acids range in length from C14 - C24. One
fatty acid is usually unsaturated and the other is saturated.
The unsaturated fatty acid is kinked
which helps to keep plant cell membranes fluid at cool temperatures. As a
result plant phospholipids usually have a higher degree of unsaturation than
animals. Hydrophobic interactions between the tail regions of the
phospholipids hold the membrane together. Some proteins are found: (1) just on
the outside or inside surfaces of the membrane (peripheral proteins -
non-covalent interactions and anchored proteins - covalently bound to lipids,
etc); or (2) embedded in the membrane (integral protein), many of which span
the membrane (trans-membrane proteins).
Hydrophilic regions of the integral
proteins are oriented to the outside of the membrane whereas hydrophobic
regions are embedded within the phospholipid bilayer. Lipid soluble
materials can readily pass through but charged or ionized substances
(hydrophilic) pass through very slowly, if at all. The function of the membrane
is to: (1) regulate traffic; (2) separate the internal from external
environment; (3) serve as a platform on which some reactions can occur; (4)
participate in some reactions (i.e., the membrane components are
important intermediates or enzymes); and (5) provide some structural integrity
for the cell.
. A typical plant cell
has an external Wall, Cytoplasm and a Vacuole. The Plasmalemma is the boundary
that separates the Cytoplasm and the Wall. The Tonoplast (Vacuole Membrane) is
the boundary between the Vacuole and the Cytoplasm.
. If all of the
Protoplasts are destroyed, the Apoplast remains like a honey-comb. The Apoplast
consists of the Cell Walls and Intercellular Spaces.
This image shows the thick and sturdy cell walls found in the Velamen of
Orchids. The Protoplasts are gone and the Apoplast is all that remains. The
Velamen is the white part of exposed orchid roots.
. When the Cell Wall
is removed, the Protoplast is directly exposed to the outside emvironment. The
Protoplast is the Plasmalemma and everything in side of it.
. If all of the Cell
Walls were removed and the cells touched one another they would constitute a
Symplast (Sym means together).
. Cells are
interconnedcted by Plasmodesmata. The interconnected Protoplasts constitute the
Symplast.
Building
Blocks: Lipids, Proteins and Carbohydrates
Alcoholsan
alkane with a hydroxyl group added – hydroxyl group of alcohols is
hydrophilic (water-loving) attracts water. Makes it a good organic solvent
CH3-0H
The
main alcohol you need to be aware of today is
CH3CH2CH2OHor
Propanol that has 3 OHs--Glycerol
H
|
-C- H
|
OH
Figure 5.12
Examples of saturated and unsaturated fats and fatty acids
Lipids contain
• Fatty acid
molecule and glycerol hydroxyl
combined with ester
linkage
– saturated fat = no
double bonds
– unsaturated fat =
double bonds kinks chain
Fatty Acid Molecule –
Complex
lipids
•
phospholipids
–
glycerol
–
two fatty acids
–
phosphate group
Phospholipids continued
• Phosphate group
give lipid a polar head.
– (hydrophilic water
loving)
• Fatty acids are
hydophobic (water-fearing).
• In water
phospholipids form a bilayer = membrane polar group facing out, fatty acids in.
Lipids
and Water
Fatty
acids have a hydrophobic tail
Causes
them to form a film on water or, a sealed sphere (a micelle)
+
hydrophilic head
Hydrophilic and Hydrophobic Substances
A
hydrophilic substance
Has
an affinity for water
A
hydrophobic substance
Does
not have an affinity for water
Figure 5.14
Bilayer structure formed by self-assembly of phospholipids in an aqueous
environment
Table 5.1 An
Overview of Protein Functions
Proteins
• Proteins are
essential for all aspects of cell structure and function.
– Enzymes
• Building block
proteins = amino acids
Figure 5.18 Making a polypeptide chain
Amino Acids
• contains at least
one Carboxyl group
• contains at least
one Amino group
• Off of the alpha
carbon
– R = attached
groups containing carbon, hydrogen, oxygen, nitrogen and some cases sulfur.
– there are 20
different amino acids
Peptide Bonds
• It is another
dehydration synthesis
– two amino acids =
dipeptide
– three amino acid =
tripeptide
– long, chain =
polypeptide
• folded functional
polypeptide = proteinFig. 2.8
Levels of Protein
Structure:
• primary structure
= unique sequence of amino acids linked together.
• secondary
structure = twisting and folding of
polypeptide chain (helix and/or pleated sheets.
Figure 5.20 Exploring Levels of Protein Structure: Primary
structure
Figure 5.20 Exploring Levels of Protein Structure:
Secondary structure
Figure 5.20 Exploring Levels of Protein Structure:
Tertiary structure
Protein Tertiary and
Quaternary Structure
Nucleic Acids
• RNA and DNA are
polynucleotides
Figure 5.20 Exploring Levels of Protein Structure: Quaternary
Structure
Figure 5.22 Denaturation and renaturation of a protein
Carbohydrates
• Sugars and
starches
• made up:
– carbon
– hydrogen
– oxygen
• C6H12O6=
glucose
• general formula -
(CH2O)n
Carbohydrates continued
• monosaccharides (
sacchar = sugar)
– 4 carbons =
tetrose
– 5 carbons =
pentoses
– 6 carbons =
hexoses
• glucose is a
hexose important living organisms.
– 7 carbons =
heptoses
Carbohydrates continued
• disaccharides ( di
= two)
– two monomers
formed by dehydration synthesis reaction.
• sucrose = glucose
and fructose
• lactose = glucose
and galactose
• polysaccharides
• 10 to 100
monosaccharides joined through dehydration synthesis
Monosaccharides
(sugars)
Generic
formula of -(CH2O)n
-
where 3<n<8, with >2 -OH groups
Terminal
aldehyde group (aldoses) or ketone group (ketoses)
•
monosaccharides ( sacchar = sugar)
–
4 carbons = tetrose
–
5 carbons = pentoses
–
6 carbons = hexoses
•
glucose is a hexose important in living organisms.
–
7 carbons = heptoses
Monosaccharide
Ring Formation
In
aqueous solution aldehyde or ketone group reacts with the -OH group to close
the chain into a ring structure
Minor
differences in the spatial arrangement of atoms leads to the formation of
isomers.
e.g.
Glucose, mannose and galactose have identical formulas (C6H12O6) but different structures
Allows
for specific enzyme recognition and different biological effects
Sugar
derivatives
Hydroxyl
group of simple monosacharides can be replaced
Alters
the physical properties of the molecule and how it reacts
Figure 5.7 Starch
and cellulose structures
Figure 5.8 The arrangement of cellulose in plant cell walls
Disaccharide Formation
Hydroxyl group on the
carbon that attaches to the ketone or aldehyde group
can change position
a-hydroxyl down
hydroxyl up
Also allows one
monosaccharide to react with another -OH group
Forms a disaccharide
-4 Linkage
Disaccharide
and Polysaccharide
Formation
The
disaccharide formed depends on the type of monosaccharide involved
Glucose
+ Glucose = Maltose
Glucose
+ Galactose = Lactose
Glucose
+ Fructose = Sucrose
Figure 5.5
Examples of disaccharide synthesis
Polysaccharides
are formed by multiple monosaccharides joining together in repeating units
(e.g. Glycogen is a polysaccharide made of glucose)
Complex
polysaccharides are formed by multiple different monosaccharides joining
together in repeating units.
Complex
polysaccharides are often linked to proteins or lipids
Figure 5.6 Storage polysaccharides of plants and animals
Communication Between Cells
Fluids
and dissolved substances can pass through primary walls of adjacent cells via
plasmodesmota.
Cytoplasmic
strands extending between cells.
Cellular Components
Plasma
Membrane
Composed
of phospholipids arranged in two layers, with proteins interspersed throughout.
Some
proteins extend across the entire width, while others and embedded to the outer
surface.
Microbodies
Microbodies
are small, spherical bodies with a single membrane, distributed throughout the
cytoplasm which contain specialized enzymes.
Perixosomes
- Serve in photorespiration.
Glyoxisomes
- Aid in converting fat to carbohydrates.
Nucleus
Nucleus
is bound by two membranes, which together constitute the nuclear envelope.
Structurally
complex pores occupy up to one-third of the total surface area.
Contains
fluid nucleoplasm packed with short fibers, and contain larger bodies.
Nucleoi
composed primarily of RNA.
Chromatin
Strands - Coil and become chromosomes.
B. Nucleus
The cell "brain". Surrounded by a double membrane
(two phospholipid bilayers) - the nuclear membrane. Has pores. The
structure of the pores is complex comprised of a more than 100 proteins.
The pore opening is surrounding by a series of proteins and these are attached
to a series radial spokes. Nucleoplasm - matrix within nucleus. DNA,
which is found in the nucleus, may be condensed into chromosomes or not
(chromatin). There may be one or more nucleolus (site of ribosome production).
The nucleus is 5-20 mm
in diameter. There is a layer of intermediate filaments (see below) just
inside the nuclear envelope; called the nuclear lamina.
C. Cytoplasm/cytosol
The cytosol is the gel-like matrix within the cell in which
the other structures are embedded. The cytoplasm refers to the cell
materials inside the membrane.
Ribosomes
Ribosomes
are composed of two subunits composed of RNA and proteins.
Ribosomal
subunits are assembled within the nucleolus, released, and in association with
special RNA molecules, initiate protein synthesis.
Have
no bounding membranes.
Endoplasmic Reticulum
Endoplasmic
Reticulum facilitates cellular communication and materials channeling.
Enclosed
space consisting of a network of flattened sacs and tubes forming channels
throughout the cytoplasm.
Ribosomes
may be distributed on outer surface (Rough ER).
Associated
with protein synthesis.
Smooth
ER is devoid of ribosomes and is associated with lipid secretion.
F. Endoplasmic reticulum
A series of membranous tubes and sacs (cisternae) that run
throughout the cell. Rough ER has ribosomes associated with it and is laminar
while smooth ER lacks ribosomes and is tubular. Totally man. The ER
has several functions including: (1) synthesis of lipids and
membranes (smooth ER); (2) serving as a site for the synthesis of proteins by
the ribosomes (rough ER); (3) transport (a type of cell 'highway' system); and
(4) support.
. a) formation of vesicles to transport
membrane and contents of lumen; vesicles bud off ---> Golgi
b) modified in special cells for various
functions - e.g. sarcoplasmic reticulum in muscle cells.
c) lipid synthesis
d) drug detoxification
2. Endoplasmic Reticulum: --double
membrane continuous with nuclear membraneΛER lumen separated from cytosol
Rough ER contains bound ribosomes
Smooth ER no ribosomes
Dictysomes
Dictysomes
(Golgi Bodies in animals) are often bound by branching tubules that originate
from the ER.
Involved
in the modification of carbohydrates attached to proteins synthesized and
packaged in the ER.
Polysaccharides
are assembled within dictysomes, and collect in small vesicles.
Migrate
to plasma membrane and secrete contents to the outside.
Golgi Appratus
3. Golgi Apparatus
communicates with ER via transport
vesicles that bring membrane and proteins synthesized in ER
Golgi modifies lipids and proteins and
sends them on
4. Lysosomes - digest macromolecules
using enzymes transported from Golgia via transport vesicles
C. Golgi Complex ...
1. Intermediate step for vesicles
produced by smooth ER transporting membrane and proteins
a) flattened discs of stacked membranes
enclosing a lumen
b) cis face - end of Golgi where vesicles
arrive; very close to or in contact with ER
c) trans face - opposite end from forming
face; where processed vesicles are leaving
2. Golgi modifies products of ER
.
Mitochondria
Mitochondria
release energy produced from cellular respiration.
Inward
membrane forms numerous folds (cristae).
Increase
surface area available to enzymes in the matrix fluid.
D. Mitochondria
These organelles, like the nucleus and plastids, are
double-membrane bound. They vary in shape from tubular (like sausages) to
spherical. They reproduce by fission, have their own ribosomes and DNA (a
circular loop like prokaryotic cells). The inner membrane has a larger surface
area so it must be folded into finger-like projections (called cristae) to fit
inside the outer membrane. Mitochondria are found in all eukaryotic cells. They
are the sites of cellular respiration - process by which energy is released
from fuels such as sugar.
The mitochondria are the power plant of
the cell. They are small (1-5 mm) and
generally numerous (500-2000 per cell). A popular misconception is that
"plants have chloroplasts, animals have mitochondria." Plant cells,
at least green plant cells (i.e., leaf cells), have both. Root
cells only have mitochondria. Mitochondrial DNA which comprises about 200
kbases, codes for some of the genes required for cellular respiration including
the 70S ribosomes and components of the electron transport system. The inner
membrane differs from the plasma membrane in that it has a higher protein
content (70%) and unique phospholipids (i.e., cardiolipin).
Mitochondria
. B. Mitochondria ... 1. Cellular
Respiration -- oxidize intermediate products of metabolism to CO2 and H2O;
excess free energy transformed into synthesis of ATP
2. Structure
a) Approximately 1 ΅ in diameter; may be
very long in some cells
b) 2 membranes - inner membrane and outer
membrane
c) inner membrane has large surface area
and folds inward forming cristae; contains membrane proteins responsible for
respiration and ATP synthesis
d) outer membrane is a sieve permeable to
small molecules; intermembrane space is similar to cytoplasm in concentration
of small molecules
e) matrix - contains enzymes responsible
for many steps of metabolism, DNA, ribosomes, etc.
.
Plastids
Chloroplasts
are the most conspicuous plastids.
Each
bound by double membrane.
Contain
stroma - Enzyme-filled matrix.
Contain
grana made up of thylakoids.
Thylakoid
membranes contain chlorophyll.
Chromoplasts
and Leucoplasts are additional plastids found in many plants.
C. Chloroplasts (member of a class of
plant organelles called plastids) 1. Photosynthesis
a) light energy used to make ATP via
mechanism similar to that in miotochodnria
b) ATP is used to make CH2O from CO2 and
H2O
.
. Organelles Unique to
Plants - Plastids
Plastids are double membrane-bound organelles in plants.
They contain their own DNA (in nucleoid region) and ribosomes. They are
semi-autonomous and reproduce by fission similar to the division process in
prokaryotes. If plastids only arise from other plastids and cant be built
"from scratch", then where do they come from? The egg. Plastids are
inherited cytoplasmically, primarily through the female - however, there are
examples of paternal inheritance of plastids.
The plastid DNA carries several genes
including the large subunit of rubisco and those for resistance to some
herbicides. The chemistry of the membranes differs from the plasma membrane -
plastid membranes are comprised of glycosylglycerides rather than phospholipids
(the phosphate in the polar head group in glycosylglycerides is replaced with
galactose or a related sugar).
There are several types of plastids
including:
Proplastids - small, precursors to the
other plastid types, found in young cells, actively growing tissues;
Chloroplasts - sites of photosynthesis
(energy capture). They contain photosynthetic pigments including chlorophyll,
carotenes and xanthophylls. The chloroplast is packed with membranes, called
thylakoids. The thylakoids may be stacked into pancake- like piles called grana
(granum, singular). The "liquidy" material in the chloroplast is the
stroma. A chloroplast is from 5-20 m in diameter and there are usually
50-200 per cell.
The chloroplast genome has about
145 Kbase pairs, it is smaller than that of the mitochondria (200
kbases). About 1/3 of the total cell DNA is extranuclear (in the
chloroplasts and mitochondria);
Chromoplasts - non-photosynthetic,
colored plastids; give some fruits (tomatoes, carrots) and flowers their color;
Amyloplasts - colorless, starch-storing
plastids;
Leucoplast - another term for amyloplast;
Etioplast - plastid whose development
into a chloroplast has been arrested (stopped). These contain a dark
crystalline body, prolamellar body, which is essentially a cluster of
thylakoids in a somewhat tubular form.
Plastids can differentiate and convert from one form into another. For example,
think about the ripening processing in tomato. Initially, green tomatoes have
oodles of chloroplasts which then begin to accumulate lycopene (red) and become
chromoplasts. Usually you find only chromoplasts or chloroplasts in a cell, but
not both.
Chloroplast
.
2. Structure
a)
2 - 5 ΅ in diameter
b)
3 membranes - outer membrane, inner membrane, and thylakoid membrane
c)
stroma - within inner membrane; contains enzymes for metabolism, DNA,
ribosomes, etc.
d)
thylakoids - disc-like sacks which stack producing grana. Contain membrane
proteins which absorb light and make ATP.
Chloroplasts
What are some of the structural features
of chloroplasts?
Endosymbiotic Hypothesis
What led to the formulation of this
hypothesis?
. Others
Microbodies - a general term for any
single membrane bound organelle typically derived from the ER that contain
catalase and/or hydrogen peroxide producing enzymes. This includes the
peroxisomes and glyoxisomes;
Microsomes - a "biochemical"
term for the fraction that is obtained from high speed centrifugation of cell
homogenates. It includes membrane fragments and ribosomes.
G. Peroxisomes
Membrane sac containing enzymes for metabolizing waste
products from photosynthesis, fats and amino acids. Hydrogen peroxide is a
product of metabolism in peroxisomes. Catalase, which breaks down the
peroxide is also present and serves as a marker enzyme for these organelles.
H. Glyoxisomes
Membrane sac containing enzymes for fat metabolism.
Especially common in seeds. Also contain catalase.
E.
Vacuoles: large vesicles used to segregate some compounds from the rest of the
cell
1.
Food Vacuoles -- produced by phagocytosis (plasma membrane enveloping large
particles)
2.
Plant Central vacuoles ... a) storage of organic compounds (including proteins)
and inorganic ions
b)
serves the functions of lysosomes in plant cells
.
5. Vacuoles; commonly found in plant
cells and yeast taking the place of lysosomes
6. Plasma Membrane
receives protein and lipid synthesized in
ER and modified in Golgi communicates via transport vesicles
.
Vacuoles
In
mature cells, 90% of volume may be taken up by central vacuoles bounded by
vacuolar membranes (tonoplasts).
Filled
with cell sap which helps maintain pressure within the cell.
Also
frequently contains water-soluble pigments.
V. Organelles Unique to
Plants - Vacuoles
This is the large, central cavity containing fluid, called
cell sap, found in plant cells. he vacuole is surrounded by a membrane
(tonoplast). Back to the water balloon in the box model - imagine the vacuole
to be analogous to another water balloon inside our protoplast balloon. This
water balloon is a separate entity that can be physically removed from the
cell. The vacuole is penetrated by strands of cytoplasm - transvacuolar
strands.
The tonoplast and
plasma membrane have different properties such as thickness (tonoplast
thicker).
Virtually every plant
cell has a large, well-developed vacuole that makes up to 90% or more of the
cell volume. Wow! Meristematic and embryonic cells are exceptions. Young
tissues have many small vacuoles. As the cell grows the vacuoles expand and
eventually coalesce. These small vacuoles appear to be derived from the Golgi.
The central vacuole
contains water, ions, organic acids, sugars, enzymes, and a variety of
secondary metabolites. Among the hydrolytic enzymes are proteases (digest
protein), ribonucleases (digest RNA) and glycosidases (break links between
monosaccharides). These enzymes are typically not used for recycling
cellular components but rather leak out on cell senescence. There are
smaller lytic vacuoles, which contain digestive enzymes, that are used for this
purpose. Another type of vacuole, protein bodies, are vacuoles that store
proteins.
Other Structures
Cell wall
-primary wall
- primarily cellulose, as well as hemicellulose, pectins - elastic to allow
growth
-secondary
wall - highly lignified for strength
Plasmodesmata
-membrane
lined channels between cells, part of symplast
. Plasmodesmata
are narrow channels in the cell wall. There is continuity between the Cytoplasm
and Plasma Membranes of adjacent cells. Consequently, the Protoplasts of each
cell are in direct communion, and constitute the Symplast.
Molecules can
pass from one cell to another via Plasmodesmata (Symplast).
Molecules can
also move through the Apoplast but they must cross the Plasmalemma to
enter the Symplast.
The movement
of Molecules in the Apoplast is governed by the rules of Chemistry and Physics.
The Movement
of Molecules in the Symplast is also governed by the rules above plus the rules
of Biology.
. Cell Wall Composition
Polysaccharides
(Polymers made from Sugars) constitute most of the cell wall.
Cellulose
is a Polymer of Glucose
Hemicellulose has Glucose as one of its principal components.
Pectins are principally composed of acidic sugars like galacturonic acid.
Phenolic
Compounds like Lignin may be present.
.
Proteins constitute a small fraction of the wall.
Structural
Proteins are frequently present.
Elastin
is a protein which appears to function in Wall Loosening.
Extensin
adds Rigidity to the wall.
Enzymes
may be present.
. The Principal Functions of the Cell Wall are to regulate Cell
VOLUME, SHAPE &
STRUCTURAL PROPERTIES.
Ecological
Importance
Cell
Walls constitute the Major Component of Carbon Flow through Ecosystems
Dead
cell Walls help determine Soil Structure
. Functional
Overview
The Cell Wall
is a Cellular Exoskeleton (External) & thus provides Structural Support.
It is
Necessary for the development of Specialized Cell Shapes. Otherwise, all
cells would be spherical.
It is
Required for Water Relations (Turgor Pressure would not develop without a Cell
Wall).
Making
Fuel from Plant Biomass: One Plant Biologists View
You
all know that an important target of recent public and private initiatives is
to make the production of biofuels, ethanol and other energy-rich small
molecules, economically sustainable.
The conversion of lignocellulosic
biomass to biofuels requires the integration of many harvest,
postharvest, and physical, chemical and biochemical process engineering steps.
Lignocellulosic biomass
= plant cell walls!
Who must be involved
in research to make the utilization of plant biomass for energy production
feasible?
Microbiologists
- discovery of microbes for efficient conversion of diverse biomass-derived
small molecules into energy molecules and descriptions of ways to manage
these microbes optimally
Engineers
- systems for efficient field to pump harvest, production and delivery and
development of machines for optimal use of new fuels and energy sources
Enzymologists
- identification of enzymes to use to optimize the breakdown of biomass
polymers into useful small molecules for microbe use
There are many ways that
researchers in the Plant Sciences department can and should be involved:
Identification of wild
and cultivated plants that have qualities that suit them for
use as feedstocks for bioenergy production
Genetic
improvement of these plants to further enhance their
potential utility
Devising
crop management (pre- and postharvest) systems
Identifying potential problems with
sustainability (loss of soil organic content, use/overuse of fertilizers,
etc.)
Identifying
and testing of strategies for making plants more compatible with the
bioconversion process itself
The fundamental building block of the
plant body is the plant cell. The outer
boundary of the plant cell is the cell wall.
Cell walls are primary (1°)
1°
walls are extensible.
They have little (or no)
lignin, they may contain simple phenolic cross-links.
Cell walls are secondary
(2°)
2°
walls are not extensible (they are found in support tissues, water-conducting
cells).
They contain lignin.
They are produced by
cells to the inside of the 1°cell wall,
just outside of the cell membrane.
A
given plant has both 1° and 2°
walls.
The
plant cell wall
Is
an important source of strength (rigidity) for plant cells and, as such,
supports the shape of plant cells, tissues and organs.
It
is also an important barrier to pathogens and insects. They generally try to breach that barrier by
producing and secreting cell wall-degrading enzymes.
However,
because the barrier is made of sugars and amino acids, the wall itself is also food
for insects and pathogens.
Because
of its composition, the wall is also a potentially important feedstock for
production of biofuels
particularly if we can learn to operate like
insects and pathogens and take it apart efficiently.
An
engineering view of this wall might compare it to a reinforced concrete slab.
Cellulose
& hemicellulosic polysaccharides are
the rebar and wire
Pectins
are the concrete
Two
interacting networks fill the same space. But, this is a fabric and it
has porosity.
A flow diagram for field-to-fuel
utilization of the ligno-cellulose in crop residues or dedicated biomass energy
crops would look something like this:
Plant cultivation &
management
Harvest & postharvest
management
Pretreatment
Cellulose digestion
Fermentation
One
important goal of pretreatment is to make the cellulose of biomass more
accessible to cellulases. Pretreatment
should:
open
up the organization of the cell wall so that enzymes can reach cellulose
and
open
up the cellulose microfibril so that cellulases can digest the individual
glucose polymers more rapidly and completely.
Our
impression is that lessening the costs (energy, environmental
protection/clean-up, physical plant) for biomass pretreatments is an
important goal. Another goal would be to
use, rather than lose, the sugars in non-cellulosic polymers.
What
shape would plant participation in the conversion process have?
How
would we go about convincing the plant to help us out?
We
feel that the keys to answering these questions can be found in an understanding
of the ways plant cells make, assemble and disassemble their cell walls.
The
cell wall of a grain or biomass crop could be genetically manipulated
so that a more biomass conversion compliant wall is made. That is, we could genetically engineer
changes in the walls make-up.
In
this age of molecular biology, researchers have identified many of the genes
that encode cell wall proteins and enzymes that are important in the
synthesis of cell wall polysaccharides and lignin.
Lignin
is a particularly good target for this approach. Lignin makes forage crops less digestible and
makes the production of pulp for paper manufacture more expensive. It gets in the way!
However,
the plant has to function as a plant before its cell walls are to be
available for production of biofuels and cell walls play important roles in
plant development.
Modifying
a plants production of its wall to improve bioconversion is likely to be the
goal for a long-term project.
The other approach to manipulating cell
wall participation in bioconversion is to enhance the plants natural talent
for disassembly of its own cell walls.
All
plants actively modify their cell walls, at specific
times, as they grow and develop.
Can we enhance and manage this
innate capacity for wall breakdown so as
to make biomass and crop plants that assist in their own bioconversion?
Pathogens
break down cell walls of their plant hosts, if plant cells are
to grow they must selectively digest their own cell walls, when fruits
ripen they digest their cell walls so that the fruits soften, etc.
The messages from these observations are
that:
In
nature there is a great diversity of cell wall digesting enzymes
Plants
and microbes can synthesize cell wall-digesting enzymes and export them into
the cell wall space
With
either tomato fruit fate, wall disassembly is accomplished with the
secretion of wall-digesting enzymes into the cell wall space.
Those very skilled individuals who worked
to drop the Seattle Super Dome directly into the space where it had been
sitting for several years studied its structure intensively before they decided
where to place their explosive charges.
We know a great deal
about the structure that we want to deconstruct.
Can we identify the
correct enzymatic charges needed to deconstruct cell walls?
Can
we manage the timing of our internal explosion?
We
have proposed to Chevron to enhance the value of wheat as a biofuel feedstock
by engineering the start of xylan disassembly after the grain has ripened
and been harvested.
The
idea is that this self-digestion will reduce (perhaps eliminate) the
need for expensive pretreatments, thus making wheat cell wall bioconversion
and production of biofuel more economical.
Cells and
Tissues
-Cell types
-parenchyma -
generalized thin-walled cell with many forms and functions
-collenchyma - unevenly thickened wall
-sclerenchyma - highly thickened and lignified wall
Vascular
system - the plumbing system
-Located in
central cylinder (stele) of root, and in vascular bundles in stems and leaves
Meristematic
Cells
Meristematic
cells give rise to all three fundamental mature cell types. Their major
function is cell division, and so their cell cycle indeed cycles. The
walls are thin, the vacuole is largely missing, the plastids are immature, etc.
The stages of mitosis and cytokinesis are reviewed.
Parenchyma
Cells
These cells
are the biochemistry machines of the plant. They are alive at maturity and are
specialized in any number of structural and biochemical ways. Other than
support functions, this cell type is the basis for all plant structure
and function.
Parenchyma
cells have thin primary walls, and highly functional cytoplasm. The cells are
alive at maturity and are responsible for a wide range of biochemical function.
For example, other than xylem in vascular bundles, the leaf is composed of
parenchyma cells. Some, as in the epidermis, are specialized for light
penetration, regulating gas exchange, or anti-herbivory physiology. Other
cells, as in the mesophyll, are specialized for photosynthesis or phloem
loading.
Parenchyma
Tissues are usually massive and contain many adjacent Parenchyma cells. This
image is from a stem, stained with Toluidine Blue.
Parenchyma cells can be
elongated, Parenchyma cells can be branched.
Collenchyma
Cells
Collenchyma
cells are also alive at maturity and have only a primary wall. These cells
mature from meristem derivatives. They pass briefly through a stage resembling
parenchyma, however they are determined to differentiate into collenchyma, and
this fact is quite obvious from the very earliest stages. Plastids do not
develop and secretory apparatus (ER and Golgi) proliferates to assist in the
accumulation of additional primary wall. This is laid down where three or more
cells come in contact. Areas of wall where only two cells come in contact
remain as thin as those of parenchyma cells.
Collenchyma
cells bear a strong resemblance to Parenchyma. However, they have some
distinguishing traits. They occur in groups just beneath the Epidermis. They
have a primary cell wall which contains lots of pectins. Thus, they stain pink
with Toluidine Blue. The cell wall is unevenly thickened, however.
The
thickenings can occur at the corners of adjacent cells. This is called Angular
Collenchyma. This is illustrated in this embossed image.
Sclerenchyma
Cells
These cells
are hard and brittle (as you might expect from the root: scler-. The cells
develop an extensive secondary cell wall (laid down on the inside of the
primary wall). This wall is invested with lignin, making it extremely hard.
Lignin, plus suberin and/or cutin make the wall waterproof as well. Thus, these
cells cannot survive for long as they cannot exchange materials well enough for
active (or even maintaining) metabolism. They are typically dead at functional
maturity...the cytoplasm is missing by the time the cell can begin to carry out
its function.
Functions for
sclerenchyma cells include discouraging herbivory (hard cells that rip open
digestive passages in small insect larval stages, hard cells forming a pit wall
in a peach fruit), support (the wood in a tree trunk, fibers in large herbs),
and conduction (hollow cells lined end-to-end in xylem with cytoplasm and end
walls missing).
Sclerenchyma
includes the fibers used for making thread and fabric...particularly the fibers
from flax that are spun and woven into linen..
Sclereid under
construction. Note the similarity in shape to the Parenchyma cell above.
However, note the difference in wall thickness. The new wall is called
Secondary and is deposited after the cell has ceased enlargement.
Parenchyma cells can
eventually develop into Sclerenchyma cells. However, this is not usually the
case. The distinguishing features of Sclerenchyma are the presence of a thick
Secondary Wall which has highly organized cellulose microfibrils, and usually
contains Lignin. Viewed with Phase optics.
The design
and function is to build and maintain the special unevenly thick primary cell
wall. The cells are also typically quite elongate. The role of this cell type
is to support the plant in areas still growing in length. The primary wall
lacks lignin that would make it brittle, so this cell type provides what could
be called plastic support. Support that can hold a young stem or petiole into
the air, but in cells that can be stretched as the cells around them elongate.
Stretchable support (without elastic snap-back) is a good way to describe what
collenchyma does. Parts of the strings in celery are collenchyma.
Meristematic Tissues
Meristems
- Permanent regions of active cell division.
Apical
Meristems - Found at the tips of roots and shoots.
Increase
in length as the apical meristems produce new cells (primary growth).
Primary
Meristems
» Protoderm
» Ground
Meristem
» Procambium
Meristematic Tissues
Lateral
Meristems - Produce tissues that increase the girth of roots and stems.
Secondary
Growth
Vascular
Cambium - Produces secondary tissues that function primarily in support and
conduction.
» Thin
cylindrical cells.
Cork
Cambium - Lies outside vascular cambium just inside the outer bark.
Meristematic Tissues
Grasses
and related plants do not have vascular cambium or cork cambium, but do have
apical meristems in the vicinity of the nodes.
Intercalary
meristems
Develop
at intervals along stems where they add to stem length.
Tissues Produced By Meristems
Simple
Tissues
Parenchyma
- Composed of parenchyma cells. Tend to have large vacuoles and many contain
various secretions.
Aerenchyma
- Parenchyma tissue with extensive connected air spaces.
Chlorenchyma
- Parenchyma cells containing chloroplasts.
Simple Tissues
Collenchyma
- Contain living cytoplasm and may live an extended time.
Provide
flexible support for organs.
Sclerenchyma
- Cells with thick, tough, secondary walls, normally impregnated with lignin.
Sclerids
- Stone Cells
Fibers
- Contain Lumen
Complex Tissues
Complex
tissues are made up of two or more cell types.
Xylem
- Chief conducting tissue for water and minerals absorbed by the roots.
Vessels
- Made of vessel elements.
Long
tubes open at each end.
Tracheids
- Tapered at the ends with pits that allow water passage between cells.
Rays
- Lateral conduction.
Complex Tissues
Phloem
- Conducts dissolved food materials produced by photosynthesis throughout the
plant.
Sieve
Tube Members - Large, cylindrical
Sieve
Plates - Porous region
Companion
Cells - Narrow, tapered
Complex Tissues
Epidermis - Outermost layer of cells.
One
cell thick
Most
secrete fatty substance, cutin, on the surface of the outer walls.
» Forms
cuticle.
Root
epidermal cells produce root hairs.
Leaves
have stomata bordered by pairs of guard cells.
Complex Tissues
Periderm
- Constitutes outer bark.
Primarily
composed of cork cells.
Cytoplasm
of corks cells secretes suberin into the walls.
Some
parts of cork cambium form loosely arranged pockets of parenchyma cells that
protrude through the surface of the periderm.
Lenticels
Complex Tissues
Secretory
Cells and Tissue
Secretory
cells may function individually or as part of a secretory tissue.
Flower
nectar
Citrus
oils
Glandular
hair mucilage
Latex
-Xylem
-consists of
hollow tracheids and vessel members
-dead at
functional maturity; highly lignified cells involved in water transport and
structure
-Phloem-
-consists of
sieve tube cells and companions
-alive at
functional maturity, but has no nucleus; involved in dissolved solute transport
Organs
-Roots,
leaves, stems
-variety is
key
Xylem
is clearly visible in the attached illustration. It is harder to specifically identify the
Phloem.
Plant Cell Types
This lecture on plant cell
types derives primarily from a series of slides presented in lecture to support
the lecture handout:
