Dr Rita Mahapatra Assistant Professor Neotech College of applied Science and Research Virod Vadodara Plant cell structure The term c ell Is derived from the Latin cella meaning storeroom ID: 935088
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Slide1
Biochemistry Sem-VPaper-C-2, Unit-1
Dr. Rita Mahapatra
Assistant Professor
Neotech
College of applied Science and Research,
Virod
, Vadodara
Slide2Plant cell structure
The term
c
ell
Is derived
from
the Latin
cella
, meaning storeroom
or
chamber
was given by Robert Hooke in 1665.
Plants are
multicellular
organisms composed of millions of cells with specialized functions. At maturity, such specialized cells may differ greatly from one another in their structures.
However, all plant cells have the same basic eukaryotic organization (Fig 1): They contain
1: Cytoplasm (Chloroplast, mitochondria etc.)
2:
Nucleus
3: Cell membrane
4: Cell wall
5: Chromosomes
6: Plasmodesmata
7: Filamentous cytoskeleton
Slide3Fig 1. Plant cell structure
Slide4Cell membraneThe cytoplasm and the nucleus and other parts of the cell are enclosed within the cell
membrane or plasma membrane
which separates cell from one another and also the cell from the surrounding medium.
The membrane is porous and allows the movement of substances or materials both inward and outward. The yellow outline in this diagram is the cell membrane.
Slide5Cell Wall
The cell wall is the
most characteristic feature of a plant cell
The
cell wall is always
non-living but is formed and maintained
by
the
living organism
Its
primary function is
to provide protection to the contents of cell
Due
to
semi-rigid nature, the cell walls are responsible for giving
shapes to different kinds of cells during cell differentiation of
Tissues
In
multicellular
and woody plants of cell wall is differentiated into
three parts
i.e.,
the middle lamella, the primary wall and
secondary wall .
The cell wall is a very tough, flexible and sometimes fairly rigid layer that surrounds plant cells. It surrounds the cell membrane and provides these cells with structural support and protection.
In addition the cell wall is acting as a filtering mechanism. A major function of the cell wall is to act as a pressure vessel, preventing over-expansion when water enters the cell. The green outline in this diagram is the cell wall:-
Slide6The middle lamella
It is a
common structure between
adjacent cells and therefore,
binds them
with each other.
It is an
amorphous layer and is
composed of
calcium and magnesium
pectate
.The middle lamella remains unlignifiedin case of softer living tissues namelyParenchyma, collenchyma and arenchyma, but in woody tissues Sclerenchyma it becomes highly lignified
Slide7The primary cell wallConsists of cellulose (
45%),
hemicellulose
(25%),
pectins
(
35%) and structural proteins (
upto
8%) on the basis of dry
weight
The
primary wall is thin and elasticIt is capable of growth and expansionThe backbone of the primary wall is formed by the cellulosefibrils.The matrix is composed of hemicellulose, pectin, gums,tannins, resins, silica, waxes etc. and small structured proteins
Slide8Secondary cell wall
The
20 wall is
very thick (lignin), rigid and inelastic and consists of three
layers known as
S1 (outer), S2 (middle) and S3 (inner)
The
microfibrils
in these layers run parallel to each other but the
directions are different in three layers.
The
microfibrils are transversely arranged in the S3 and are at an angle of10 -200 to the longitudinal axis in S2 and are at the angle of 500 in S1The lignin is formed from three different phenyl propanoid alcohols: coniferyl,
coumaryl
and
sinapyl
alcohols.
Lignin is covalently bonded to cellulose and other polysaccharides of cell wall.
Slide9Difference between the primary andsecondary cell wall
Slide10Functions of cell wallThey determine the morphology, growth, and development of plant
cells.
They
protect the protoplasm from invasion by viral, bacterial and
fungal pathogens.
They are rigid structures and thus help the plant
in withstanding the
gravitational forces.
They are involved in the
transport of materials and metabolites
into and out of cell.
They withstand the turgor pressure which develops within the cells due to high osmotic pressure.
Slide11Nucleus
The nucleus is
double
membrane-enclosed organelle found in eukaryotic cells. The nucleus is generally spherical and located in the centre of the cell. The nucleus contains thread like structures called chromosomes which carry genes. Gene is a unit of inheritance in living organisms.
The function of the nucleus is to maintain the integrity of these genes and to control the activities of the cell by regulating gene expression—the nucleus is, therefore, the control center of the cell
.
Nuclei contain a densely granular region, called
the
nucleolus
(plural
nucleoli), that is the site of ribosome
synthesis. A specific amino acid sequence called the nuclear localization signal is required for a protein to
gain
entry
into the nucleus.
The main structures making up the nucleus are the nuclear envelope, a double membrane that encloses the entire organelle and isolates its contents from the cellular cytoplasm, the nucleolus and nuclear pores.
Nuclear pores regulate the transport of molecules across the envelope.
The nucleolus is a smaller spherical body in the nucleus.
Slide12The jelly- like substance present between the cell membrane and nucleus is known as the cytoplasm. The cytoplasm is about 80% water and usually colorless . Various other components, or organelles, of cells are present in the cytoplasm. These are :Mitochondria
Chloroplast
Golgi bodies
Ribosomes
Endoplasmic reticulum
Lysosomes
Vacuole
Peroxisomes
etc.
Cytoplasm
Slide13Chloroplast
Chloroplast belong to another group of double membrane–enclosed organelles called
plastids.
Chloroplast membranes are rich in glycosylglycerides.
Chloroplast membranes contain chlorophyll
and it’s associated proteins and are the sites of photosynthesis.
In addition to their inner and outer envelope membranes, chloroplasts possess a third system of membranes called
thylakoids
. A stack of
hylakoids
forms a
granum (plural grana) (Fig. 2). Proteins and pigments (chlorophylls and carotenoids
) that function in the photochemical events of photosynthesis are embedded in the
thylakoid
membrane.
The fluid compartment surrounding the
thylakoids
, called the
stroma, is analogous to the matrix of the
mitochondrion.
Adjacent
grana
are connected by
unstacked
membranes called
stroma lamellae
(singular
lamella).
Plastids that contain high concentrations of carotenoid pigments rather than chlorophyll are called
chromoplasts
.
They are one of the causes of the yellow, orange, or red colors of many fruits and flowers, as well as of autumn leaves
Slide14Fig. 2. Chloroplast
Slide15Cont.
Non pigmented
plastids are called
leucoplasts. The most
important type of leucoplast is the
amyloplast
, a
starchstoring
plastid.
Amyloplasts
are abundant in storage tissues of the shoot and root, and in seeds. Specialized amyloplasts in the root cap also serve as gravity sensors that direct root growth downward into the soil.Chlorophylls are pigments in chloroplast absorb red and blue light and reflect green and yellow light to excite electron (e-) – plant appears green.Plant absorbs CO2, H2O and O2 as raw material of photosynthesis.Carbon dioxide + water → Sugar + Oxygen +
Water + Sunlight
6 CO2 + 6H2O
→
C6H12O6 + 6O2
Slide16Mitochondria
Mitochondria (singular
mitochondrion) are the cellular sites of respiration, a process
in which the energy released from sugar metabolism is used for the synthesis of ATP (adenosine
triphosphate
) from ADP (adenosine
diphosphate
) and inorganic phosphate (Pi) .
Mitochondria can vary in shape from spherical to tubular, but they all have a
mooth
outer membrane and a highly convoluted inner membrane (Fig. 3).
The infoldings of the inner membrane are called cristae (singular crista).The compartment enclosed by the inner membrane, the mitochondrial matrix, contains the enzymes of the pathway of intermediary metabolism called the Krebs cycle.
In contrast to the mitochondrial outer membrane and all other membranes in the cell, the inner membrane of a mitochondrion is almost 70% protein and contains some phospholipids that are unique to the organelle (e.g.,
cardiolipin
).
The proteins in and on the inner membrane have special enzymatic and transport capacities
.
The
transmembrane
enzyme
ATP synthase is coupled to the
phosphorylation
of
ADP to produce ATP.
Slide17Fig.3 Mitochondria
Slide18Mitochondria and Chloroplasts AreSemiautonomous Organelles
Both mitochondria and chloroplasts contain their own DNA and protein-synthesizing machinery (70S
ribosomes
, transfer RNAs, and other components) and are believed to have evolved from
endosymbiotic
bacteria.
Both plastids and mitochondria divide by fission, and mitochondria can also undergo extensive fusion to form elongated structures or networks.
The DNA of Mitochondria 200 Kb and chloroplast 145Kb, these organelles is in the form of circular chromosomes, similar to those of bacteria and very different from the linear chromosomes in the nucleus.
These DNA circles are localized in specific regions of the mitochondrial matrix or plastid stroma called
nucleoids
.
DNA replication in both mitochondria and chloroplasts is independent of DNA replication in the nucleus.
Slide19PeroxisomesPeroxisomes are found in all eukaryotic organisms, and
in plants they are present in photosynthetic cells
Peroxisomes
function both in the removal of
hydrogens
from organic substrates, consuming O2 in the process, according to the following reaction:
RH2 + O2 → R + H2O2
(where
R is the organic
substrate)
The
potentially harmful peroxide produced in these reactions is broken down in peroxisomes by the enzyme catalase, according to the following reaction:H2O2 → H2O + 1⁄2O2Although some oxygen is regenerated during the catalasereaction, there is a net consumption of oxygen overall.
Slide20GlyoxysomeAnother type of microbody
, the
glyoxysome
, is present
in oil-storing seeds.
Glyoxysomes
contain the
glyoxylate
cycle enzymes, which help convert stored fatty acids into
sugars that can be translocated throughout the young plant to provide energy for growth
Because both types of
microbodies (peroxisome & glyoxysome) carry out oxidative reactions, it has been suggested they may have evolved from primitive respiratory organelles that were superseded by mitochondria.
Slide21Vacuoles
Mature living plant cells contain large, water-filled
central vacuoles
that can occupy 80 to 90% of the total volume
of the cell.
Each
vacuole is surrounded by
a
vacuolar
membrane, or
tonoplast
. Many cells also have cytoplasmic strands that run through the vacuole, but each transvacuolar strand is surrounded by the tonoplast.The vacuole contains water and dissolved inorganic ions, organic
acids,
ugars
, enzymes, and a variety of
secondary metabolites,
which often play roles in plant defense.
Active
solute accumulation provides the
osmotic driving
force for water uptake by the vacuole, which
is required
for plant cell enlargement.
The
turgor
pressure generated
by this water uptake provides the
structural rigidity
needed to keep herbaceous plants upright,
since they
lack the lignified support tissues of woody plants
.
Slide22Vacuoles contain many hydrolytic enzymes, such as proteases, ribonucleases, glycosidases
, and
phosphatases
, as well as
peroxidases
and a variety of secondary metabolites, which often play roles in plant defense. Active solute accumulation provides the osmotic driving force for water uptake by the vacuole, which is required for plant cell
nlargement
.
The
turgor
pressure generated by this water uptake provides the structural rigidity needed to keep herbaceous plants upright, since they lack the lignified support tissues of woody plants.Specialized protein-storing vacuoles, called protein bodies, are abundant in seeds. During germination the
storage proteins
in the protein bodies are hydrolyzed to
amino acids
and exported to the cytosol for use in protein synthesis.
The hydrolytic enzymes are stored in
specialized lytic
vacuoles, which fuse with the protein bodies to
initiate
the
breakdown process
Slide23Plasmodesmata
Plasmodesmata are microscopic channels which allow molecules to travel between plant cells. Unlike animal cells, every plant cell is surrounded by a cell wall. Neighboring plant cells are therefore separated by a pair of cell walls, forming an extracellular domain known as the apoplast.
Although cell walls allow small soluble proteins and other solutes to pass through them, Plasmodesmata enable direct, regulated,
symplastic
intercellular transport of substances between cells
.
Plasmodesmata (singular
plasmodesma
) are tubular extensions
of the plasma membrane, 40 to 50 nm in diameter, that traverse the cell wall and connect the
cytoplasms
of adjacent cells. Because most plant cells are interconnected in this way, their
cytoplasms
form a continuum referred to as the
symplast
. Intercellular transport of solutes through
plasmodesmata
is thus called
symplastic
transport
Slide24Filamentous cytoskeleton
The
cytoskeletal
components—microtubules,
microfilaments, and intermediate filaments—participate
in a
variety of
processes involving intracellular movements,
such as
mitosis,
cytoplasmic
streaming, secretory vesicle transport cell plate formation, and cellulose microfibril deposition.The process by which cells reproduce is called the cell cycle.The filamentous cytoskeleton is a network of fibers composed of proteins contained within a cell's cytoplasm. It is a dynamic structure, parts of which are constantly destroyed, renewed or newly constructed.
Here is a multitude of functions the cytoskeleton can perform: It gives the cell shape and mechanical resistance to deformation, it stabilizes entire tissues, it can actively contract, hereby deforming the cell and the cell's environment and allowing cells to migrate, it divides chromosomes.
It
is involved in the division of a mother cell into two daughter cells etc. The functions which this cytoskeleton can perform depend on the type of cell and the organism.
Slide25Functions of Water in Plants
Water is important in the life of plants because it makes
up the
matrix and medium in which most
biochemical processes
essential for life take
place.
It
has been said that the study of plant physiology is, for the most part, the study of plant water relations. This is understandable, given the central role water plays in a large number of plant processes.
Among the many functions of water in plants are the following: · it serves as a medium (and sometimes substrate) for biochemical reactions in cells, since many enzymes are dissolved in the cell water · structural support – water provides the “
turgor
pressure” that gives many cells their shape; thus, many tissues will lose their structure and wilt when water availability is inadequate.cell enlargement – turgor pressure provides the physical force needed to expand cells during growth. Transport of solutes between organs, via the xylem and phloem vessels evaporative cooling of leaves during transpiration.Next to light, water availability is probably the single most important environmental factor affecting plant growth. Accordingly, plants have evolved with complex physiological strategies for regulating water use, including, but not limited to, minutes timescale regulation of
stomatal
apertures in response to sudden changes in environmental conditions. In cropping situations
Worldwide, water deficits constitute the single largest cause of crop failure.
Slide26Diffusion
The net, random movement of individual
molecules from one area to another. The
molecules move from [hi] → [low], following
a concentration gradient.
Another way of stating this is that the molecules move
from an area of high free energy (higher concentration)
to one of low free energy (lower concentration).
The net movement stops when a
dynamic equilibrium is
achieved.
Slide27Some studies indicated that diffusion directly across the lipid bilayer was not sufficient to account for
observed rates
of water movement across membranes, but the
evidence in
support of microscopic pores was not compelling.
This uncertainty was put to rest with the recent
discovery of
aquaporins
.
Aquaporins
are integral membrane proteins that form water-selective channels across the membrane. Because water diffuses faster through such channels than through a lipid bilayer, aquaporins facilitate water movement into plant cells
.
Water can cross plant membranes by diffusion of individual water molecules through the
embrane
bilayer
, as shown on the left, and by microscopic bulk
flow of
water molecules through a
water- elective
pore formed by integral membrane proteins such as
aquaporins
as shown in the diagram
Slide28Slide29Osmosis
Water potential is a measure of the energy state of water.
Determines the direction and movement of water.
Unit for water potential
MegaPascal
Mpa
Ψ pure water at 1
atm
= 0
Mpa
Ψ=Ψs + ΨpΨ= water potentialΨs=solute potential (osmotic potential) –Always negativeΨp=(pressure potential)Water molecules move from higher water potential to lower water potential
The spontaneous net movement of solvent molecules through a partially permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides –dynamic equilibrium.
Slide30ABSORPTION OF WATER
Water
in the soil is mostly and abundantly, under
normal conditions
, is available in the form of Capillary water
. W
ater plays a crucial role
in the life of the plant. For
every gram
of organic matter made by the plant, approximately 500 g of
water is
absorbed by the roots, transported through the plant body and lost to the atmosphere.In the soil the space in between soil particle forms a network of spaces, which normally is filled with water. The
water that is present
in such
spaces is called capillary water
.
Land plants absorbs water by
(1) An
extensive root
system to
extract water from the soil;
(
2) A
low-resistance
pathway through
the xylem vessel elements and
tracheids
to
bring water
to the leaves;
(
3) A
hydrophobic cuticle covering
the surfaces
of the plant to reduce evaporation
;
(
4) M
icroscopic stomata
on the leaf surface to allow gas exchange; and
(5) Guard
cells to regulate the diameter (and
diffusional
resistance) of
the
stomatal
aperture
.
Slide31In plants, following two pathways are involved in the water movement. They are(1) Apoplastic
pathway
(2)
Symplastic
pathway
(3)
Transmembrane
pathway
1
.
Apoplastic
pathway : The apoplastic movement of water in plants occurs exclusively through the cell wall without crossing any membranes. The cortex receive majority of water through apoplastic way as loosely bound cortical cells do not offer any
resistance. But the movement of water in root beyond cortex
apoplastic
pathway is blocked by
casparian
strip present in the endodermis.
Slide322. Symplastic pathway
The movement of water from one cell to other cell through the
plasmodesmata
is called the
symplastic
pathway
of water movement. This pathway comprises the network of cytoplasm of all cells inter-connected
by
plasmodermata
.
Slide333. The transmembrane pathway is the route
followed by
water that sequentially enters a cell on one
side, exits
the cell on the other side, enters the next in
the series
, and so on. In this pathway, water crosses
at least
two membranes for each cell in its path (
the plasma
membrane on entering and on exiting).
Transport across the tonoplast may also be involved.
Slide34Translocation and conduction of water and minerals
Some aspects of phloem translocation
have
been
well established
by extensive research over many years.
These include
the following:
The
pathway of
translocation- Sugars
and other organic materials are conducted throughout the plant in the phloem, specifically in cells called sieve elements. Sieve elements display a variety of structural adaptations that make them well suited for transport.Patterns of translocation. Materials are translocated
in
the
phloem from sources (areas of
photosynthate
supply
) to sinks (areas of metabolism or storage of
photosynthate
). Sources are usually mature
leaves. Sinks
include organs such as roots and
immature leaves
and fruits.
Materials
translocated in the phloem. The
translocated
solutes
are mainly carbohydrates, and sucrose is
the most
commonly translocated sugar.
Phloem
sap
also contains
other organic molecules, such as
amino acids
, proteins, and plant hormones, as well as
inorganic ions.
Slide35Rates of movement. Rates of movement in the phloem are quite rapid, well in excess of rates of diffusion. Velocities average 1 m h–1, and mass transfer ratesrange
from 1 to 15 g h–1 cm–2 of sieve elements.
Other aspects of phloem translocation require
further investigation
, and most of these are being studied
intensively at
the present time. These aspects include the following:
Phloem
loading and unloading. Transport of sugars
into
and
out of the sieve elements is called sieve element loading and unloading, respectively.Mechanism of translocation.Photosynthate allocation and partitioning.
Slide36Guttation
Guttation
is the appearance of drops
of xylem sap on the tips or edges of leaves of some vascular plants, such as grasses.
Guttation
is not to be confused with dew, which condenses from the atmosphere onto the plant surface Secretion of water on to the surface of leaves through specialized pores, or
hydathodes
.
The main cause of
guttation
in plants is root pressure, during night when root pressure is high sometimes den due to this pressure watery drops ooze out with the assistance of special structures which help in
guttation called the hydathodes.
Slide37Slide38TranspirationDuring the plant’s lifetime, water equivalent to 100 times the fresh weight of the plant may be lost through the leaf surfaces. Such water loss is called
transpiration.
Transpiration is an important means of dissipating the heat input from sunlight. Heat dissipates because the water molecules that escape into the atmosphere have higher than- average energy, which breaks the bonds holding them in the liquid.
For
a typical leaf, nearly half of the net heat input from sunlight is dissipated by transpiration
.
Latent heat of vaporization is
the energy needed to separate molecules from the liquid phase and move them into the gas phase at constant temperature—a process that occurs during transpiration.
For water at 25°C, the heat of vaporization is 44 kJ mol–1—the highest value known for any liquid. Most of this energy is used to break hydrogen bonds between water molecules.
Slide391. Stomatal transpiration: Transpiration
that occurs
through stomata
called
stomatal
transpiration
. This type
of transpiration
only occurs in
its presence
of sunlight (in daytime).
Because stomata open in the present of sunlight and close in the darkness. In this method plants give out 80-90% water in the form of vapor.
Slide402. Cuticular transpiration:
Transpiration that
occurs through
the cuticle or cracks
of thin
cuticle layer of leaves
and stems
is said to be
cuticular
transpiration
.
This is a day-night process. In this process, 5-10% water is given out in the form of vapor.
Slide413. Lenticular transpiration:
Sometimes transpiration
occurs through
lenticels, the
small opening
in the corky
tissue covering
stems and twigs,
and this
type of transpiration is
said to
be the lenticular transpiration. In this process, only 0.1% water is given off of the forms of vapor.
Slide42Transpiration is a process similar to evaporation.It is a part of the water cycle, and it is the loss of water vapor from parts of plants (similar to sweating), especially in leaves but also in stems, flowers and roots.
Leaf surfaces are dotted with openings which are collectively called stomata, and in most plants they are more numerous on the undersides of the foliage.
The stomata are bordered by guard cells that open and close the pore.
Leaf transpiration occurs through stomata
.
An Increase in Guard Cell
Turgor
Pressure Opens the Stomata
Guard cells function as multisensory hydraulic valves.
environmental
factors such as light intensity and quality,
temperature, relative humidity, and intracellular CO2 concentrations are sensed by guard cells, and these signals are integrated into well-defined stomatal responses. If leaves kept in the
dark are illuminated, the light stimulus is perceived
by the
guard cells as an opening signal, triggering a series
of responses
that result in opening of the
stomatal pore.
Slide43In guard cells the microfibril organization is different.Kidney-shaped guard cells have cellulose
microfibrils
fanning out
radially
from the pore (
Fig. A
). Thus the
cell girth
is reinforced like a steel-belted radial tire, and
the guard cells curve outward during
stomatal opening In grasses, the dumbbell-shaped guard cells function like beams with inflatable ends.As the bulbous ends of the cells increase in volume and swell, the beams are separated from each other and the slit between them widens (
Fig. B).
Guard cell
Slide44Mechanism of Transpiration
The
Cohesion–Tension Theory
Explains
Water. Transport
in the
Xylem. In
theory, the pressure gradients needed to move
water through
the xylem could result from the generation of
positive pressures
at the base of the plant or negative pressures at the top of the plant.It is mentioned previously that some roots can develop positive hydrostatic pressure in their xylem—the so-called root pressure.However, root
pressure is
typically less than 0.1
MPa
and disappears when
the transpiration
rate is high, so it is clearly inadequate to move water up a tall tree.
Instead, the water at the top of a tree develops a
large tension
(a negative hydrostatic pressure), and this
tension
pulls
water through the xylem. This mechanism, first
proposed
toward
the end of the nineteenth century, is
called the
cohesion–tension theory of sap ascent because
it
requires
the cohesive properties of water to sustain
large tensions
in the xylem water
columns.
Slide45Root pressure theoryRoot pressure is most likely to occur when soil
water potentials
are high and transpiration rates are low.
When transpiration
rates are high, water is taken up so
rapidly into
the leaves and lost to the atmosphere that a
positive pressure
never develops in the xylem.
Plants that develop root pressure frequently produce
liquid droplets
on the edges of their leaves, a phenomenon known as guttation.
Slide46Water in the plant can be considered a continuous hydraulic system, connecting the water in the soil with the water
vapor in the atmosphere.
Transpiration
is
regulated principally
by the guard cells, which regulate the
stomatal
pore
size to meet the photosynthetic demand for
CO2 uptake
while minimizing water loss to the atmosphere.
Water evaporation from the cell walls of the leaf mesophyll cells generates large negative pressures (or tensions) in the apoplastic water. These negative pressures are transmitted to the xylem, and they pull water through the long xylem conduition.
Although aspects of the cohesion–tension theory of sap ascent are intermittently debated, an overwhelming body of evidence supports the idea that water transport in the xylem is driven by pressure gradients.
When transpiration is high, negative pressures in the xylem water may cause cavitation (embolisms) in the xylem.
Such embolisms can block water transport and lead to severe water deficits in the leaf.
Water deficits are commonplace in plants, necessitating a host of adaptive responses that modify the physiology and development of plants.
Water balance and Stress
Slide47Water deficit can be defined as any water content of a tissue or cell that is below the highest water content
exhibited at
the most hydrated state.
When
water deficit
develops slowly
enough to allow changes in
developmental processes
, water stress has several effects on growth,
one of
which is a limitation in leaf expansion. Leaf area
is important because photosynthesis is usually proportional to it. However, rapid leaf expansion can adversely affect water availability.Adaptation and acclimation to environmental stresses result from integrated events occurring at all levels of organization, from
the anatomical and morphological level
to the
cellular
, biochemical
, and molecular level. For
example, the wilting of leaves in response to water deficit reduces both
water loss from the leaf and exposure to incident
light, thereby
reducing heat stress on leaves
.
At the biochemical level, plants alter metabolism
in various
ways to accommodate environmental
stresses, including
producing
osmoregulatory
compounds such
as proline
and
glycine
betaine
to adapt
and acclimate to water
deficit, salinity
, chilling and freezing, heat, and oxygen
deficiency in
the root
biosphere.
Slide48ReferencesPlant Physiology, 3rd
ed
,
Lincoln
Taiz
and Eduardo
Zeiger
, Publisher
:
Sinauer
Associates; 3 edition (2002).Fundamental of biochemistry by D Voet, J.GVoet and C.W Pratt, John Wiley & Sons, Inc., New York, 2nd edition, 2005 Principles of Biochemistry by Albert Lehninger, W.H. Freeman & Company; 3rd edition (February 2000), ISBN-10: 1572591536
Botany by A. K Nanda