Pre-Midterm Flashcards
What is phyisology
branch of biology relating to the function of organs and organ systems, and how they work within the biological body to respond to challenges
Plant Physiology
The study of how different parts of plants function for many aspects of plant life.
Translocation in the Phloem
Source to sink
Chloroplast
powerhouse for plant life
C4 Photosynthesis
A CO2 pump, fast photosynthesis of C4 plants under high light intensity and high temperature
Phytohormones
regulation of many aspects in all stages of the plant life cycle
Water balance
important properties of water molecules
How to pull water through the xylem
Water potential
Movement of water in plants
water moves from soil to root
water gets through the root
water moves up through the xylem
water moves from leaf to air
History- the study of plant water relations
Malpighi and Grew (1670-1680s)
Observations of plant conducting tissues
They found out plant structures which are similar to animal vasculature
Important properties of water
water is cohesive
water is an excellent solvent
water can dissociate into ions
water has a high latent heat of vaporization
Water has a high tensile strength
Water is cohesive
No net charge to a water molecule, however electronegative
Electronegative
Attract the electrons of the covalent bond
Hydrogen bonding and polar structures
Good solvents for ionic substances, sugar and proteins
Water has a high latent heat of vaporization
The heat required to change one mole of liquid at its boiling point under standard atmospheric pressure
44 kJ needed to cause 1 mole water to go from liquid to vapor state
Tensile strength
Ability to resist a pulling force of molecules before breaking their bonds
Cohesion
a molecule is attracted to the same molecule
Adhesion
a molecule is attracted to the other type of substances
Surface tension
the property of liquid surfaces which allows it to resist an external force, due to the cohesive nature of its molecules
How do plants bring water from the roots to the shoots?
Capillary action (Capillarity)
Water potential in Plants
Ability of water molecule to move freely in solution
Measurement of the potential energy in water
Water movement
high to low water potential
Chemical potential
Quantitative expression of the free energy associated with a substance
Water potential consists of 3 components
Solute potential
Pressure potential
Gravity potential
The major factors influencing the water potential in plants
Concentration
Pressure
Gravity
-sign for solute potential
Reduction of the water potential dissolved solutes
Pressure potential
effect of hydrostatic potential
Turgor pressure
+ hydrostatic pressure within cells (pressure potential >0 MPa)
Supports plants cells and tissues
water limitation lowers turgor pressure
Tension
- hydrostatic pressure, frequently develop in xylem
Pressure potential <0 MPa
Gravity potential in plants
plant height is generally to short for gravity potential to make a difference with water potential
Unless it is something tall like trees
Why is water potential important?
Cell growth, photosynthesis and crop productivity are highly influenced by water potential
Scholander pressure chamber
The pressure chamber method for measuring plant water potential
How to pull water through the xylem:
Cohesion, adhesion and surface tension
Water potential
Ability of water molecule to move freely in solution
Important mechanisms for water movement in plants
osmosis “water follows sugar”
Turgor pressure and plasmolysis
Solute potential
The solute potential is reduced when solutes are added to an aqeuous system
Water moves from 0 to negative number
Osmosis
phenomenon of water flow across a semi-permeable membrane
Sucrose cannot pass through the membrane, water moves across membranes
Important for water movement in plants, water borrows sugar, water follows sugar
Equilibrium
Water stop moving across membranes
Water potential =0
Pure water
Resistance of cell wall to deformation
Rigidity of plant cell wall to prevent the osmotic lysis by hydrostatic pressure (turgor pressure)
Plasmolysis
if water is moving out of the cell
Cell Inside: Hypotonic
Cell outside: hypertonic
Plasmolyzed
Water is moving outside of the cell
Solute potential outside of cell < solute potential cell inside
Cell inside: isotonic
Cell outside: isotonic
Flaccid
Solute potential cell outside is equal to solute potential cell inside
Cell inside: hypertonic
Cell outside: hypotonic
Turgid
Water moving into the cell
Solute potential cell outside > solute potential cell inside
Turgor pressure (osmotic pressure)
pressure from fluid within the cell pushing against the cell wall
How do water molecule move across plasma membrane
water channels
How do water molecules go through aquaporins?
Expression of an aquaporin in an Xenopus oocyte accelerates water uptake
Thermodynamic gradients
First response to solute potential gradient
Intermediate response to solute potential gradient
Late response to solute potential gradient
Equilibrium situation
First response to solute potential gradient
Water diffuses from pore orifice
water pulled thru channel by cohesion
Intermediate response to solute potential gradient
Water diffuses from pore orifice
Water pulled thru channel by cohesion
Pressure potential increases in cytoplasm
Late response to solute potential gradient
water diffuses from pore orifice
Water pulled thru channel by cohesion
Pressure potential increases in cytoplasm
Equilibrium situation
Pressure potential increased to balance solute potential
Equilibrium between cells
No NET flux of water across channel
Tetrameric arrangement (tetramer)
each monomer forms a water channel
Phosphorylation and pH
Modify aquaporin channel activity
How to stop osmosis
You need hydrostatic pressure
Diffusion
water movement during transpiration
Transpiration
Evaporation of water mainly through the stomata of leaves
Movement of water in plants (steps)
- Osmosis
- Bulf flow
- Bulk flow
- Diffusion
Diffusion rate is affected by
Area, distance and gradient
Surface tension
Enhancement of intermolecular attractive forces at the surface
Water movement through the leaf
1) Stomata open
2)Water vapor Diffueses from internal air space, down it concentration gradient, into the air
3) Net loss of water vapor causes air-water- interface to recede towards outer microfibrils
3)Establishment of water gradient begins when the air-water-interface touches outer microfibrils
4)H-Bonding/Cohesion transmits tension at surface to bulk water
5) Time dependent buildup of surface tension
6) Water is pulled towards air-water-interface
Analysis of pathway water flow
Apoplasmic (Apoplastic) pathway
Symplasmic (Symplastic) pathway
Transcellular pathway
Apoplasmic (Apoplastic) pathway
Never goes into the plant cell
Water moves through the intercellular spaces (e.g. cell walls) with no entry into cells
No resistance
Symplasmic (symplastic) pathway
First moves into cell through PM
Water moves through the cells via plasmodesmata
Some resistance
Transcellular pathway
Water moves across the plasma membrane
Passes through all of the membranes (vacuole membrane)
Plasmodesmata
microchannel connecting between plant cells through the cell wall, small channel that allows movement through cell walls to other cells
Tracheids
Primitive water-conducting elements
Present in gymnosperms and angiosperms
Cell size species dependent (is small)
Long, thin cells with tapered ends
Walls reinforced with lignin (support)
Gymnosperm
naked seed
Angiosperm
seed is covered
Pit pair
two pits occurring opposite one another in the walls of adjacent tracheid or vessel elements
Vessels
Advanced water-conducting elements
Present only in the angiosperms
One vessel-
Pits
effective combination of primary anf secondary walls
Caviation
a condition where in an air bubble moves into a vessel or tracheids
Embolism
the blocking of a xylem vessel or tracheid by an air bubble or cavity (xylem blocked)
Embolisms spread
from conduit to conduit; a pathway connecting the embolized vessels is shown in yellow
Embolized xylem vessel
No longer hold water
decrease xylem hydraulic conductance
Tensile strength
ability to resist a pulling force of molecules before breaking their bonds
Cohesion theory
the tensile strength of water is high enough to allow water to be pulled through the Treachiary elements
Xylem is vulnerable to
Cavitation (embolism)
Embolized xylem vessel;
no longer hold water
decrease xylem hydraulic conductance
Soil particle size affects
water movement
water retention
Large pore space
Gravitational pull
(sandy soil)
Small pore space
Capillary action
Clayey soil
Saturated soil
All pores are full of water
Gravitational water is lost
After drainage in soil
Field capacity
available water for plant growth
After drying in soil
Wilting point no more water available to plants
The type of soil particle affects
Soil interactions with water
Other factors of soil interaction with water
Organic matter, microbes, salinity, etc
Root architecture
Length of roots, branching, angle
Root architecture is affected by
water flow into roots
Shallow root systems
Effective at catching limited rainfall, things like winter wheat
Hydrotropism
root growth in response to water deficit
Gravity dominates the root growth in
Water sufficient environment
The root can exhibit hydrotropic growth
growth towards water
Osmosis
water uptake from soil to the roots
Root pressure
Positive pressure that forms in the root as the roots uptake water from the soil by osmosis
Apoplasmic pathways
movement through cell walls, except when crossing endodermis
Symplasmic pathway
Movement through cytoplasm and plasmodesmata
Transcellular pathway
water crosses plasma membrane and parallel with movement through plasmodesmata
Epidermis
Production of root hairs which project into the soil increasing surface for water and nutrient uptake
Casparian strip forces
water to cross a plasma membrane
Casparian strip is made of
lignin
Suberin
Cell wall- associated biopolymer found in endodermis
Role of suberized endodermis in the roots
decreasing the water permeability
xylem tensions extending further into the root system
Water movement through the plant like a
tug of war
Radial and axial conductance
importance of water flow through roots
Radial conductance
From soil to stele
Radial conductance is affected by
Anatomy, morphology, cell wall permeability, activity of water channels, etc.
Axial conductance
through the xylem
Axial conductance is affected by;
Number, diameter and structure of the xylem conduits, formation of embolisms etc
Root pressure and guttation
positive pressure is generated by osmosis in the roots
High value of pressure means
high value of tension and a high degree of water stress
Air-water-interface in mesophyll being pushed back to original position
water re-enters cut element
Plant response to water stress depends upon
imposed conditions
genetic background
physiological status
tomato plant subjected to rapidly drying soil
hydropassive response
plant response to water stress varies
with extent of water deficit, rate of dehydration and by genotype
The plant responds to water deficit after
a critical soil water potential is reached
Rate of water deficit and genotype affect
plant response and survival
Osmotic adjustment
a lowering of solute potential due to net solute accumulation in response to drought-stress
Osmotic adjustment for turgor regulation
maintains water absorption and cell turgor in drought conditions
sustain higher photosynthetic rate and expansion growth under drought
Elastic adjustment of cell wall
the relationship between cell volume and turgor
softening
increased cell wall elasticity
delaying the loss of turgor
plant responses to water deficit affect many processes
photosynthesis goes down
stomatal aperture goes down
shoot meristem and leaf growth decreases
root growth increases
solute accumulation increases
water uptake decreases
plants have to balance
their growth and survival responses
Modes of energy exchange
Conduction
convention
latent heat transfer
radiative exchange
Conduction
individual molecules transfer kinetic energy from one to another, but… they do not move far in the process
Convection
individual molecules gain kinetic energy from one regions and themselves transfer it to another region
transport of energy by a volume of fluid (here air)
Latent heat transfer
latent heat of vaporization
water has a very high latent heat of vaporization
radiative exchange
all matter acts as a near perfect black body
high temp
short wavelength, strong emissivity energy
low temp
long wavelength, weak emissivity energy
leaf temperature
energy input= energy output
energy input
short wavelength- radiation from sun (6.28 x 10^4 Joule)
long wavelength- reradiation from soil (3.35)
long wavelength- reradiation from air (1.26)
conduction
direct transfer of heat energy from one body (leaf) to another (surrounding atmosphere: boundary layer)
If plants are under drought stress conditions
stop transpiration by closing stomata, LE approaches zero, leaf temperature begines to rise, eventually a new thermal equilibrium will be established at each leaf surface
Spines
functioning as reflectors and reradiators
Essential element
an element that is needed for completion of life cycle
molecular constituent, without which the plant cannot perform the physiological function necessary to allow development to proceed to maturation
Most fertilizers contain
nitrogen, phosphorus and potassium
Environmental and health problems by using excess amounts of fertilizers
nitrogen fixation is energy demanding
phosphate and potash mining is destructive
eutrophication
nitrous oxide is a major greenhouse gas
Primary macronutrients
nitrogen
phophorus
potassium
Secondary macronutrients
magnesium
sulfur
calcium
Micronutrients
boron
chlorine
sodium
manganese
iron
nickel
copper
zinc
molybdenum
Boron nutrient deficient conditions
discoloration of leaf buds. breaking and dropping of buds
Calcium nutrient deficient conditions
plant dark green, tender leaves pale. drying starts from the tips. Eventually leaf bunds die
Sulphur nutrient deficient conditions
Leaves light green, veins pale green no spots.
Iron nutrient deficient condition
leaves pale, no spots, major veins green
Manganese nutrient deficient conditions
leaves pale in color, veins and venules dark green and reticulated
Copper nutrient deficient conditions
pale pink between the veins, wilt and drop
Zinc nutrient deficient conditions
Leaves pale, narrow and short. veins dark green. dark spots on leaves and edges
Molybdenum nutrient deficient conditions
leaves light green/lemon yellow/orange. spots on whole leaf except veins. sticky secretions from under the leaf
magnesium nutrient deficient conditions
paleness from leaf edges. no spots. edges have cup shaped folds. Leaves die and drop in extreme deficiency
potassium nutrient deficient conditions
small spots on the tips, edges of pale leaves. spots turns rusty. folds at tips
Phosphorus nutrient deficient conditions
plant short and dark green. In extreme deficiencies turn brown or black. Bronze color under the leaf
nitrogen nutrient deficient condition
stunted growth. extremely pale color. Upright leaves with light green/yellowish. Appear burnt in extreme deficiency
Very mobile
N,P,K,Mg
Deficiency symptoms appear first in older leaves and quickly spread throughout the plant
Moderately mobile
S, Cu, Fe, Mn, Mo, Zn,
Deficiency symptoms are normally seen over the entire plant, but the growth rate and rate of nutrient availability can make a considerable difference on the locations at which the symptoms develop
Immobile
B, Ca
Calcium is very immobile
pH
important to nutrient availability, soil microbes and root growth
Bacteria are prevalant in
alkaline (pH>7)
Fungi are prevalent in
acidic (pH<7)
Root growth
5.5 <pH<6.5
Nutrient uptake
Cation exchange capacity (CEC)
cations dissolved in soil water bind to negatively charged soil particles
CEC
degree to which a soil can absorb and exchange ions
plants can free up positively charged nutrients to secrete H+ to exchange with bound cations
Higher CEC
more potential for minerals in the soil
Hoagland nutrient solution
highest possible nutrient concentrations without producing toxicity symptoms
Roots hairs
extensions of root epidermal cells
increasing surface area for absorption
Carnivorous plants
can obtain nutrients by digesting trapped animals
Vascular plants assimilate mineral nutrients mostly
via roots
root developmental responses
cluster roots
biochemical responses roots
root exudates
Nitrogen
the most abundant mineral element in a plant
the most abundant element in the earth’s atmosphere
the 4th most abundant element in a plant after C, H, and O
part of carbon compounds: amino acids, nucleic acids, chlorophyll, etc
If plants are under N-deficient conditions
it progresses
plant stunting
yellowing: lack of chlorophyll
older tissue affected first: N is mobile in plants
Why is nitrogen an essential element?
Forms linkage between amino acids via peptide bond- complex proteins
fundamental to chemical structure of DNA and RNA
Assimilation
incorporation of inoragnic nutrients into organic substances (amino acids, nucleic acids, etc.
N assimilation
GS/GOGAT assimilates inorganic nitrogen into organic molecules
Strategies to improve nitrogen- use efficiency and decrease N pollution
Co-cropping or growing in rotation with legumes enriches soil N content
legumes can acquire N from the atmosphere via special soil bacteria (rhizobia) which are housed in nodules on their roots
Altering flux into amino acid pools or breeding strategies can enhance nitrogen use efficiency
Nitrogen cycle
nitrification, denitrification, nitrogen fixation
roots take up
NO3-(nitrate)
or NH4+(Ammonium)
Nitrogen metabolism
uptake, assimilation and remobilization
Phosphorus
the 1st or 2nd most commonly limiting nutrient for plant growth
The 5th most abundant element in a plant
the 11th most abundant element in the earth’s crust
If plants are under Pi-deficient conditions
stunted in plant growth
abnormal dark green color
older tissue affected first: P is mobile in plants
Reddish purple color: accumulation of anthocyanin pigments
Phosphorus in soil
immobile, insoluble complexes
Arbuscular mycorrhizal (AM) fungi
Facilitator for Pi uptake in most plants
Plant root exudate and microbial exudate
increasing Pi availability
Phosphate transporters
PHT1 for phosphate (Pi) uptake and transport
PHO1
Phosphate (Pi) exporter
moves Pi into xylem: Pi transport to the shoot
Phosphorus cycle
phosphorus (P) is assimilated and used as phosphate (Pi)
Potassium and soidum
the twins but different
both have a single electron in the outer shell: monovalent cations
both are very abundant elements
potassium is an essential nutrient
sodium is toxic
if platns are under K-deficient conditions
substantial growth reduction
yellowing appears on the oldest leaves: K is mobile in plants
brown necrotic lesions develop within the yellow parts and eventually spread to cover the entire leaf blade
Potash
potassium fertilizers are mined from underground reserves
provides K+ for fertilizers
K+ deficiency
rare but plant growth is usually stimulated by additional K+ supply
Potassium is an essential plant nutrient
functions as a counterion for negatively charged molcules, including DNA and proteins: providing stability of dynamic structure for DNA and proteins
Cofactor in some enzymatic reactions
main cation in vacuoles
K+ generates turgor to provide structure: cell expansion, plant growth and plant movement such as regulation of stomatal apertures
Homeostasis
ability of an organism to maintain an internal stability in response to environmental changes
important to the survival of plants
allowing consistency needed to function properly
Why is calcium an essential element
forms a constituent of middle lamella of cell wall: binds neighboring daughter cells together
required at external surface of plasma membrane and tonoplast for membrane integrity
acts as a second messenger in signal transduction
Why is magnesium an essential element
Mg transporters cloned but mechanisms still being elucidated
MG2+ required for: enzyme activities, energy transduction, chlorophyll structure
K+ mobilization
critical for K+ homeostasis
Potassium uptake by
high and low affinity transporters
