Crop Phys - Nitrogen Fixation/Growth/Hormones Quiz

nitrogen fixation

• conversion of molecular nitrogen to ammonium

• can occur through lightning, industrial N fixation and biological N fixation

three types of biological N fixation

• symbiosis

• associations

• free living

symbiosis

• energy source: sucrose and metabolites form host plant

• ex- rhizobium

• fixes 50-400kg

• legumes

associations

• energy source: root exudates from host plant

• fixes 10-200kg

• ex- azospirillum

free living

• energy source

  • heterotroph: plant residue

  • autotroph: photosynth

• ex- azobacter

nitrogenase complex

• uses reducing power to convert atmospheric nitrogen gas into ammonia

• only catalyzed by bacteria/prokaryotes

• req a lot of reducing power and atp

• plant provides carbon source

• N2 is triple bonded, hard to break

3 major steps of symbiotic association formation

• signaling

• infection

• nodule development

Signaling

• release of elicitors by plant roots

• chemoattractants (attracts rhizobia)

• nod genes (produced by bacteria)

• confirms compatibility by making interactions specific to certain plants and bacteria

molecules involved in signlaing

• flavonoids and isoflavonoids

  • ex- luteolin (alfalfa, nod gene inducer)

  • ex- genistem (soybean, nod gene inducer)

• betaines and aldonic acids

nod factors

• bacterial products that act as morphogens to induce nodulation in the plant

• molecules involved, lipochitooligosaccharides (LCOs), lipids and carbs, hormones, nodulation outer proteins

• plants recognized very low nod factor concentration

• perceived by plants via nod factor receptor kinases

signaling and host specificity in rhizobia

• root produces chemoattractants/elicitors into the soil

• rhizobia in the rhizosphere recognize elicitors, their nod gene is activated

• rhizobia produces and releases nod factors into the soil

• plant recognizes nod factors via receptors

infection thread

• a tunnel built by the plant for the bacteria to move into

• formed within 18-30h of plant recognizing nod factors

determinate nodules

• soybeans

• nodule develops at roughly the same rate

• have a set end and are not meristematic, cannot grow indefinitely

• spherical in shape

nodule primordia

• in crop legumes, initiated opposite to protoxylem poles

• indeterminate → w/in inner root cortex

• determinate → w/in outer root cortex

indeterminate nodule

• alfalfa and peas

• have meristem region and can keep growing

• oval/oblong in shape

• have 3 regions, 1 with new cells forming, 1 with cells doing the fixation, and 1 with cells senescing

transfer of fixed N into host

• nh3 diffused out of bacteroid into the symbiosome and is protonated to NH4+ due to low pH of symbiososome

• nh4 transported across peribacteroid membrane and into the cyotplasm of the infected cell, where they can be used

determinate N exporting

• nh3 assimilated into glutamine, then xanthine that moves into uninfected cells where ureides are produced and exported via xylem

indeterminate N exporting

• nh3 made into glutamine, then asparagine which is used for export

oxygen permeability barrier

• layer of empty cells, reduces rates of oxygen penetration into nodule core

leghemoglobin

• high oxygen affinity

• controls availability of free oxygen in infected cells to limit nitrogenase inhibition

• creates the red color of the rhizobia

tissue

• a group of similar cells doing the same job

organ

• different types of tissue (ex- leaf)

growth

• irreversible change

• a positive change over a period of time

• usually quantitative

differentation

• functional changes

• qualitative change

development

• growth and differentiation

• overall changes that a plant undergoes through its life cycle

• ex- seed germ, flower formation, fruit formation, etc.

types of growth

• cell division and expansion

• increase in dry weight

Protoderm

• forms epidermis

primary meristems

• protoderm

• ground meristem

• procambium

ground meristem

• forms pith, cortex, and mesophyll

cortex

• forms cork cambium, which makes periderm

procambium

• forms primary phloem and xylem as well as vascular cambium (which then forms secondary xylem and phloem

phytomer

• a unit consisting of a leaf, a node, an internode, and an axillary meristem

intercalary meristem

• present in grasses

• meristem at base of the leaf sheath, leaf blade, and intersection of node and internode

root zones

• root apical meristem

• elongation zone

• maturation zone

cellulose

• arranged in microfibrils in cell wall

• primary cell wall component

• synthesized at the plasma mem

primary cell wall components

• cellulose

• hemicellulose (ex- xyloglucan, arabinoxylan, etc)

• pectin

diffuse growth

• entire cell as a whole expands at the same rate

cell tip growth

• one side of the cell expands

• expansion is unequal

• ex- root hairs, pollen tubes

acid induced growth

• cell walls extend much faster at an acidic ph rather than a neutral ph

• mediated by expansins

creep

• time dependent irreversible extension, typically the result of slippage of wall polymers relative to one another

plant cell expansion steps

• osmotic uptake of water across the plasma mem is driven by the gradient in water potential

• turgor pressure builds because of cell wall rigidity

• biochemical wall loosening occurs, allowing the cell to expand in response to turgor pressure

phyllochron

• rate of appearance of successive leaves (or phytomers)

• when the leaves appear visually, not when they are created

plastochron

• rate of initiation of successive leaves

cell death

• localized process that culminates in the death of the cell and is often quite rapid

• ex - hypersensitive response

senesence

• slower, systemic process that includes nutrient remobilization and under most conditions, culminates in the death of cells

• ex- deciduous trees shedding leaves in autumn

programmed cell death

• a developmental program in many tissues

• ex- tracheary cells, arenchyma formation, leaf senesence, sepal and petal senesence

hormones/phytohormones

• naturally occurring substance which influences physiological processes at low concentration

factors influencing hormone effects on tissues

• biosynthesis

• catabolism

• compartmentation

• transportation

• modulation/modification

• sensitivity of the tissue to the hromone

auxin major functions

• cell elongation

• tropism (photo, gravi, and thigmo)

• regulation of developmental affects

  • apical dominance, floral bud development, leaf abscission, lateral root formation, vascular differentiation, fruit development

auxin synthesis

• synthesized in meristem and young dividing tissue, especially SAM and young leaves

basipetal

• movement from shoot tip to base of the plant (area b/t shoot and root)

acropetal

• movement from base to root apex

auxin transportation (cellular level)

• transport proteins at the end/base of the cell, not on side or top

• establish gradient of auxin movement in vascular tissue

• auxin moved into apoplast, depending on pH, apoplast is protonated or not

  • not protonated → diffuse through membrane

  • protonated → co transported with protons into the cell

• eflux carriers move auxin out of bottom of the cell

• largely active transportation

phototropism

• growth in response to light

• auxin is distributed on the far side of the light source, causing higher rates of cell elongation on one side, forcing the shoot to bend towards the light

gravitropism

• growth in response to gravity

• auxin is redistributed to cause cell elongation on one side, forcing the plant to grow upright

• ex- goosenecking in corn

auxin in roots

• inhibits growth/elongation in main axis of root/root tip

• moves to root from synthesis in the shoot via phloem

statoliths

• starch granules within the root cap

statoliths when root growing straight down

• uniform distribution of auxin via the stele

statoliths when root is horizontal

• statoliths fall and press on one side of the cells, causing auxin to move to other side of the root, inhibiting elongation and causing the root to bend as elongation is increased on one side vs the other

apical dominance

• auxin suppresses growth of axillary/lateral buds

• when the terminal bud/apical meristem is removed, the suppression is subsided and the axillary bud will grow

strawberry achenes

• achenes in strawberries (seeds) cause the receptacle to swell and form the fruit

• when achenes are removed, receptacle does not swell as much

• but if supplemented with auxin (achenes removed) the receptacle swells

cytokinin function

• promote cell divison in the shoot

• regulate auxin action and distribution

• delay leaf senesence

• promote nutrient movement

• involved in formation of N fixing nodules in legumes

cytokinin cell division in sam and ram

• promote shoot growth by increasing cell proliferation in the SAM

• inhibit root growth by promoting exit of cells from the RAM, keeping the meristem cell number small

cell proliferation

• increased production of cells in the meristem

auxin vs cytokinin in the SAM

• auxin promotes differentiation into lateral organs/organ initiation

• cytokinin increases cell proliferation, promoting stem cell fate

auxin vs cytokinin branching in SAM

• auxin inhibits branching

• cytokinin promotes branching

auxin vs cytokining root branching

• auxin promotes branching

• cytokining inhibits branching

cytokinin oxidase

• inactivates cytokinin

axillary buds and auxin vs cytokinin

• auxin produced in apical bud inhibits axillary bud growth by turning off cytokinin biosynthesis and turns cytokinin oxidase on, reducing cytokinin concentration

• if apical bud is removed, no flow of auxin turning off genes

• so then cytokinin biosynth gene is turned on and cytokinin oxidase is turned off, leading to axillary bud growth