PB 250 Exam 3: Plant Nutrition, Transport and Phytohormones

what do plants require? (4)

CO2, H2O, light energy and inorganic nutrients from environment

definition of essential nutrient for plant

it cannot complete its life cycle without them

micro and macro nutrients are classified based on...

the amount present in plant tissues

what are the three principal structural elements of plants?

C, H, and O

C, H, and O account for ___% of a plant's mass

96

What is phytoremediation?

plants help to clean toxic sites by uptake of heavy metals

what are the principal nutrient-absorbing structueres of a plant?

roots

assimilation in plants

apoplastic and symplastic pathways

apoplastic pathway

water and dissolved minerals diffues into the epidermal cells into the cortex

symplastic pathway

minerals cross root hair membrane and diffuse from cytoplasm to cytoplasm toward the stele

nitrogen fixation

Process of converting nitrogen gas (N2) into ammonia (NH3) or NH4+

- reduction

nitrification

the oxidation of N2 to NH3 or NH4+ to nitrite and nitrate

NH3 is

ammonia

NH4+ is

ammonium ion

NO2- is

nitrite

NO3- is

nitrate

what does nitrogen fixation?

bacteria and cyanobacteria

two enzymes that make up nitrogenase

dinitrogenase reductase and dinitrogenase

what determines if a plant can use a mineral (4)?

availability, binding vs leaching, assimilation, rhizosphere interactions

what is the industrial nitrogen fixation process called?

Haber-Bosch process

how does the Haber-Bosch process work?

N2 and H2 combined under high temp and pressure in the presence of a catalyst

the nitrogen fixation step is a oxidation/reduction rxn?

reduction

what do plant roots secrete to attract bacteria?

phenolic compounds

what is inhibitory to nitrogenase?

oxygenase

what is the importance of leghemoglobin?

it binds oxygen and controls oxygen levels within nodule cells and deliver O2 to bacterioids

most of phosphorus on earth is stored in

sediments and rock

plant strategies for improving phosphorus availability (3)

- root exudates (H2O, carboxylic acid, phosphatases) to enhance uptake

- cluster roots

- mycorrhizal associations

ectomyccorhizae grow how?

between root cells down to the endodermis

endomyccorhizae grow how?

between and inside cells down to the endodermis

what form must N2 be converted in order to be accessible to plants?

NH4+ or NO3-

what enzyme catalyzes N2 fixation?

nitrogenase

how much ATP does nitrogenase need to fix N2?

18 per nitrogen fixed

what is the major source for fertilizer?

mining of phosphate-containing rocks

what is translocation?

solute movement through phloem

does translocation move up or down?

down

translocation is a ______ stream

assimilate

what hypothesis explains translocation?

pressure flow hypothesis (Munch hypothesis)

what is transpiration?

water movement through xylem

does transpiration move up or down?

up

transpiration is a ______ stream

transpiration

what hypothesis explains transpiration?

cohesion-tension theory, cohesion-adhesion theory, transpirational pull

what is adhesion?

attraction between unlike molecules

what is cohesion?

attraction between like molecules due to hydrogen bonding

what are the three possible pathways for water movement through plants?

apoplastic, symplastic, and transcellular

apoplastic water movement

movement between cells and along cell walls

symplastic water movement

movement from cell to cell via plasmodesmata

transcellular water movement

movement through the membranes of cells, not necessarily through plasmodesmata

what happens if there is a break in the water column? cavitation?

perforation plates are set to trap embolisms, and pits which allow the by-pass of a blocked tracheary element

what forms the water channels in plants?

tracheary elements

what is an embolism?

air bubbles that form in the water column

what is the driving force of water transport in plants?

- cohesion of water molecules to eachother

-adhesion of water molecules to walls of vessel elements, resisting downward movement

- pull of evaporation from stomata

what kind of pressure is associated with translocation?

positive

what kind of pressure is associated with transpiration?

negative

when there is an increase in sugar content, water moves into the ______________ during translocation

sieve tube elements

turgor pressure is highest in the...

initial sieve tube element

what do phytohormones regulate?

cell division, elongation and differentiation

- also pattern formation, organogenesis, reproduction, sex determination and responses to stress

What does pleiotropic mean?

influence many traits

wide ranging effects

hormone steps

initial sensor, synthesis, transport, perception/receptor, signaling and responses

auxin

-promotes cell elongation, root formation and bud growth

- phototropism and gravitropism

what ways can hormones be made?

isoprenoid, amino acids, and lipids

the auxin hormone blocks the formation of what?

lateral branches

how do phytohormones move?

through the phloem or transporter proteins

auxin travels (transport)

down, from tip of shoot to tip of root

what is basipetal transport?

when auxin changes direction and moves short distances up the root again

what was the first experiment to discover auxin?

Darwin & Darwin

at low auxin levels, what happens? (signaling pathway)

Aux/IAA proteins and ARF protiens associate and interfere with ARF action, inhibiting transcription

the majority of phytohormones are

small organic molecules

what was the first phytohormone to be discovered?

auxin

at high levels of auxin...

Aux/IAA proteins associate with SCF complex, leading to proteolysis

- stops them from interfering with ARF protien

what does gibberellins do?

inhibits growth inhibitors

- seed germination, flowering, fruit growth, sex determination

gibberellins was first identified in...

fungal compounds

what do DELLA proteins do?

inhibit growth by blocking transcription

gibberellins triggers DELLA protein....

proteolysis

cytokinin functions

- cell multiplication and maintenance of shoot meristem

- also control of leaf senescence and nutrient allocation

how do auxin and CK act antagonistically?

auxin promotes root branching and CK promotes shoot branching

- CK promotes stem cell fate at SAM, auxin promotes lateral organ at SAM

- CK promotes differentiation at RAM, auxin maintains stem cell fate at RAM

ethylene promotes

senescence of leaves and petal

fruit ripening

abscisic acid

- stress responses

- control of stomatal aperture

what hormone accumulates in maturing seeds?

ABA

what hormone contributed to the evolution of drought tolerance in land plants?

ABA

seed germination requires the production/synthesis of what hormone?

GA

seed germination requires the catabolism/elimination of what what hormone?

ABA

what is the first downstream event from the binding of auxin or gibberellin to the respective receptors?

protein destruction

what hormones are known as inhibitors of an inhibitor?

auxin and GA

what hormones promote cell division and growth of the fruit?

auxin and GA