Nutrients

Question 1

How can nutrients be classified?

Answer 1

According to the (relative) amount in the plant => Macro- or micronutrients or their function (Phophate and Nitrogen in essential compounds such as ATP and nucleic acids, ions that regulate efflux/influx of water (into stomates for example), etc.)

Question 2

How are nutrients taken up?

Answer 2

In ionic form (anions, cations)

For algae: diffusion

Bryophytes: through leaves (raindrops)

Vascular plants: establishment of sophisticated root system

Question 3

Correlation btw. amount of fertilizer (N, K, P) and yield

Answer 3

Linear

Question 4

Mining for fertilizers

Answer 4

Phosphate and potassium reserves are geologically biased and finite reserves

Question 5

Problems with fertilizers

Answer 5

High energy consumptive production, finite resources, eutrophication (algal blooms)

Question 6

How do ions travel in the plant?

Answer 6

Apoplast/symplast/transmembrane path
Selection process at endodermis (casparian strip) => regulation of ion transport

Question 7

Root differentiation

Answer 7

Along vertical axis
No casparian strip in tip of root
Then lignified casparian strip, allows selective water flow
Then suberinized, no water inflow/outflow

Question 8

Suberinization

Answer 8

Dynamically responds to environmental stresses through hormones
ABA => more suberin
Ethylene => less suberin

Question 9

Electrochemical gradient in root

Answer 9

Influx of cations
Efflux of anions
Bc. ca. -150mv in cell

Question 10

Nernst equation

Answer 10

∆E = 60mv log(cext/cint)

At ∆E = 60mv the concentration difference is around 10x

Question 11

Driver of coupled transport in plants

Answer 11

H+

Question 12

How are proton gradients established?

Answer 12

PM H+-ATPase uses ATP to pump H+ out of cell (monomeric)
VH+-ATPase pumps protons into vacuole (multimeric)
H+-PPase uses pyrophosphate as energy source to pump protons

Question 13

Where are proton transporters located?

Answer 13

In plasma membrane or tonoplast (membrane of vacuole)

Question 14

Potassium (K)

Answer 14

Strengthens cell walls

Promotes stress tolerance

Regulates enzyme activities

cofactor

Counterion for negatively charged DNA

Cell expansion (guard cells)
maintains turgor and reduces wilting

Question 15

K deficiency

Answer 15

Leads to chlorotic lesions in leaves => yellowing from outside

Question 16

Potash mining

Answer 16

Pump water in soil => let evaporate in lakes

Question 17

K transporters

Answer 17

Multiple different families

Symporters and antiporters

Question 18

Multi-sensory guard cell model

Answer 18

Open:

Light
Low CO2
High humidity
Auxin, JA-mimic
K influx

Close:

Low light
High CO2
Low humidity
ABA
K efflux
Ca2+ influx

Question 19

Salinity stress

Answer 19

Na+ and K+ chemically similar, but Na is toxic => osmotic stress, oxidative stress, compete for high affinity K+ transporters, cause protein degradation and membrane destabilization

Question 20

Salinity tolerance mechanisms

Answer 20

Limit influx => leads to K-deficiency (chlorosis)

Pump out/compartmentalize Na

Synthesize solutes for osmotic adjustment

Accumulate K, to maintain high K/Na ratio

Extrude Na through salt glands

Prevent Na from moving into shoots/leaves => K-deficiency

Change development of shoot

Question 21

Sensing of salt stress

Answer 21

SOS pathway (salt overly sensitive)

SOS3 = calcineurin B-like protein CBL4

SOS2 = CBL interacting protein kinase CIPK24

SOS1 = Na+/H+ antiporter

signalling depends on rapid influx of calcium

Question 22

Halophytes vs. Halotolerants

Answer 22

Preferentially live in saline environments vs. can tolerant salt stress

Question 23

Nitrogen

Answer 23

Abundant in atmosphere but hard to acquire for plants

Triple bond in N2 has to be reduced to ammonia (NH3)

Question 24

Haber-Bosch

Answer 24

Industrial “fixing”/reducing of N2 to NH3/NH4 (ammonia/ammonium)

Very energetically demanding

Question 25

Preferred form of nitrogen for uptake in plants

Answer 25

Nitrate (NO3-) => reduction to NO2- by nitrate reductase (& co-factors = micronutrients) => reduction to NH4+

Question 26

Assimilation of ammonium

Answer 26

Glutamine by glutamine synthetase

Glutamate by glutamine-2-oxoglutarateaminotransferase

Incorporation into amino acids and other nitrogen containing molecules => recycling (pool of nitrogen)

Question 27

Nitrate and Ammonium transporters

Answer 27

AMT and NRT

HATs (high affinity transporters) and LATs (low affinity transporters)

Also amino acid transporters and urea transporters

Question 28

Discovery of nitrate transporters

Answer 28

Chlorate herbizide => uses nitrate transporters

Question 29

Many prokaryotes can fix nitrogen using an enzyme called…

Answer 29

Nitrogenase using 16 molecules of ATP

Question 30

Root nodules

Question 31

Leghemoglobin

Answer 31

Bacteria needs anoxic environment, leghemoglobin buffers oxygen

Question 32

Nitrogenase complex

Question 33

Responses to nitrogen deficit

Answer 33

Increase uptake by:
Activation of NO3- and NH4+ transporters
Increased root growth, specifically in areas of high [N]
Decrease use by:
Recycling N from e.g. chlorophyll (shortened leaf senescence)
Decrease accumulation of N-rich chlorophyll
Smaller pools of N-containing compounds
Accumulation of N-free compounds

Question 34

Perception of nitrogen deficit

Answer 34

Not fully understood, signalling by small peptide => activates receptor kinase => signal to other part of plant => growth?

Question 35

Phosphorous

Answer 35

Part of nucleic acids, membranes (phospholipids) and ATP => energy

No atmospheric pool

Plant can only acquire Pi and only in close proximity to the root

Question 36

Optimizations for phosphate acquisition

Answer 36

Favor lateral root growth close to soil surface (reduced gravitropism)

But: energetically expensive => reduce metabolic processes within this root system, increase aerenchyma

Proteoids: cluster roots

Question 37

Phosphate starvation responses

Answer 37

Local:

Root growth (primary, lateral and root hairs)

Systemic:

Pi transport, recycling and recovery (favour certain compounds over others)

Question 38

P-transporters

Answer 38

PHT (phosphate transporters) => (PO4)3-

H+/Pi co-transporters that have 12 transmembrane domains

Question 39

Phosphate sensing

Question 40

Phosphate uptake symbiosis with microorganisms

Answer 40

Ectomycorrhizal fungi (outside of root and btw. cells) => less common => trees
Endomycorrhizal fungi => Arbuscular mycorrhiza protrude cells, but don’t destroy membrane
Both increase uptake surface