Nutrients Flashcards
How can nutrients be classified?
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.)
How are nutrients taken up?
In ionic form (anions, cations)
For algae: diffusion
Bryophytes: through leaves (raindrops)
Vascular plants: establishment of sophisticated root system
Correlation btw. amount of fertilizer (N, K, P) and yield
Linear
Mining for fertilizers
Phosphate and potassium reserves are geologically biased and finite reserves
Problems with fertilizers
High energy consumptive production, finite resources, eutrophication (algal blooms)
How do ions travel in the plant?
Apoplast/symplast/transmembrane path
Selection process at endodermis (casparian strip) => regulation of ion transport
Root differentiation
Along vertical axis
No casparian strip in tip of root
Then lignified casparian strip, allows selective water flow
Then suberinized, no water inflow/outflow
Suberinization
Dynamically responds to environmental stresses through hormones
ABA => more suberin
Ethylene => less suberin
Electrochemical gradient in root
Influx of cations
Efflux of anions
Bc. ca. -150mv in cell
Nernst equation
∆E = 60mv log(cext/cint)
At ∆E = 60mv the concentration difference is around 10x
Driver of coupled transport in plants
H+
How are proton gradients established?
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
Where are proton transporters located?
In plasma membrane or tonoplast (membrane of vacuole)
Potassium (K)
Strengthens cell walls
Promotes stress tolerance
Regulates enzyme activities
cofactor
Counterion for negatively charged DNA
Cell expansion (guard cells)
maintains turgor and reduces wilting
K deficiency
Leads to chlorotic lesions in leaves => yellowing from outside
Potash mining
Pump water in soil => let evaporate in lakes
K transporters
Multiple different families
Symporters and antiporters
Multi-sensory guard cell model
Open:
Light
Low CO2
High humidity
Auxin, JA-mimic
K influx
Close:
Low light
High CO2
Low humidity
ABA
K efflux
Ca2+ influx
Salinity stress
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
Salinity tolerance mechanisms
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
Sensing of salt stress
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
Halophytes vs. Halotolerants
Preferentially live in saline environments vs. can tolerant salt stress
Nitrogen
Abundant in atmosphere but hard to acquire for plants
Triple bond in N2 has to be reduced to ammonia (NH3)
Haber-Bosch
Industrial “fixing”/reducing of N2 to NH3/NH4 (ammonia/ammonium)
Very energetically demanding
Preferred form of nitrogen for uptake in plants
Nitrate (NO3-) => reduction to NO2- by nitrate reductase (& co-factors = micronutrients) => reduction to NH4+
Assimilation of ammonium
Glutamine by glutamine synthetase
Glutamate by glutamine-2-oxoglutarateaminotransferase
Incorporation into amino acids and other nitrogen containing molecules => recycling (pool of nitrogen)
Nitrate and Ammonium transporters
AMT and NRT
HATs (high affinity transporters) and LATs (low affinity transporters)
Also amino acid transporters and urea transporters
Discovery of nitrate transporters
Chlorate herbizide => uses nitrate transporters
Many prokaryotes can fix nitrogen using an enzyme called…
Nitrogenase using 16 molecules of ATP
Root nodules
Leghemoglobin
Bacteria needs anoxic environment, leghemoglobin buffers oxygen
Nitrogenase complex
Responses to nitrogen deficit
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
Perception of nitrogen deficit
Not fully understood, signalling by small peptide => activates receptor kinase => signal to other part of plant => growth?
Phosphorous
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
Optimizations for phosphate acquisition
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
Phosphate starvation responses
Local:
Root growth (primary, lateral and root hairs)
Systemic:
Pi transport, recycling and recovery (favour certain compounds over others)
P-transporters
PHT (phosphate transporters) => (PO4)3-
H+/Pi co-transporters that have 12 transmembrane domains
Phosphate sensing
Phosphate uptake symbiosis with microorganisms
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
