BB30129: Nitrate Signalling (Hans)
Nitrate
Nitrogen is required for generating various essential molecules:
chlorophyll, proteins, nucleic acids, ATP and metabolites.
Nitrogen frequently limits plant growth – nitrogen-deficient corn
crop display chlorosis, necrosis, stunting
Nitrate is the major source of nitrogen in soils.
Nitrate concentration in soils varies from ~5uM to 50mM, in time
and space
Plants forage for some nutrients (such as nitrate) by altering their
growth and metabolism
Nitrate is not only an essential nutrient but also an environmental
signal – even if a plant is not deficient in nitrogen, the importance of
nitrate as a nutrient means that the plant can still respond to it.
Nitrogen fertilisers are widely used with the aim of enhancing plant
growth, however only 30-50% of nitrate applied is successfully
taken up by the plant. Improving nitrogen signalling would promote
nitrate uptake by plants (both endogenous soil nitrate and nitrogen
fertilisers)
, Nitrate uptake + reduction (local signalling)
Examples of nitrite uptake:
Pitcher plants trap ants and assimilate the nitrate from their
decomposition by growing its own roots down into the pitcher.
Other Dischidia species have modified leaves that house ant
colonies. Roots grow into these leaves, assimilating nitrogen and
carbon.
Foliar nitrate uptak: epiphytes assimilate nitrogen through their
leaves and roots.
Signalling pathway:
Nitrate uptake occurs in root epidermal & cortical cells, and also in
leaves.
Transported into cell
alongside 2 H+ ions
(protons) by nitrate
transporters which are
driven by membrane
potential.
High & low-affinity
transporters allow plants
to take up nitrate under a
wide range of external
concentrations
Cytoplasmic nitrate can
then be:
a) taken up and stored in
the vacuole
b) released extracellularly
c) reduced to ammonia by
cytoplasmic nitrate
reductase and plastid
nitrite reductase.
Important that this process works efficiently to prevent build up of
toxic nitrate forms.
Local root responses to nitrate involve NRT1.1
transporter
Arabidopsis microarray has identified ~1000 nitrate-inducible genes
(10% of all Arabidopsis genes). Many are involved in carbon &
nitrogen metabolism.
Primary nitrate response = no protein synthesis required, signalling
cascade triggered within minutes of altered nitrate conditions, and
Nitrate
Nitrogen is required for generating various essential molecules:
chlorophyll, proteins, nucleic acids, ATP and metabolites.
Nitrogen frequently limits plant growth – nitrogen-deficient corn
crop display chlorosis, necrosis, stunting
Nitrate is the major source of nitrogen in soils.
Nitrate concentration in soils varies from ~5uM to 50mM, in time
and space
Plants forage for some nutrients (such as nitrate) by altering their
growth and metabolism
Nitrate is not only an essential nutrient but also an environmental
signal – even if a plant is not deficient in nitrogen, the importance of
nitrate as a nutrient means that the plant can still respond to it.
Nitrogen fertilisers are widely used with the aim of enhancing plant
growth, however only 30-50% of nitrate applied is successfully
taken up by the plant. Improving nitrogen signalling would promote
nitrate uptake by plants (both endogenous soil nitrate and nitrogen
fertilisers)
, Nitrate uptake + reduction (local signalling)
Examples of nitrite uptake:
Pitcher plants trap ants and assimilate the nitrate from their
decomposition by growing its own roots down into the pitcher.
Other Dischidia species have modified leaves that house ant
colonies. Roots grow into these leaves, assimilating nitrogen and
carbon.
Foliar nitrate uptak: epiphytes assimilate nitrogen through their
leaves and roots.
Signalling pathway:
Nitrate uptake occurs in root epidermal & cortical cells, and also in
leaves.
Transported into cell
alongside 2 H+ ions
(protons) by nitrate
transporters which are
driven by membrane
potential.
High & low-affinity
transporters allow plants
to take up nitrate under a
wide range of external
concentrations
Cytoplasmic nitrate can
then be:
a) taken up and stored in
the vacuole
b) released extracellularly
c) reduced to ammonia by
cytoplasmic nitrate
reductase and plastid
nitrite reductase.
Important that this process works efficiently to prevent build up of
toxic nitrate forms.
Local root responses to nitrate involve NRT1.1
transporter
Arabidopsis microarray has identified ~1000 nitrate-inducible genes
(10% of all Arabidopsis genes). Many are involved in carbon &
nitrogen metabolism.
Primary nitrate response = no protein synthesis required, signalling
cascade triggered within minutes of altered nitrate conditions, and
