Assimilation of Inorganic Nutrients - 8 Flashcards
Define Nutrient Assimilation
energy-requiring process which plants incorporate inorganic nutrients into the carbon constituents necessary for growth and development
What does acquiring nitrogen from the atmosphere require (nitrogen fixation)
breaking the stable triple covalent bond between two nitrogen atoms to produce ammonia or nitrate
Define the Haber-bosh process
is the starting point for the manufacture of many industrial and agricultural products (including nitrogen fertilizers)
How is ammonia formed
N2 combines with hydrogen to form ammonia, under elevated temperatures and high pressure in the presence of a metal catalyst (usually iron)
What are the 3 processes that fix 190 million metric tons per year of nitrogen
- lightning
- photochemical reactions
- biological nitrogen fixation (90%)
Once fixed into ammonia or nitrate…
nitrogen enters biogeochemical cycle through several organic and inorganic forms before returning to molecular nitrogen
at high concentrations, ____ is toxic to living tissues, while ____ can be safely stored and translocated in plant tissues
ammonium
nitrate
Explain nitrate assimilation
plant roots absorb nitrate from soil solution, and assimilate most into organic nitrogen compounds
Define nitrogen reductase
main molybdenum-containing protein in vegetative tissues. it catalyzes first step in nitrate assimilation
what influences nitrate reductase at the transcription and translation level
nitrate, light and carbohydrates
nitrate reductase is also subject to _____ involving a reversible phosphorylation
post-translational modification
What inactivates nitrogen reductase
darkness and Mg 2+
what provides the highest amount of regulation of nitrate reductase activity
phosphorylation and dephosphorylation provides rapid control
Function of nitrite reductase
converts nitrite into ammonium, highly reactive
What happens after plants generate nitrite generated from nitrate reduction
it is transported from the cytosol to the chloroplasts and plastids (leaves and shoots)
Where is nitrite reductase encoded and synthesized
encoded in nucleus
synthesized in cytoplasm with N-terminal transit peptide
What induces transcription of nitrite reductase
elevated concentrations of nitrite or exposure to light
nitrate is reduced primarily in the ______, as supply increases nitrate is translocated to the ____
roots
shoots
how do plants cells amount ammonium toxicity
by rapidly converting the ammonium generated from nitrate assimilation or photorespirations in amino acids
The primary pathway of ammonium assimilation involves the sequential actions of _____ and _____
glutamine synthetase and glutamate synthetase
Define glutamate synthetase (GS)
combines ammonium with glutamate to form glutamine
involves divalent cation and ATP
Where are the two classes of GS located in plants
and which is more affected by carbs and light
one in cytosol and one in plastids
plastid
elevated levels of ____ stimulate the activity of glutamate synthetase
glutamine - two forms
in non-photosynthetic tissue and in photosynthetic tissues
Define glutamate dehydrogenase (GDH)
catalyzes a reversible reaction that synthesizes or deaminates glutamate
