16. Assimilation of Nitrogen Flashcards
nitrogen is the __ most abundant element in a plant
4th
plants use only 2 forms of N:
NH4+ (ammonium) and NO3- (nitrate)
3 main ways nitrogen enters biosphere:
biological fixation
anthropogenically (haber-bosch process)
lightning - atmosphere
why is haber-bosch process important?
accounts for 50% of all nitrogen fixation globally, but also 2% of all FF consumption
allowed for an agricultural boom, green revolution, fertilizers, allows agricultural production necessary for supporting world pop.
also, requires a LOT of energy
N2 has a ___ bond, which means:
triple ; it is very difficult to break, requires huge input of energy
atmospheric N becomes bioavailable
N2 + ___ –> ___
N2 + 3 H2 –> 2NH3
biological fixation of N is only possible in:
prokaryotes
2 types of bacteria impt for N assimilation:
rhizobia
actinobacteria
rhizobia have a symbiosis with:
legumes
actinobacteria have a symbiosis with:
actinorhizal plants
examples of legumes
soybeans, peas, lentils, alfalfa
N assimilating bacteria form:
nodules on roots
enzyme responsible for N assimilation
nitrogenase
nitrogenase is tricky because:
it is inhibited by O2
how do bacteria get around oxygen inhibition?
leghemoglobin binds to oxygen and carries oxygen away from nitrogenase
leghemoglobin
myoglobin-like protein that binds to oxygen and transports it away from nitrogenase towards bacteroids that use it for respiration
peribacteroid membrane
permeable barrier that separates respiring symbiotic cells and nitrogenase to maintain proper oxygen levels
what causes the meaty taste in impossible burgers?
leghemoglobin
5 steps in the formation of a nodule
- communication between bacteria and root hair
- root hair curling around bacteria
- infection thread formation, bacteria spreads throughout root hair
- cell division in root
- leghemoglobin expressed in nodule
