L5- Grand challenges nitrogen use Flashcards
how do plants get N
nitrogen is needed for amino acids, proteins and other cellular constituents. Nitrogen is needed for amino acids, proteins and other cellular consituents, notrogen dficiency results in stunted growth and chlorotic leaves, N is generally the most limiting nutrient to plant growth
ammonia is the point of entry of nitrogen into organic molecules, it is generated in two ways
1- reduction of nitrate (predominant form of soil N) to ammonia N03- NH3
2- reduction of N2 by micro-orgnaisms often in symbiotic association with plants N2 - NH3
nitrate reduction accounts for about 20000 mt per annum, compared with N2 fixation at 200mt
what is industrial harber bosch
process of making 2NH3, N2 + 3H2 -> 2NH3
requires high temp, high pressure and has low yield
- uses 1-2% of global energy, 85% of ammonia produced goes to make fertiliser
- fertiliser use is highest in europe, china some countried in S america
how do micro organisms fix nitrogen
250 species of micro-organisms (bacteria and cyanobacteria) fix nitrogen
-they do this difficult chemistry (biological haber-bosch process with the aid of the nitrogenase enzyme
-can be free living in soil, or associated with plants (usually legumes)
what are the three major issues for nitrogen fixation
- reaction is v sensitive to oxygen (inactivates nitrogenase)
-requires a very large input of energy in the form of ATP and reductant
-side reaction- the reduction of 2H+ to H2
how do legumes use 100 C atoms
1/3 go to nodules:
5C for growth
12C for production of ATP and NADH to fix N
15C to provide carbon for the assimilation of NH3
what is the process of symbiotic relationship with bacteria
1- root hair from an infection thread by invagination of the plasma membrane
2- rhizobium bacteria penetrate the infection thread, and form bacteriods within vesicles
3- root cells grow around a bacteroid forming a nodule
4- the nodule develops vascular tissue that facilite the exchange of materials between bacteria and plant
why are genes important
genetics, singalling are important for symbiotic relationship between bacteria and plant
nextgen sequencing allows large-scale comparative genomic analysis
- allows tracing of when phenotype traits are lost/gained
-identify key genes (TFs) underpinning these changes, lead for engineering in crops
genes/signals identified required for bacterial/plant interaction
evolutionary conservation with other plant/microbe interactions
genes/signals identified for nodule formation
evolutionary conservation with lateral root formation
how do plants differentiate between main foot and lateral root
during lateral root formation, pericycle cells are triggered to undergo cell division, and burst out side of root
pericycle generates new lateral roots which allow the plant to explore the environment and anchor the plant, activation of the pericycle links development to the environment
PIN-mediated auxin flux is what dictates lateral root formation, auxin can be engineered to accumulate in certain areas
this is done by auxin being a weak acid, this means ti can form protonated and deprotonated forms, this is deopendent on the pH, lots of protons / very acidic will be protonated form, ionised form is membrane impermeable so cant move out of cell, PIN proteins allow auxin to move out, these direct auxin out at specific directions
lateral root and nodules show extensive overlap in organogenesis and transcription, nodule and lateral root initiation coverage an auxin maximum, cytokinin promotes auxin biosynthesis during nodule initiation
overall of N fixation?
key regulatory genes that control root nodule fomration identified
but
genes for rhizobial and plant immune response still obscure, how many genes will need to be engineered
how to control expression of genes needed for nodule formation?how to create microanerobic conditions needed for artificual nodule
