Improving Nitrogen Use Efficiency

Question 1

What are the two biological ways ammonia is generated

Answer 1

• Reduction of nitrate (predominant form of soil N) to ammonia
• Reduction of N2 by micro-organisms, often in symbiotic association with plants

Question 1

Why is nitrogen important for plants?

Answer 1

• Needed for amino acids, proteins and other cellular constituents
• Generally the most limiting nutrient to plant growth
• Deficiency results in stunted growth and chlorotic leaves

Question 2

What are the key characteristics of the Haber Bosch process?

Answer 2

• Requires high temp (300-600 degrees c)
• Requires high pressures (20-80 MPa)
• Low yield
• Uses 1-2% of global energy
• 85% of ammonia produced goes to make fertiliser

Question 3

What are the characteristics of nitrogen-fixing microorganisms?

Answer 3

• Over 250 species (bacteria and cyanobacteria) can fix nitrogen
• Use the nitrogenase enzyme
• Can be free-living in soil or associated with plants (normally legumes)

Question 4

What are the three major issues with nitrogen fixation?

Answer 4

• Reaction is very sensitive to oxygen
• Requires large input of energy (ATP and reductant)
• Side reaction - reduction of 2H+ to H2

Question 5

How is carbon distributed in legume nodules?

Answer 5

For every 100 carbon atoms fixed in leaves:
- 5 C for growth and maintenance
- 12 C for production of ATP and NADH to fix N
- 15C to provide carbon for NH3 assimilation

Question 6

What are the steps in root nodule formation?

Answer 6

• Root hair forms infection thread by plasma membrane invagination
• Rhizobium bacteria penetrate infection thread, forming bacteroid within vesicels
• Root cells grow around bacteroid, forming nodule
• Nodule develops vascular tissue for material exchange

Question 7

What signals are involved in nodule formation?

Answer 7

• NOD factors emitted from bacterium
• Plant receptors recognise these factors
• Plant emtis signals (flavonoids)
• Host cell recognises healthy bacterium

Question 8

What are the key challenges in engineering nitrogen fixation into non-legumes?

Answer 8

• Genes for rhizobial infection and plant immune response still unclear
• Control of gene expression for nodule formation
• Creating microaerobic conditions in artifical nodules
• Understanding how many genes need to be engineered

Question 9

What is the nitroplast?

Answer 9

• Novel organelle found in some algae
• Result of symbiosis where bacteria-derived organelle provides N to algae
• Algae provides C to the organelle

Question 10

What does next-generation sequencing enable in comparative genomics and crop engineering?

Answer 10

• Large scale analysis to trace phenotypic trait changes and identify key genes like transcription
• Can identify genetic components underlying phenotypic traits for targeted modifications

Question 11

What developmental processes share evolutionary conservation?

Answer 11

Nodule formation and lateral root development

Question 12

What role does the pericycle play in root development?

Answer 12

It generates new lateral roots for environmental exploration and plant anchorage
Pericycle activation is responsive to environmental cues

Question 13

What regulates lateral root formation?

Answer 13

Auxin maxima driven by PIN-mediated auxin transport

Question 14

What are PIN proteins#?

Answer 14

Auxin transporters crucial for establishing auxin gradients

Question 15

What is a shared feature of lateral root and nodule development?

Answer 15

Convergence at an auxin maximum and overlapping transcriptional programs

Question 16

How does cytokinin influence nodule initiation?

Answer 16

Promotes auxin biosynthesis to facilitate organ development