Nitrogen

Question 1

Which forms of nitrate are available to non-leguminous plants?

Answer 1

Reduced forms such as nitrate and ammonium

Question 2

What can the plant do with nitrate once it has been taken up?

Answer 2

Store it in the vacuole, transported from the root to the shoot or assimilated into amino acids.

Question 3

When is the low-affinity nitrate transport system used?

Answer 3

When the external nitrate is high - lower than 50um.

Question 4

When is the high-affinity nitrate transport system used?

Answer 4

When the external nitrate is low - Lower than 5mM.

Question 5

What happens in the roots and shoots to assimilate nitrate?

Answer 5

Reduced to nitrite by the enzyme nitrate reductase and then translocated from the cytosol to the plastids where it is reduced to ammonia by nitrite reductase.

Question 6

Name 2 nitrate transporters

Answer 6

NRT1 and NRT2

Question 7

What regulates NRT2?

Answer 7

Nitrogen Starvation - high-affinity nitrate transporters

Question 8

What regulates NRT1?

Answer 8

An abundance of nitrogen - low-affinity nitrate transporters with the exception of AtNRT1.1 which is a dual affinity transporter.

Question 9

What allows a switch between high and low-affinity receptors?

Answer 9

Phosphorylation by kinases such as CIPK23.

Phosphorylation of a HAT alters the binding properties so it is no longer monomeric and becomes a LAT.

Question 10

which enzymes assimilate ammonia?

Answer 10

Glutamine synthetase and glutamate synthetase

Question 11

What does GOGAT do?

Answer 11

Recycles glutamate and incorporates 2-oxoglutarate carbon skeletons for transfer of amino groups.

Question 12

What is the major route of 2-OG production?

Answer 12

Isocitrate dehydrogenase in the mitochondria (mostly) or in the cytosol.

Question 13

What does oxaloacetate do?

Answer 13

Inputs acids into the TCA cycle for the formation of 2-OG.

Question 14

What are lateral roots for?

Answer 14

Proliferating into nitrate rich patches in the soil.

Question 15

What do lateral roots develop from and where are they found?

Answer 15

The pericycle, found in the primary root.

Question 16

How does auxin regulate the spacing of lateral root growth?

Answer 16

Activating the expression of plethora (PLT) genes and the production of cytokinin (CK) in the lateral root primordia.

Question 17

Is lateral root growth systemic or constitutive?

Answer 17

Systemic

Question 18

Is inhibition of lateral root growth systemic or constitutive?

Answer 18

Constitutive

Question 19

How does glutamate effect LR development?

Answer 19

Inhibitory effect on primary roots and a stimulatory effect on LRs. Shorter, more branched root system.

Question 20

How does ABA effect LR development?

Answer 20

Inhibits lateral root growth in stressful conditions such as drought.

Question 21

Is abi4-1 an ABA signalling mutant or a synthesis mutant?

Answer 21

Signalling

Question 22

Is abi1-1 an ABA signalling mutant or a synthesis mutant?

Answer 22

Synthesis

Question 23

What does ammonia do in the GS-GOGAT cycle?

Answer 23

Converts an amino acid with 1N to an amino acid with 2N (glutamate to glutamine)

Question 24

How are two molecules of glutamate achieved in the GS-GOGAT cycle?

Answer 24

Another enzyme transfers one of the amino acids onto 2-OG (the carbon skeleton)

Question 25

what does aminotransferase do?

Answer 25

Shuffles the amino groups around

Question 26

What can 13 of the amino acids be synthesised from?

Answer 26

Glu, Asp and Ala.

Question 27

Which pathway does Glyphosate (a widely used herbicide) take advantage of?

Answer 27

Shikimate

Question 28

What does glyphosate do?

Answer 28

Prevents synthesis of tyrosine, tryptophan and phenylalanine

Question 29

What is the most abundant form of auxin?

Answer 29

Indoleacetic acid

Question 30

How is tryptophan converted into indoleacetic acid?

Answer 30

• Converted to IPA by Trp transaminase
• Converted to IAld by IPA decarboxylase
• Converted to IAA by IAld dehydrogenase

Question 31

Large numbers of transcripts of what were increased in abundance in leaves suffering from nitrogen deficiency?

Answer 31

Protein kinases and protein phosphatases

Question 32

What is the ubiquitin-proteasome pathway?

Answer 32

Causes protein degradation as a mechanism of adaption to low nitrogen conditions.

Question 33

What gene expression changes are caused by low nitrogen?

Answer 33

1. Primary nitrogen assimilation genes are decreased
2. Amino acid degredation genes are increased
3. Starch accumulation genes are increased.
4. Genes for secondary metabolism are increased
5. Senescence genes are increased

Question 34

What is nitrogen use efficiency?

Answer 34

Product of nitrogen uptake efficiency and nitrogen utilisation efficiency.

Question 35

What is nitrogen uptake efficiency?

Answer 35

The ability to take up and store nitrogen from the soil as metabolites and proteins

Question 36

What is the nitrogen harvest index?

Answer 36

The portion of nitrogen from initial uptake which is then transferred into harvested organs.

Question 37

What is senesence for?

Answer 37

Allow plants to improve nutrient economy and survive nutriet starvation

Question 38

What is RuBisCo proteolysis initiated by?

Answer 38

Oxidation of protein cysteine residues.

Question 39

What are stromules?

Answer 39

Membranous tubes that increase the plastic surface area, they are highly dynamic and allow the tranfer of molecules between chloroplasts. RuBisCo containing bodies are though to bud off the end of stromules.