Question

Why do light-adapted plants have a higher level of glutamine than dark-adapted plants (and how is amino acid metabolism responsible for it)?

Answer 1

While glutamine is the primary nitrogen transport compound in most higher plants, asparagine also serves to transport nitrogen in several legumes and non legume species. Glutamine and asparagine serve different roles in nitrogen metabolism. Since glutamine is metabolically active and asparagine relatively inert, asparagine serves as a nitrogen storage compound in addition to transport). Thus, the ratio of glutamine asparagine transported in plants is affected by growth conditions. In light-grown plants, glutamine is the predominant nitrogen transport compound whereas in dark-grown or dark-adapted plants, asparagine levels predominate .The increased levels of asparagine in plants grown in the dark correlates with the fact that asparagine is a more economical compound with which to transport nitrogen (eg, has a higher N:C ratio than glutamine).

In pea, previously shown that while chloroplast GS2 gene expression is induced by light, the expression of the two pea AS genes (AS1 and AS2) are repressed by light.These results are in keeping with the physiological findings of glutamine and asparagine levels in these plant.More recently, it is shown that Arabidopsis has a single gene for glutamine dependent AS (ASI) which is also regulated by light in a negative fashion .

Thus glutamate variation occurs