Light modulates activity and expression of glutamine synthetase isoforms in maize seedling roots

Abstract

In maize roots, continuous illumination inhibits chloroplastic glutamine synthetase (GS2) activity, which decreased in light from 72.8% in 4-day-old to 26% in 10-day-old plants. In dark-adapted plants transferred to light for 6 days, GS2 activity declined from 100% to 41%, but in light-adapted plants transferred to darkness, it increased to the level of the dark control. Changes of cytosolic (GS1) activity were minor, with a similar trend. Quantitative RT-PCR revealed that light/dark treatments moderately affected only transcription of GS1 isoforms, with the exception of GS1-2, which was dramatically induced by darkness and repressed by light.