Nitric oxide and light co-regulate glycine betaine homeostasis in sunflower seedling cotyledons by modulating betaine aldehyde dehydrogenase transcript levels and activity.

Glycine betaine (GB), an osmolyte, is produced in chloroplasts by the action of betaine aldehyde dehydrogenase (BADH) on its precursor betaine aldehyde. The present work highlights the significance of nitric oxide (NO) in GB homeostasis as a long-distance salt (120 mM NaCl) stress-elicited response. In light-grown seedling cotyledons, both the activity and transcript levels of BADH are much higher than in dark-grown seedlings irrespective of salt stress. Significantly high accumulation of GB in dark-grown seedling cotyledons indicates its preferential mobilization from cotyledons to other plant parts in light-grown seedlings. NO donor application (diethylenetriamine) maintains high BADH activity in light, although in dark it is brought down marginally. BADH levels are maintained high in light than in dark in respective treatments. Reversal of the effect of NO donor on age-dependent GB content, BADH activity, and transcript levels by NO scavenger (diethyldithiocarbamate) further demonstrates the impact of NO on GB homeostasis in light- and dark-grown seedlings in an age-dependent manner, major modulation being observed in 4-d-old seedlings. The present work, thus, provides new information on co-regulation of GB homeostasis by NO and light. It also puts forward new information of GB-NO crosstalk in maneuvering salt stress sensing as a long-distance response in seedlings.