LAUSR

New insights about the role of nitric oxide (NO) metabolism during leaf senescence in Arabidopsis thaliana are presented. A gradual decrease in NO emission accompanied the dark-induced leaf senescence (DILS), and a transient wave of peroxynitrite (ONOO -) formation was detected by day 3 of DILS. The boosted ONOO - did not promote tryptophan (Trp) nitration, while the progress of senescence depleted the pool of 6-nitroTrp-containing proteins. Immunoprecipitation combined with mass spectrometry was used to identify 63 and 4 characteristic 6-nitroTrp-containing proteins in control and individually darkened leaves, respectively. The potential in vivo targets of Trp nitration were mainly related to protein biosynthesis and carbohydrate metabolism. In contrast, nitration of tyrosine-containing proteins was intensified two-fold on day 3 of DILS. Also, nitrative modification of RNA and DNA increased significantly on days 3 and 7 of DILS, respectively. Taken together, ONOO - can be considered as a novel pro-senescence regulator that fine-tunes the redox environment for selective bio-target nitration. Thus, DILS-triggered nitrative changes at RNA and protein levels promote developmental shifts during plant lifespan, and temporal adjustment in plant metabolism during adverse factors.