Exhibits cGTPase activity; binds and hydrolyzes specifically GTP (PubMed:18801746). May participate in ribosome assembly and stability and thus regulates protein synthesis in chloroplasts. The GTPase activity requires MgCl(2)and the presence of either KCl or (NH(4))(2)SO(4). Involved in the post-transcriptional regulation of the methylerythritol phosphate (MEP) pathway. Involved in chlorophyll-a fluorescence regulation. May mediate the production or accumulation of nitric oxide (NO) which is a messenger molecule involved in hormonal signaling and defense responses in plant (PubMed:14526079, PubMed:16272429, PubMed:16690168 and PubMed:17351048). Acts as an antisenescence agent. Plays a crucial role in both extracellular calmodulin (ExtCaM)-triggered and salicylic acid (SA)-mediated H(2)O(2)-dependent stomatal closure. H(+) + 2 L-arginine + 3 NADPH + 4 O2 = 4 H2O + 2 L-citrulline + 3 NADP(+) + 2 nitric oxide Stimulated by calcium/calmodulin. Inhibited by L-NAME. Not activated by tetrahydrobiopterin (BH4), FAD, FMN, or heme. Was initially thought to be mitochondrial (PubMed:16272429). In fact seems to be chloroplastic (PubMed:18469163). Expressed in aleurone layer and the embryo. Constitutively expressed. Induced by abscisic acid (ABA) and lipopolysaccharides. Pale seedlings with a delayed development and greening of true leaves resulting in small plants with a characteristic virescent phenotype of pale young leaves but green mature leaves. Loss of NOS activity in mitochondria. Reduced extracellular calmodulin- (ExtCaM-) triggered and salicylic acid (SA)-mediated increase in NO levels and subsequent H(2)O(2)-dependent stomatal closure. Faster dark-induced senescence in leaves. Higher accumulation of hydrogen peroxide, superoxide anion, oxidized lipid, and oxidized protein. Increased hypersensitivity to salt stress and methyl viologen (MV) treatment. Enhanced accumulation of Na(+) but reduced accumulation of K(+) when exposed to NaCl leading to an enhanced sensitivity to salt. Post-transcriptional up-regulation of the methylerythritol phosphate (MEP) pathway. Enhanced resistance to fosmidomycin (FSM). Disturbed chlorophyll-a fluorescence induction in response to temperature variation, accompanied with altered polyamines accumulation. Belongs to the TRAFAC class YlqF/YawG GTPase family. NOA1 subfamily. Nitric oxide synthase (NOS) activity is dubious.