Abstract
We have recently found in Arabidopsis thaliana a novel, oxidative stress-induced enzyme NADPH:2-alkenal α,β-hydrogenase (ALH) that catalyzes the α,β-hydrogenation of 2-alkenals, the lipid peroxide-derived endogenous toxins. We made ALH-overproducing transgenic tobaccos to verify the in vivo function of ALH. Three homozygous transgenic lines, whose leaves contained >20 times higher ALH activity than in the non-transgenics, showed higher tolerance against 4-hydroxynonenal (HNE), the major 2-alkenal, which inactivated PSII and caused necrosis, when administered to the leaves. The transgenics also showed higher tolerance against methylviologen (MV)-light treatment. The MV tolerance was solely attributable to the HNE detoxication by ALH, because the tolerances against HNE and against MV were correlated each other, while the levels of major known antioxidant enzymes, e.g. SOD, APX and catalase, in transgenic and control plants were the same. Thus, the lipid peroxide-derived 2-alkenals are injuring molecules in photooxidative stress. ALH protect cells by detoxifying them.
