The Effect of Short-Term H_2S Fumigation on Nitrate Reductase Activity in Spinach Leaves

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Short-term exposure of spinach plants to 250 ppb H_2S at a photon fluence rate of 35 μmol m^<-2> s^<-1> (within the 400-700 nm range) in the ambient air did not affect in vitro nitrate reductase activity (NRA) in the leaves. Likewise, H_2S exposure did not significantly affect in vivo NRA measured under anaerobic conditions. In vivo NRA of untreated plants was apparently inhibited in the presence of oxygen. However, short-term H_2S exposure increased in vivo "aerobic" NRA up to five fold of that of untreated plants. H_2S induced increase of in vivo "aerobic" NRA depended on the sulfide concentration. After 24 hours of exposure maximal increase (two to five fold) of in vivo NRA "aerobic" was observed at 220 ppb H_2S. It is proposed that H_2S inhibited NADH oxidizing enzymes, which resulted in an increase in NADH supply to nitrate reductase (NR) in the presence of oxygen. It was unlikely that the increase in in vivo "aerobic" NRA in sulfide exposed plants was due to an altered competition between mitochondrial respiration and NR since leaf respiration was not affected by an exposure to 250 ppb H_2S.
日本植物生理学会の論文