Electro donation from ascorbic acid on nitrite assimilation in spinach (Spinacia oleracea L.) leaves under dark conditions

For verification that ascorbic acid can affect on the process of nitrite reduction, reduced form of ascorbic acid (AsA) dissolved in the pH 7.5 buffer solution was added and vacuum-infiltrated into spinach (Spinacia oleracea L.) leaf sections. The endogenous nitrite was reduced in accordance with AsA oxidation by the higher rate with addition of AsA than that without it. In addition, when N-15-labelled nitrite was added to the leaf sections together with AsA, higher N-15 contents were found in ammonia and the reduced soluble form of N (ammonia and amino acids) within short periods in the leaf sections treated with AsA than without it. The crude enzymes in the leaf extract from spinach leaves could reduce nitrate to nitrite in the presence of AsA but the rate was less than that in the presence of NADH. Formation of nitric oxide from nitrite by nitrate reductase in leaf extract in the presence of AsA (at pH 7.5) was estimated to be insignificant. Addition of AsA and (Fd) ferredoxin to the leaf extract could reduce nitrite at higher rate than that of NADPH(Nicotinamide Adenine Dinucleotide Phospate)-FNR(Ferredoxin NADP(+) Reductase) -Fd system. These results suggest the possible electron donation from AsA to nitrite reduction via Fd in the dark.