Possible electron donation from ascorbic acid to nitrite reduction in the plant leaf

摘要

Nitrate in the plant leaf cells is reduced to nitrite at the cytoplasm by nitrate reductase (NR) and the nitrite is reduced to ammonia at the chloroplast by nitrite reductase (NiR). Much of ascorbic acid exists as reduced form(AsA) in the cytoplasm and chloroplast at high concentrations. We examined the effect of As A on nitrate reduction process. When As A was added to spinach (Spinacia oleracea L.) leaf sections, reduction of endogenous nitrite was accelerated during the short time. In addition, when 15N-labelled nitrite was exogenously added to the leaf section, ~(15)N was incorporated to ammonia and amino acids more by AsA addition. Reduction of nitrate in the leaf extract with addition of AsA was significantly increased but less than that withNADH. Rate of nitrite reduction in the leaf extract under darkness was higher with addition of AsA plus Fd than with NADPH plus FNR plus Fd. By the re-constituted system with AsA, Fd and NiR, nitrite was reduced to ammonia and more so by addition of leafextract. These results demonstrate that AsA can affect the process of nitrate reduction, especially nitrite reduction in the darkness. AsA can donate electrons to Fd directly, and plant factors (PFs) derived from the leaf extract can stimulate the reduction of nitrite.