Variation of Nicotinamide Adenine Dinucleotide Phosphate Level in Bean Hypocotyls in Relation to O2 Concentration

Abstract

Slices of hypocotyls from 3-day-old seedlings of Vigna sesquipedalis in the germination stage were incubated under various gaseous conditions. The NADP + NADPH level in the hypocotyl slices changed with the oxygen tension. A high NADP+ NADPH level was observed under aerobic conditions and a low NADP+ NADPH level under anaerobic conditions. The 100xNADH/NAD+NADH ratio increased greatly under anaerobic conditions. In general a low NADP+NADPH level corresponded with a high lOOxNADH/NAD+NADH ratio. NADH was observed to be a very potent competitive inhibitor of NADP-formation from NAD. Accordingly, the slowness of NADH oxidation in hypocotyl tissue due to anaerobic conditions results in the inhibition of NADP formation. The variation of the NADP+NADPH level was observed to produce a modification of the carbohydrate metabolism. The NADP+NADPH level in Escherichia coli B(H) cells suspended in glucose solution also closely followed the change in the gaseous conditions.