Changes in pyridine nucleotide levels in leaves and roots of bean plants (Phaseolus vulgaris L.) during phosphate deficiency

A large decrease in inorganic phosphate content in bean plants (Phaseolus vulgaris L. cv. Zlota Saxa) grown on phosphate deficient medium induced the changes in the levels of pyridine nucleotides. The decrease in the level of NADP(+) was noted only in roots. However, NAD(+) content decreased both in leaves and roots. In -P leaves and roots the concentration of NADPH increased, but the content of NADH did not change. More pronounced changes in the levels of pyridine nucleotides in roots as compared with leaves might be a result of the effect of Pi-deficiency on the overall rate of respiration. Modifications in the respective nucleotide levels were reflected by higher values of the NADPH/NADP(+), NADH/NAD(+) and RC ratios both in leaves and roots. Relative accumulation of reduced forms of pyridine nucleotides in 18-day-old -P bean plants indicates that the equilibrium of oxidation-reduction reactions was shifted in the direction of redox equivalents-yielding system both in leaves and roots. Cytosolic NAD(+)-dependent malate dehydrogenase and NADP(+)-malic enzyme activities showed changes dependent on the level of particular forms of pyridine nucleotides. The changes in the levels of particular forms of pyridine nucleotides after 14 days of plant growth without Pi in the nutrient medium appear to be a delayed plant response to phosphate deficit stress.