Effect of exogenous ribonucleic acid and some of its nitrogen bases on nitrate reduction in plant tissues and on the symbiotic fixation of atmospheric nitrogen in the soybean
Ratner, E.I.; Samoilova, S.A.
Fiziol Rast 13(6): 1041-1053
Adenine and especially uracil exert a positive effect on nitrate reduction in sunflower roots and on the activity of the enzyme nitrate reductase in sunflower tissues. The protein content considerably rises in sunflower plants fed with RNA or its decomposition products. A correlated increase of the total amount of nitrogen was correspondingly observed (the root absorbing power and nitrate reduction increased) ; no increase was observed in the RNA and DNA content which in some cases may even decrease. A positive effect of uracil and to a smaller extent of adenine and RNA on the symbiotic nitrogen fixation rate is observed in soybean. Enhancement of the nitrogen fixation rate is closely related to the effect of adenine and uracil on the nitrate reductase activity in leaves as well as in the soybean nodules. The nitrate reductase activity in tubercles during the period of most intensive nitrogen fixation (early phases of fruit formation) is hundreds of times greater than in the leaves. The results obtained are in accordance with previous data from experiments with vitamins of the vitamin B group and indicate the possibility of an oxidative path in the primary reactions of symbiotic fixation of free nitrogen and also the significance of nitrate reductase in the nitrogen fixation process itself.