Introduction, development, and characterization of supernodulating soybean mutant - nitrate inhibition of nodulation and nitrogen fixation in supernodulating soybean mutant

摘要

Inhibition of nodule formation and nitrogen fixation by soil nitrogen, primarily nitrate, is well known in legume plants. The present study was undertaken to evaluate the effect of NO3- on the nodulation, nitrogenase activity and growth of supernodulating soyabean mutant and its wild type. A greenhouse study was conducted to compare two supernodulating mutants, SS2-2 and nts382, with the normal nodulating cultivar Sinpaldalkong 2 when grown in a 1-l styroform cup filled with sand and fertilized with five levels of NO3- (0, 2, 4, 8 and 12 mM). During the growth period, each plant was supplied two or three times a week with 50 mL of nutrient solution. Supernodulating soyabean mutants, SS2-2 and nts382, showed more nodules and nodule mass, and greater C2H2 activity than the wild type, Sinpaldalkong 2, regardless of the level of exogenous nitrogen supply. On the other hand, total dry weight of the SS2-2 mutant, which was smaller than Sinpaldalkong 2, did not respond to the various NO3--N levels. Thissuggested that SS2-2 could maintain fairly high total dry weight at the low NO3--N level, even in the absence of exogenous NO3--N in the nutrient solution. From the reduced top growth and high nitrogen fixing ability of supernodulating mutants, it was surmised that supernodulating mutants could potentially protect agricultural environments from pollution through a reduction in nitrogen fertilization as well as maintain fairly high yield with increasing planting density.