STUDIES ON A NONFIXING MUTANT OF PEA (PISUM-SATIVUM L) .1. PHENOTYPICAL DESCRIPTION AND BACTEROID ACTIVITY

In this study a supernodulating non-fixing (AR-) pea mutant FN1 was compared with the supernodulating parent type nod3. Phenotypically the fix- mutant differed from the parent type nod3 by having severe nitrogen deficiency symptoms and an increased nodule mass per plant in N-free hydroculture. The non-fixing character was monogenic and recessive, while grafting experiments showed that the expression was dependent on the genotype of the stock, presumably the roots. The mutated gene was designated nof1. The release of bacteroids from the infection threads into the cortex cells looked normal when viewed under the light microscope. A large accumulation of starch granules in the proximal cortex cells of the mutant indicated that there was an underconsumption of energy in the nodules. Electron microscopy studies indicated an early senescence of the bacteroids and the surrounding peribacteroid membranes. In contrast with bacteroids from the parent type nod3, bacteroids isolated from FN1 nodules were not able to reduce acetylene under micro-aerobic conditions. Bacteroids from both the fix- mutant and the parent type nod3 were able to take up succinate in vitro. © 1990.