SUMMARY: Trifolium subterraneum plants grown at 30°C root temperature nodulated 3 days after inoculation with Rhizobium trifolii and nitrogenase activity (determined by acetylene-reduction) was detected 3 days later. While all four strains of R. trifolii examined formed effective nodules at 22°C, at 30°C only the nodules formed by strain TAI showed a rapid increase in nitrogenase activity. Light and electron microscopy of the nodules formed by one temperature-sensitive strain (NA30) showed the following abnormalities: multiple branching and distortion of the infection threads; failure of many bacteria to develop into characteristic bacteroids; continued division of these bacteria to give atypical multiple occupancy of the membrane envelopes; release of polysaccharide from ruptured infection threads into the host cytoplasm; rapid degeneration of the membrane envelopes and their contents. While the development of the membrane envelopes appeared to be under host control, the effect of the higher temperature on bacteroid development was highly strain specific.
Upon transfer of nodulated plants from 22 to 30°C, bacteroid tissue in nodules formed by the temperature-sensitive strain NA30 broke down rapidly but nodules formed by strain TAI were less severely affected.
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