Studies on the Metabolism and Senescence of Nodulating and Nonnodulating Isolines of Soybean (Glycine Max L. Merrill Cv. Harosoy)

96 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1983.Field studies were conducted in 1981 and 1982 with the primary objective to determine if pod removal prevented senescence and affected nodulated and nonnodulated soybean plants similarly. A secondary objective was to compare physiological traits of nodulated and nonnodulated plants relative to productivity.Pod removal did not affect total plant dry weight or reduced-N accumulation, although reduced-N contents were lower in nonnodulated than nodulated plants. Pod removal did depress phosphorus accumulation by plants. Growth and storage of constituents by leaves and stems compensated for lack of pods, as evidenced by dry weight, reduced-N, phosphorus, and starch accumulation. Nutrient remobilization from leaves was prevented and leaf drop was greatly delayed by pod removal.Ribulose bisphosphate carboxylase (RuBP Case) activity (both years) and chlorophyll concentration (1981) was decreased in upper-canopy leaves by pod removal. In both years, RuBP carboxylase activity and chlorophyll concentration declined at the same time for all treatments, but rates of decline were less for depodded plants, which retained some RuBP carboxylase activity and chlorophyll at maturity. Non-nodulated plants had lower RuBP carboxylase activity (1982) and chlorophyll concentration (both years) than nodulated plants.Pod removal did not affect nitrate reductase profiles of upper-canopy leaves, as activities peaked soon after flowering and then rapidly declined to zero before maturity for all treatments. For the nodulated plants, acetylene reduction profiles were similar for podded and depodded plants, although loss of activity was slightly delayed for depodded plants.Less dry weight and N was partitioned to pods by nonnodulated than nodulated plants (both years) although dry weight accumulation was the same and starch accumulation greater for nonnodulated than nodulated plants. Thus, the moderate N stress of nonnodulated plants affected partitioning of photosynthate rather than net photosynthesis, which suggested a critical role for N in translocation of photosynthate to the grain.The results indicated that senescence was initiated at the same time for podded/depodded and nodulated/nonnodulated soybean plants. Also, remobilization of nutrients from vegetation did not appear to cause senescence, although it may have enhanced the rate of senescence. Since initiation of senescence appeared to be under genetic control, future work should perhaps focus on understanding and manipulating the course of senescence rather than the initial cause.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD