Soybean response to nodulation by bradyrhizobia differing in rhizobitoxine phenotype

Abstract

Rhizobitoxine-producing (RT +) strains of Bradyrhizobium japonicum, differing in their abilities to induce foliar chlorosis with 'Forrest' soybean (Glycine max [L.] Merr.), were evaluated for effects on short term shoot productivity, nodulation, N 2 fixation, and nodule protein production under greenhouse conditions. Soybeans were singly inoculated with washed suspensions of (Group II) USDA strains 31, 46, 76, 94, 110, 123 or 130. Strains USDA 110 and USDA 123 (Group I/Ia) were included as RT-controls. The plants were cultured in the absence of combined N in horticultural-grade vermiculite for 49 days. Beginning 21 days after planting, plants were evaluated weekly for chlorophyll, leaf protein and biomass accumulation, nodular contents of leghemoglobin, soluble protein and RT, and total shoot N content. Rhizobitoxine was detected in nodules of all RT + strains with the exception of USDA 31. However, only USDA 76 and USDA 94 produced both quantifiable concentrations of RT and symptoms of RT-induced chlorosis. Coincident with moderate to severe chlorosis were reductions in chlorophyll concentrations, shoot and nodule dry weight, leaf protein and total N 2 fixation. During extended periods of severe chlorosis, reductions in Lb and soluble nodular protein were observed. Based on carbon accumulation, all non-chlorotic treatments were statistically more productive than the chlorotic treatments. Similarly, non-chlorotic Group II treatments tended to fix less carbon relative to the RT-Group I/Ia controls, although these differences were not statistically significant. The results of this study suggest that, in the absence of discernable foliar chlorosis, the effect of RT + (Group II) nodulation on short term soybean productivity is minimal.

Soybean response to nodulation by rhizobitoxine-producing bradyrhizobia as influenced by nitrate application

“…Previous short-term studies conducted under greenhouse conditions have shown that severe RT-induced chlorosis is accompanied by reductions in shoot dry weight, leaf surface area, leaf chlorophyll concentration and soluble leaf protein content (Teaney and Fuhrmann, 1992). In the present study, application of 7.5 mM KNO 3 significantly alleviated all of these symptoms.…”

“…Separation of the bacteroids from the nodule cytosol was achieved by a homogenization-centrifugation procedure (Pfeiffer et al, 1983;Teaney and Fuhrmann, 1992). Separation of the bacteroids from the nodule cytosol was achieved by a homogenization-centrifugation procedure (Pfeiffer et al, 1983;Teaney and Fuhrmann, 1992).…”

“…Separation of the bacteroids from the nodule cytosol was achieved by a homogenization-centrifugation procedure (Pfeiffer et al, 1983;Teaney and Fuhrmann, 1992). Leghemoglobin (Lb) content in the cytosol was determined using a pyridine hemochrome assay (Bergersen et al, 1973;Teaney and Fuhrmann, 1992). Leghemoglobin (Lb) content in the cytosol was determined using a pyridine hemochrome assay (Bergersen et al, 1973;Teaney and Fuhrmann, 1992).…”

“…Rhizobitoxine content was estimated as described by Teaney and Fuhrmann (1992). Briefly, nodule cytosol was partially purified by ion exchange chromatography.…”

Comparison of rhizobitoxine-induced inhibition of ?-cystathionase from different bradyrhizobia and soybean genotypes

“…The RT sensitivity of bradyrhizobia/3-cystathionase differed among the strains examined, and values Of VRr ranged from -0.34 to -0.67% activity min -l #M -l RT. The strain yielding the most sensitive/3-cystathionase was USDA 94 which also has been shown to produce the greatest amount of RT among the strains investigated both in culture and as a nodule symbiont (Teaney and Fuhrmann, 1992). /3-cystathionase obtained from bradyrhizobia, soybean, E. coli, and spinach exhibited different inhibition kinetics (Figure 3).…”