Effect of salinity on phosphate accumulation and injury in soybean

Many soybean [Glycine max (L.) Merr.] genotypes that are grown in solution cultures are highly sensitive to the combination of both salinity and inorganic phosphate (Pi) in the substrate. This effect has been observed on numerous occasions on plants grown in a saline medium that contained a substantial amount of Ca (i.e., CaCl₂/NaCl=0.5 on a molar basis). Because Ca is important in regulating ion transport and membrane permeability, solution culture experiments were designed to examine the effects of various concentrations of Pi and ratios of CaCl₂/NaCl (0 to 0.5 on a molar basis) at a constant osmotic potential (−0.34 MPa) on this adverse interaction. Four soybean cultivars (‘Lee’, ‘Lee 74’ ‘Clark’ and ‘Clark 63’) were tested. No adverse salinity x Pi interaction was found on Lee at any ratio and leaf P and Cl were maintained below 300 and 200 mmol kg⁻¹ dry wt, respectively. Clark, Clark 63 and Lee 74 soybean plants, on the other hand, were severely injured by solution salinity (−0.34 MPa osmotic potential) when substrate Pi was ≥0.12 mM. Reduced substrate Ca did not intensify the salinity x Pi interaction. On the contrary, the onset of injury was hastened and more severe with increased CaCl₂/NaCl ratios in isotonic solutions. Shoot and root growth rates decreased as injury increased. Leaf P concentrations from these cultivars grown in saline solutions with 0.12 mM Pi were excessive (>600 mmol kg⁻¹ dry wt) compared with concentrations commonly found in soybean leaf tissue yet they were independent of the severity of injury. Since leaf Cl increased wiht increased CaCl₂/NaCl ratio, we suspect that the severity of foliar injury was related to the combined effects of excessive P and Cl within the tissue. Lee 74, the only injured cultivar examined that excluded Cl from its leaves, was less sensitive than either Clark cultivar and its injury was characteristically different. Other ion interactions were reported that may have played a role in injury susceptibility.     

Nitrogen fixation (15N dilution) with soybeans under Thai field conditions

Controlled environment and field studies were conducted to determine relationships between various measurements of N₂ fixation using soybeans and to use these measures to evaluate a number ofBradyrhizobium japonicum strains for effectiveness in N₂ fixation in Thai soils.¹⁵N dilution measurements of N₂ fixation showed levels of fixation ranging from 32 to 161 kg N ha⁻¹ depending on bacterial strain, host cultivar and location. Midseason measures of N₂ fixation were correlated with each other, but not related measures taken at maturity. Ranking ofB. japonicum strains based on performance under controlled conditions in N-free media were highly correlated with rankings based on soybean seed yields and N₂ fixation under field conditions. This study showed that inoculation of soybeans with effectiveB. japonicum strains can result in significant increases in yield and uptake of N through fixation. The most effective strains tested for use in Thai conditions were those isolated from Thai soils; however, effective strains from other locations were also of benefit.     

热刺激在植物体内的传递效应

以高粱(Sorghum bicolor)和大豆(U.S.Soybean)幼苗为材料研究了仅植物很部受到热刺激时,其未直接受到温度影响的叶组织细胞的反应。当13天龄的高粱幼苗根部经受45℃4小时热处理时,发现其未直接受到热刺激的叶细胞内合成了一些异常的蛋白质,估测的分子量分别为80kD、70kD、33kD和17kD。最明显的两条蛋白质谱带是70kD和17kD。6天龄的大豆幼苗,当其根部经受40℃3小时热处理时,在其叶细胞内也检测到两条较为明显的蛋白质谱带,其分子量分别为60kD和17kD。观测到的这些异常蛋白质命名为‘热应激效应蛋白’,并与热应激蛋白在分子量大小分布上进行了比较。另外,还报道了利用蛋白质合成抑制剂,亚胺环己酮(cyclohexlmide)探讨了热应激蛋白与植物热耐性方面的可能关联。     

N2 fixation by soybean-Bradyrhizobium combinations under acidity,low P and high Al stresses

Five strains of Bradyrhizobium japonicum (USDA 6, 110, 122, 138, and 143) were screened in cell culture for tolerance to acidity (pH 4.2, 4.4, and 4.6) and Al (0, 3, 4, 5, and 6 mg L^–1) under low P conditions. Each strain was later grown in association with seven soybean [Glycine max. (L) Merr.] cultivars which were also screened for tolerance to the same stresses in nutrient culture to determine which soybean-Bradyrhizobium combinations would establish the most effective symbiotic N₂ fixing relationships. Results indicated that strains USDA 110 and 6 were more tolerant than USDA 122, 138 and 143 with USDA 110 being the most tolerant. Acidity appeared to be the more severe stress; but even when strains showed tolerance to the stresses, cell numbers were significantly reduced. This suggests that colonization of soils and soybean roots can be adversely affected under similar conditions in the field which may result in reduced nodulation. The strains found to be more tolerant to the stresses were more effective N₂ fixers in symbiosis with all soybean cultivars, with USDA 110 being definitely superior. The association between the more tolerant strains and cultivars had the largest nitrogenase activity. Further studies on the inclusion of tolerant Bradyrhizobium strains in inoculum used on tolerant soybean cultivars in the field are warranted.     

Formation of nodules on non-nodulating soybean T201 after treatment with 2,4-dichlorophenoxyacetate

The formation of effective root nodules on a non-nodulating line (T201) of soybean (Glycine max (L.) Merr.,) was induced by a treatment with 2,4-dichlorophenoxyacetate (2,4-D). The induced nodules, inoculated with mixed Bradyrhizobium japonicum strains A1017 and IRj2101, had a normal internal structure, red in colour and the cells being filled with bacteroids. Externally, the induced nodules were of unusual shape, being paired or gourd-like in form and were attached to thickened roots. The nodules were capable of acetylene reduction (3.1–3.5 moles g^-1 fresh weight nodules h^-1), allowing the growth of plants with dark green leaves.     

Native root-nodule bacteria of traditional soybean-growing areas of northern Thailand

Over 1500 root-nodule bacteria were isolated from a range of uninoculated soybeans, and one cowpea, trap-hosts, sown in 1985 into traditional soybean-growing areas of soybean-growing areas of northern Thailand. Most isolates were slow-growing Bradyrhizobium japonicum. Using a modified bottle-jar technique, 586 of the isolates were tested with a range of soybean hosts and one cowpea host. The results indicated:

Pea lectin is correctly processed,stable and active in leaves of transgenic potato plants

A gene encoding the preproprotein of the pea (Pisum sativum) lectin was expressed in transgenic potato plants using a cauliflower mosaic virus (CaMV) 35S promoter or a tobacco ribulose bisphosphate carboxylase small subunit (ssRubisco) promoter. Presence of the pea lectin to levels greater than 1% of total soluble leaf protein was detected by radioimmunoassay (RIA). The pattern of expression derived from the two promoters was established using both RIA and a squash-blot immunolocalisation technique. Western blotting demonstrated that the preproprotein was correctly processed, generating and subunits that assembled to give an isolectin form observed in pea seeds and roots. It was also found that the haemagglutination activity and specificity of pea lectin synthesised in transgenic potato leaves was comparable to purified lectin from pea cotyledons.     

Phenotypically normal transgenic T-cyt tobacco plants as a model for the investigation of plant gene expression in response to phytohormonal stress

The tumour-inducing T-DNA gene 4 (T-cyt gene) of the nopaline Ti plasmid pTiC58 was cloned and introduced into tobacco cells by leaf disc transformation using Agrobacterium plasmid vectors. Tobacco shoots exposed to elevated cytokinin levels were unable to develop roots and lacked apical dominance. Using exogenously applied phytohormone manipulations we were able to regenerate morphologically normal transgenic tobacco plants which differed in endogenous cytokinin levels from normal untransformed plants. Although T-cyt gene mRNA levels, as revealed by dot-blot hybridization data, in these rooting plants were only about half those in primary transformed shoots the total amount of cytokinins was much lower than in crown gall tissue or cytokinin-type transformed shoots as reported by others. Nevertheless the cytokinin content in T-cyt plants was about 3 times greater than in control tobacco plants.Elevated cytokinin levels have been shown to change the expression of several plant genes, including some nuclear genes encoding chloroplast proteins. Our results show that the mRNA levels of chloroplast rbcL gene increase in cytokinin-type transgenic tobacco plants as compared with untransformed plants. Data obtained suggest that T-cyt transgenic plants are a good model for studying plant gene activity in different parts of the plant under endogenous cytokinin stress.     

Differential inactivation and methylation of a transgene in plants by two suppressor loci containing homologous sequences

In a previous study on doubly transformed tobacco plants, we observed the unexpected inactivation in trans of T-DNA-I (encoding Kan^rNOS) following the introduction into the same genome of an unlinked copy of T-DNA-II (encoding Hyg^rOCS). This inactivation, which probably resulted from interactions between homologous regions on each T-DNA, was correlated with methylation in the nos _pro, which controlled the expression of both the nptII and nos genes. In this paper, we show that the inactivation and methylation of the nos _pro nptII gene in the presence of a suppressor T-DNA-II locus can be either complete (epistasis) or partial (cellular mosaicism). In plants showing partial suppression, the strength of the Kan^r phenotype, which apparently reflected the proportion of cells expressing the nptII gene, was inversely correlated with the degree of methylation of the nos _pro. The extent of nos _pro methylation decreased progressively in successive generations as suppressor T-DNA-II loci were crossed out. The strength of the Kan^r phenotype was improved and nos _pro methylation was less extensive in first generation Kan^r progeny obtained from outcrossing with untransformed tobacco than from self-fertilization.     

Biological control of Pythium damping‐off by seed‐treatment with pseudomonas putida: Relationship with ethanol production by pea and soybean seeds

The relationship between biocontrol activity of Pseudomonas putida strain N1R against Pythium ultimum on pea and soybean seeds and the reduction in ethanol evolution by imbibed seeds was investigated under different treatment conditions, including temperature and numbers of seed‐applied cells of the bacterium. Treatment with strain N1R increased emergence at all temperatures, except for soybean at 12 °C and reduced ethanol concentration in the spermosphere of imbibed seeds at several temperatures. The concentration of bacterial cells in the seed treatment suspension also significantly affected biocontrol efficiency and reduced ethanol production, especially in pea seeds. In contrast, the duration (0–7 h) of submergence of seeds in bacterial suspension had little effect on biocontrol activity of N1R, although submergence of soybean seeds reduced their emergence even in the absence of the pathogen or biocontrol agent. Competition for seed‐derived compounds, including ethanol, is suggested to be one possible mechanism of biocontrol of Pythium by strain N1R, which is not known to produce antifungal antibiotics.