Abstract
A split-root growth system was employed to evaluate the effect of NaCl on nodule formation by soybean (Glycine max L. Merr. cv Davis). By applying the salinity stress and rhizobial inoculum to only one-half the root system, the effects of salinity on shoot growth were eliminated in the nodulation process. Rhizobium colonization of inoculated root surfaces was not affected by the salt treatments (0.0, 26.6, 53.2, and 79.9 millimolar NaCl). While shoot dry weight remained unaffected by the treatments, total shoot N declined from 1.26 grams N per pot at 0.0 millimolar NaCl to 0.44 grams N per pot at 79.9 millimolar NaCl. The concentration of N in the shoot decreased from 3.75% N (0.0 millimolar NaCl) to 1.26% N at 79.9 millimolar NaCl. The decrease in shoot N was attributed to a sharp reduction in nodule number and dry weight. Nodule number and weight were reduced by approximately 50% at 26.6 millimolar NaCl, and by more than 90% at 53.2 and 79.9 millimolar NaCl. Nodule development, as evidenced by the average weight of a nodule, was not as greatly affected by salt as was nodule number. Total nitrogenase activity (C2H2 reduction) decreased proportionally in relation to nodule number and dry weight. Specific nitrogenase activity, however, was less affected by salinity and was not depressed significantly until 79.9 millimolar NaCl. In a second experiment, isolates of Rhizobium japonicum from nodules formed at 79.9 millimolar NaCl did not increase nodulation of roots under salt stress compared to nodule isolates from normal media (0.0 millimolar NaCl). Salt was applied (53.2 millimolar NaCl) to half root systems at 0, 4, 12, and 96 hours from inoculation in a third experiment. By delaying the application of salt for 12 hours, an increase in nodule number, nodule weight, and shoot N was observed. Nodule formation in the 12- and 96-hour treatments was, however, lower than the control. The early steps in nodule initiation are, therefore, extremely sensitive to even low concentrations of NaCl. The sensitivity is not related to rhizobial survival and is probably due to the salt sensitivity of root infection sites.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Bohlool B. B., Schmidt E. L. Nonspecific staining: its control in immunofluorescence examination of soil. Science. 1968 Nov 29;162(3857):1012–1014. doi: 10.1126/science.162.3857.1012. [DOI] [PubMed] [Google Scholar]
- Broughton W. J., Dilworth M. J. Control of leghaemoglobin synthesis in snake beans. Biochem J. 1971 Dec;125(4):1075–1080. doi: 10.1042/bj1251075. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kirkham M. B., Gardner W. R., Gerloff G. C. Leaf water potential of differentially salinized plants. Plant Physiol. 1969 Oct;44(10):1378–1382. doi: 10.1104/pp.44.10.1378. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kosslak R. M., Bohlool B. B., Dowdle S., Sadowsky M. J. Competition of Rhizobium japonicum Strains in Early Stages of Soybean Nodulation. Appl Environ Microbiol. 1983 Oct;46(4):870–873. doi: 10.1128/aem.46.4.870-873.1983. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Schmidt E. L., Bakole R. O., Bohlool B. B. Fluorescent-antibody approach to study of rhizobia in soil. J Bacteriol. 1968 Jun;95(6):1987–1992. doi: 10.1128/jb.95.6.1987-1992.1968. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Singleton P. W., El Swaify S. A., Bohlool B. B. Effect of salinity on Rhizobium growth and survival. Appl Environ Microbiol. 1982 Oct;44(4):884–890. doi: 10.1128/aem.44.4.884-890.1982. [DOI] [PMC free article] [PubMed] [Google Scholar]