|Sheng, Chuxing - (DECEASED) 3611-05-00|
Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 21, 1996
Publication Date: N/A
Interpretive Summary: Increasing biological nitrogen fixation by legumes, such as soybean, is important in terms of limiting the requirement for nitrogenous fertilizer application for optimum crop production and contributing to the concept of sustainable agriculture. The process of biological nitrogen fixation occurs in specialized structures (termed nodules) which form on roots of legumes in association with a beneficial bacteria. In this study it was shown that nodule development is controlled by signal compound(s) which are synthesized in the leaves and are translocated to the root. Knowledge of this chemical signal involvement in nodulation control is projected to allow manipulation of nodule development with the goal of increasing biological nitrogen fixation by soybean. Confirming the leaf as the synthesis site of a signal capable of controlling nodulation is important to scientists seeking pathways which may be manipulated at the genetic or molecular level to enhance biological nitrogen fixation by legumes. Successful enhancement of biological nitrogen fixation will decrease the need for application of expensive nitrogenous fertilizers to other crops grown in rotation with legumes, and will minimize the environmental impact of nitrogenous fertilizer application.
Technical Abstract: Grafting studies involving Williams 82 (normally nodulating) and NOD1-3 (hypernodulating) soybean (Glycine max [L.] Merr.) lines and Lablab purpureus were used to evaluate the effect of shoot and root on nodulation control and plant growth. A single- or double-wedge graft technique, with superimposed partial defoliation, was used to separate signal control from photosynthate supply effect. Shoot and root dry-matter production was less for NOD1-3 than for Williams 82 in all graft combinations. Grafting of two shoots to one root enhanced root growth in both soybean genotypes, but not in Lablab purpureus. Root genotype had little impact on shoot growth. Removing trifoliolates from either Williams 82 or NOD1-3 shoots decreased root and shoot dry matter, attributable to decreased photosynthetic source. In double-shoot, single-root grafted plants, defoliation of the Williams 82 shoot increased nodule number, while defoliation of the NOD1-3 shoot led to decreased nodule number, on both soybean and Lablab purpureus roots. This study demonstrated that 1) soybean leaves are the dominant site of autoregulatory signal production which controls the final number of nodules; 2) difference in root and shoot growth between Williams 82 and the hypernodulating mutant is genetically controlled and not modified by a translocatable signal; and 3) seedling vegetative growth and nodule number are independently controlled.