Ontogenetic changes in root nodule subpopulations of common bean (Phaseolus vulgaris L.). II. Protein content and carbohydrate pools
1993
Vikman, P.A. | Vessey, J.K.
Root nodules of common bean (Phaseolus vulgaris L. GN 1140) show different ontogenetic patterns of nitrogen fixation in different parts of the root system. The objective of the present study was to search for nodule physiological factors which could explain these differences. Plants were grown to maturity under controlled environment conditions. Root nodules were regularly harvested from two zones of the root system, and assayed for soluble cytosolic content and carbohydrate status. Nodule concentrations of soluble carbohydrates, glucose, fructose or sucrose, did not change significantly during the pod-filling decline in nitrogenase activity. Nodule concentrations of sucrose appeared more related to nodule ontogeny than to the ontogenetic stage of the shoot. Total soluble protein and leghaemoglobin concentrations were highly correlated to nitrogenase activity. In the top zone of the root system proteolytic capacity increased during pod-filling, indicating a role in nodule senescence. Proteolytic capacity also increased in the mid zone, but to a lesser extent, and without correlation to nitrogenase activity. The two nodule subpopulations showed different nitrogenase activity in relation to their leghaemoglobin and carbohydrate status. We suggest that physiological differences within the root nodule subpopulations, possibly in combination with the distance from the shoot, makes the top zone more susceptible to a systemic increase in proteolytic capacity during rapid pod-filling.
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