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. 1987 Feb;83(2):341–348. doi: 10.1104/pp.83.2.341

Regulation of Assimilate Partitioning in Soybean 1

Initial Effects following Change in Nitrate Supply

J Kevin Vessey 1, David B Layzell 1
PMCID: PMC1056359  PMID: 16665247

Abstract

Increased concentrations of nitrate in a nutrient solution (2, 5, and 10 millimolar KNO3) were correlated with increased shoot:root ratios of non-nodulated soybeans (Glycine max [L.] Merr.) grown in sand culture. While altering the pattern of C and N partitioning, the N treatments did not affect whole plant photosynthesis over the study period. To determine the mechanism responsible for the observed changes in assimilate partitioning, detailed C and N budgets were worked out with plants from each N treatment over three consecutive 4-day periods of midvegetative growth. The information for the C and N budgets from the 2 and 10 millimolar NO3− treatments was combined with data on the composition of xylem and phloem exudates to construct a series of models of C and N transport and partitioning. These models were used to outine a `chain-reaction' of cause-and-effect relationships that may account for the observed changes in assimilate partitioning in these plants. The proposed mechanism identifies two features which may be important in regulating the partitioning of N and other nutrients within the whole plant. (a) The concentration of N in the phloem is highly correlated with the N concentration in the xylem. (b) The amount of N which cycles through the root—from phloem imported from the shoot to xylem exported by the root—is regulated by the root's requirement for N: only that N in excess of the root's N requirements is returned to the shoot in the xylem. Therefore, roots seem to have the highest priority for N in times of N stress.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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