Stress-induced declines in soybean N2 fixation are related to nodule sucrose synthase activity

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Type Article
Original languageEnglish
Pages (from-to)937-946
JournalPlant Physiology
Issue number3
Publication statusPublished - 1997
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Soybean (Clycine max L.) plants were subjected to a number of treatments (drought, 1 O mM nitrate, 150 mM NaCI, shoot meristem removal, and removal of approximately 50% of the nodules) to test the hypothesis that metabolic responses contribute to the regulation of N, fixation. Nitrogenase activity was correlated with the activity of nodule sucrose synthase (SS), but not with that of glutamine oxoglutarate amino transferase. Leghemoglobin levels and other
enzyme activities were not significantly or consistently affected by the treatments. SS mRNA was greatly reduced in nodules of drought-, salt-, and nitrate-treated plants; however, this was not correlated with changes in soluble carbohydrate, starch, amino acids, or ureides. Leghemoglobin mRNA was only slightly affected by the treatments. The time course of drought stress showed a
decline in the SS transcript leve1 by 1 d, but levels of leghemoglobin,
glutamine synthetase, and ascorbate peroxidase mRNA were not markedly affected by 4 d. SS activity at 4 d was reduced by 46%. We propose that N, fixation in soybean nodules is mediated by both the oxygen-diffusion barrier and the potential to metabolize sucrose via SS. The response to environmental perturbation may involve down-regulation of the nodule SS gene.