PLANT PHYSIOLOGY , Vol 114, Issue 2 687-693, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Allocation of S in Generative Growth of Soybean
Sunarpi and J. W. Anderson
School of Botany, La Trobe University, Bundoora, Victoria 3083, Australia
Soybean plants (Glycine max L. Merr) were grown with 100 [mu]M S and 15 mM
N and studied with respect to S allocation during grain development. The
grains accounted for 87% of the S taken up after d 42, the balance coming
from internal redistribution of S from leaves and pods. Detailed studies of
the leaves, pods, and grains associated with leaf axils 6 and 7 showed that
sulfate accumulated in the pods as they expanded to 50% of full length,
ahead of grain enlargement, but declined to very low levels as grain growth
commenced. Conversely, homoglutathione (hGSH), cysteine, and methionine
increased. In developing grains, hGSH accounted for 60 to 90% of the
soluble-S but sulfate was barely detectable. The data are consistent with a
model in which, under S-limiting conditions, the pods act as sinks for
sulfate and grain growth initiates the assimilation of sulfate into hGSH in
the pods, and then into developing grains, where it is incorporated into
grain proteins.
