PLANT PHYSIOLOGY , Vol 110, Issue 4 1151-1157, Copyright © 1996 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Distribution and Redistribution of Sulfur Supplied as [35S]Sulfate to Roots during Vegetative Growth of Soybean
Sunarpi and J. W. Anderson
School of Botany, La Trobe University, Bundoora, Victoria 3083, Australia
Soybean (Glycine max L.) plants were grown in nutrient solution containing
10 [mu]M sulfate and were treated at various times with [35S]sulfate for 48
h. Growth was then continued in unlabeled solution. The sulfur content of
each leaf increased rapidly until it was about 40% expanded; small,
additional increases occurred until the leaf was about 70% expanded after
which the sulfur content decreased by about 50%. Leaves that were about 60
to 70% expanded during the pulse were strongly labeled but then underwent a
significant loss of 35S label. Leaves that were in the early stages of
expansion imported little 35S label during the pulse but acquired 35S label
during the chase period as they expanded (i.e. redistribution). Most of the
redistributed 35S label was derived from other leaves. The rates of both
sulfur import and sulfur export by a leaf were greatest at about 70%
expansion. Leaves that acquired 35S label during early development retained
a much higher proportion of their label than leaves that were more
developed, suggesting that the sulfur acquired by leaves during early
development is preferentially incorporated into a pool that is less mobile
than the sulfur acquired in the later stages of leaf growth.
