PLANT PHYSIOLOGY , Vol 104, Issue 3 937-944, Copyright © 1994 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Changes in Soybean Fruit Ca2+ (Sr2+) and K+ (Rb+) Transport Ability during Development
J. A. Laszlo
Food Physical Chemistry, United States Department of Agriculture-Agricultural Research Service, National Center for Agricultural Utilization Research, Peoria, Illinois 61604
Mineral uptake by soybean (Glycine max [L.] Merrill) seeds during
development can significantly affect seed quality and value. Little is
known about seed mineral transport mechanisms and control processes,
although it is clear that each mineral displays a characteristic
accumulation pattern. Ion-specific accumulation patterns could result from
changes in source availability, in transport kinetics through the seed pod
and seed coat, or in the mineral uptake capability of the embryo. Ca2+ and
K+ have negligible and high phloem mobilities, respectively. Ca2+
accumulation lags behind dry matter (C and N) and K+ accumulation in
soybean embryos. To eliminate source availability influences, the Ca2+ and
K+ uptake ability of isolated embryos and of seeds in pod culture was
examined during seed development. Sr2+ and Rb+ were used as transport
analogs of Ca2+ and K+, respectively. Sr2+ and Rb+ uptake rates by isolated
embryos increased with seed fresh weight, indicating that the embryo was
not limiting Ca2+ accumulation. However, the pod-cultured embryo Sr2+ and
Rb+ uptake rate trends differed: Rb+ uptake increased with seed fresh
weight, whereas Sr2+ uptake rates remained constant or decreased slightly.
Ovule Sr2+ influx data suggest that the pod and seed coat impose a
transport barrier that could account for the relative decline in embryo
Ca2+ content during development.
