Mineral uptake by soybean (Glycine max [L.] Merrill) seeds during deve
lopment can significantly affect seed quality and value. Little is kno
wn about seed mineral transport mechanisms and control processes, alth
ough it is clear that each mineral displays a characteristic accumulat
ion pattern. ion-specific accumulation patterns could result from chan
ges 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 cultur
e was examined during seed development. Sr2+ and Rb+ were used as tran
sport 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-cultur
ed embryo Sr2+ and Rb+ uptake rate trends differed: Rb+ uptake increas
ed with seed fresh weight, whereas Sr2+ uptake rates remained constant
or decreased slightly. Ovule Sr2+ influx data suggest that the pod an
d seed coat impose a transport barrier that could account for the rela
tive decline in embryo Ca2+ content during development.