Changes in Internal Water Relations and Osmotic Properties of Leaves in Maturing Soybean Plants

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Abstract
The changes in the internal water relations of soybean (Glycine max L. Merr.) leaves during vegetative and reproductive growth were studied by following the changes in the pressure-volume curves of soybean leaves. The results demonstrate that soybean leaves undergo a change in their osmotic properties which coincides with the onset of active reproductive growth and is not induced by water stress. The observed osmotic changes resulted in an increase in the leaf relative water content at any given bulk leaf water potential. The volume of leaf water loss needed to reduce turgor potential to zero did not change following this change in osmotic properties. The degree of turgor maintenance after the change in osmotic properties depended on the ability to maintain adequate leaf relative water content. The observed changes in bulk osmotic potential of the soybean leaves would contribute to increased leaf-soil water potential gradients and therefore to improved ability to extract the remaining soil water as the season progressed.