Translocation of Labelled Assimilates in the Soybean II. The Pattern of Translocation in Intact and Defoliated Plants

Abstract

The distribution of C14 -labelled assimilate in the soybean has been studied, emphasis being placed on the expanding leaf as the major apical sink. The expanding leaf imports assimilate from leaves be-low, this import rising to a maximum and then falling to almost zero when the leaf is half-expanded, At this stage in the growth of the leaf, it has begun exporting assimilate to the younger leaves. Export, both to younger leaves and down the stem to the root, increases until the leaf is fully expanded. The expanded leaves may also import assimilate to a very slight degree. Export of assimilate from an expanded leaf to the apex and root is inversely proportional to its distance from these sinks. The concentration in the stem of labelled assimilate derived from one source leaf decreases with distance from the source leaf; if derived from four source leaves the concentration fluctuates with maxima at the nodes. Defoliation between the source leaf and the root causes more assimilate to move to the root and less to the apex.