Translocation of Assimilates Within and Between Potato Stems

Three aspects of translocation in potato were examined: (i) translocation within stems (ii) translocation between individual stems of a plant (iii) translocation between tubers following injection of 14C sucrose into a single daughter tuber. Assimilates exported from single leaves of evenly illuminated potato stems remained confined to the same side of the stem as the source leaf in a pattern consistent with the internal arrangement of vascular bundles in the stem, and tubers borne on stolons vertically below the source leaf contained higher concentrations of 14C than those on the opposite side. Consequently 14C import into the tubers bore little relationship to tuber growth rates. However, alteration of source/sink relations by pruning stems to a single souce leaf resulted in an even distribution of 14C throughout the vascular bundles of the stem and 14C import into the tubers bore a stronger relationship to tuber growth rates than to the phyllotactic relationship of the tubers with the source leaf. Labelling one stem of a potato plant resulted in little or no movement of 14C into tubers on other unlabelled stems. However, removal of the unlabelled stems at ground level induced a significant movement of 14C from the labelled stem to the tubers on unlabelled stems, this movement occurring via the mother tuber. Shading the unlabelled stems had less effect than stem removal. 14C sucrose injected into single daughter tubers was translocated to other tubers on the same stem and also to tubers on a second stem at the opposite end of the mother tuber. The sucrose was converted to starch in these tubers. The results favour the view that each potato stem functions as an independent unit with potential for assimilate redistribution within a stem but with little or no carbon exchange occurring between stems, unless under severely altered source/sink patterns.