Water Potential, Translocation and Assimilate Partitioning

Lang, A, and Thorpe, M. R. 1986. Water potential, translocation and assimilate partitioning.—J. exp. Bot. 37: 495-503. The effect of water status upon translocation and assimilate partitioning is examined both from theory and in an experiment with young Phaseolus plants. Theory predicts that translocation is unlikely to be directly affected by water status. However, water potential differences within plants should influence translocation flow, with regions at lower potentials attracting disproportionately large shares of assimilate. This prediction is supported in the experiment with Phaseolus in which the pattern of partitioning in the root changed rapidly in response to bathing portions of it in solutions of different osmolarity. The relevance of these findings to the growth of plants under natural conditions is considered and evidence is presented that water potential gradients may be an important factor in the control of partitioning. Key words-— Phloem translocation, xylem transport, partitioning, water potential, control, osmotic potential. Correspondence to: Physics and Engineering Laboratory, DSIR, Private Bag, Lower Hutt, New Zealand.