Source, sink and hormonal control of translocation in wheat.

An analysis of the pattern of movement of (14)C-labelled flag leaf assimilates in wheat (Triticum aestivum l. c.v. Gabo) during grain development, indicated that the greater the requirement for assimilates by the ear the more rapid was the speed of movement of these through the peduncle to the ear and also the lower their concentration. Experiments with [(14)C] indoleacetic acid ([(14)C]IAA) suggested that auxin production by the grains was not responsible for the control of assimilate translocation through the peduncle. Limiting the supply of available assimilates by shading the lower parts of the plant, did not significantly alter the speed of movement of (14)C-photosynthate through the peduncle, while severing half of the vascular tissue in the peduncle altered the pattern of movement of (14)C to the ear and enhanced the speed of movement of (14)C through the remaining functional conducting tissue. These results are discussed in relation to the mechanism of translocation.