In vitro Sucrose Uptake and Starch Synthesis by Isolated Wheat (Triticum aestivuim) Grains

ABSTRACT The aim of this study was to establish and optimise a simplified method of halved grain culture, in order to utilise it to evaluate the ability of isolated sinks (developing wheat grains) in sucrose uptake and conversion (defined by sink strength) under unlimited source conditions. Both sucrose uptake and starch synthesis increased linearly over the incubation periods used in this study. A biphasic pattern of sucrose uptake in response to external sucrose concentrations was evident. Starch synthesis also increased curvilinearly with respect to external sucrose concentration. 2,4-dinitrophenol (DNP)) inhibited both sucrose uptake and starch synthesis. An increase in pH from 6.5 to 8 reduced both sucrose uptake and, to a lesser extent, starch synthesis. From these observations, a metabolically active uptake of sucrose by endosperm cells concomitant with a diffusional influx of sucrose into the endosperm cells were both evident. The relative importance of both the active and diffusional movement of sucrose and the importance of transport across the plasma membrane is discussed in the text.