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

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.