The Influence of Sucrose and Abscisic Acid on the Determination of Grain Number in Wheat

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Abstract
Using detached ears of wheat cultured in nutrient solution the effect of sucrose and ABA supply on grain number was examined. In ears detached prior to ear emergence, to correspond with the time of pollen mother cell meiosis, higher levels of sucrose uptake were associated with higher grain number per ear. ABA indirectly caused a reduction in grain number by decreasing uptake of sucrose through decreasing stomatal conductance and transpiration. There was possibly also a direct effect of ABA on grain number. At higher levels of ABA the negative effect on grain number was decreased by increasing the sucrose concentration. In ears detached one to three days after anthesis grain number was also influenced by the amount of sucrose taken up. although grain number was not as sensitive to the sucrose supply at this time as it was at meiosis. The influence of ABA following anthesis was limited to an indirect effect on grain number through reductions in sucrose uptake.