Respiration and Carbohydrate Accumulation in the Water-Stressed Wheat Apex

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Abstract
The effect of water stress on the respiration of the immature floral apex of wheat was studied in a controlled environment and related to changes in water relations, growth, protein synthesis, and solute accumulation. Apex respiration measured in vitro polarographically showed no wounding response and was cyanide- and malonate-sensitive. It decreased with each decrease in apex water potential Φa reaching 40% of the non-stress control rate at −5·0 MPa, irrespective of whether the water stress was induced by droughting in vivo or non-permeating osmotica in vitro. Apex respiration was not quantitatively related to turgor potential. During drought stress there was a conservation of ethanol-insoluble dry matter and water in the apex while ethanol-soluble carbohydrates and amino acids accumulated. The calculated daily import of soluble carbohydrate into the apex during the whole drought stress period remained nearly constant despite falling water potential. Respiration of the apex during a drought period was not limited by the suistrate supply within the apex.
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