Water Potential, Growth, and Polyribosome Content of the Stressed Wheat Apex

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Abstract
The effect of drought on the growth, ribosomal content, and water potential of the immature floral apex of wheat plants was studied under controlled environment conditions. During drought the water potential of the apex (measured with a thermocouple psychrometer) decreased at approximately the same rate as that of expanded leaves. Elongation and differen tiation of the floral apex ceased at approximately −12 × 105 Pa and the polyribosomal content decreased from 50% of the total ribosomal population to less than 10%. At this water potential also, elongation of expanding leaves was severely inhibited. With continued drought the water potential of the apex continued decreasing. The exposed leaves died at a water potential of about −35 × 105 Pa but the apex was still alive at a water potential of −60 × 105 Pa and after rewatering it eventually resumed growth.