Anatomical Changes in Leaves of Puma Rye in Response to Growth at Cold-Hardening Temperatures

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Abstract
Rye plants were cold hardened by growth at 4/2.degree. C day/night (D/N); unhardened control plants remained at 25/20.degree. C D/N. Leaves from hardened plants contained 33% less water on a dry weight basis than those from unhardened plants. The osmolar concentration of expressed sap from hardened leaves was 1.5 times greater than that of unhardened leaves. The number of cell layers in fresh leaves remained constant, but leaves from hardened plants were about 1.5 times thicker than those from unhardened plants. Increased leaf thickness was caused by increased mesophyll cell size. The structure of the vascular bundle and both stomatal frequency and distribution patterns of the upper and lower epidermal surfaces were altered.