THE EFFECTS OF GLAUCOUSNESS, EPICUTICULAR WAX, LEAF AGE, PLANT HEIGHT, AND GROWTH ENVIRONMENT ON WATER LOSS RATES OF EXCISED WHEAT LEAVES

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Abstract
Water loss at minimum stomatal aperture (residual transpiraiton) from plant surfaces accounts for a substantial proportion of total transpiration during periods of water stress and at night. Its reduction by genetic selection has been suggested as a desirable objective in water-limited environments. To identify genetic and environmental sources of variation in residual transporation of variation in residual transpiration of wheat (Triticum spp.), the effects of glaucousness, epicuticular wax, leaf age, plant height, and growth environment were determined using excised leaves. Glaucousness reduced residual transpiration by an average of 10%. Differing quantities of epicuticular wax and glaucousness in an isogenic pair of genotypes affected residual transpiration as well, the rate being 33% greater in the low wax, nonglaucous than in the high wax, glaucous line. residual transpiration rate of flag leaves of field-grown plants increased with leaf age, particularly during the 7 d following ligule appearance. The rate of residual transpiration was greater in tall than in dwarf near-isogenic lines. Residual transpiration of leaves from plants grown in glasshouses was 44-66% lower than that of plants grown outdoors, which had a mean rate of 2.68 .times. 10-5 g H2O cm-2 min-1. Method of water application to glass-house plants influenced residual transpiration rate. The rate for leaves of plants watered by spraying water onto the plant and soil surface was 20% greater than that of leaves of plants watered on the soil surface only. It was concluded that the increase in residual transpiration rate with leaf age was due to duration of exposure to the rigors of the exterior environment; the absence of this in controlled environments results in lower rates of residual transpiration than in the field.