Influence of Xylem Water Potential on Leaf Elongation and Osmotic Adjustment of Wheat and Lupin

Abstract

The leaf elongation rate and osmotic pressure at full turgor of wheat (Triticum aestivum L.) and lupin (Lupinus cosentinii Guss.) were measured in well watered plants, in plants that were allowed to dry the soil slowly over 7 d, and in plants in which the water potential of the leaf xylem was maintained high by applying pressure to the roots during the drying cycle. Maintenance of high xylem water potentials failed to prevent a reduction in the rate of leaf elongation as the soil dried, while the osmotic pressure at full turgor and the degree of osmotic adjustment increased as the soil water content decreased. The rate of leaf elongation was reduced more and the degree of osmotic adjustment was higher in leaves with high xylem water potentials than in those in which leaf xylem potentials were allowed to decrease as soil water content decreased. Osmotic adjustment was linearly correlated with the reduction in leaf elongation rate in both wheat and lupin.