Adaptation to Water Stress in Wheat

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Abstract
Three experiments were designed to investigate to what extent adaptation to water stress take place. Wheat (Triticum aestivum L. cv. Kolibri) was grown in water culture at constant temperature, air humidity, and light intensity. When the plants were 16 days old, the potential of the root medium (ψr) was lowered by 1 bar every second day by means of polyethyleneglycol 1500 down to −4 or −7 bar and then remained at these levels. As a control one experiment was grown at −0.7 bar. By regression it was found that when ψr was lowered by I bar, osmotic potential in leaf (ψπ) decreased 1.46 bar, and leaf water potential (ψt) 0.68 bar, which mean an increase of turgor of 0.78 bar. At the same time the leaf water content did fall 0.30 g per g dry matter. Specific transpiration rate increased significantly after ψr was kept constant, but the increase in area of fresh leaves was strongly reduced due to wilting of old leaves. After an “adaptation” period during which ψr remained at −0.7, −4, and −7 bar, respectively, for at least 1 week. ψr was altered so as to cover the range from 0 to −14 bar and ψπ, ψr, transpiration and diffusion resistance in stomata (rs) were measured. The levels of ψπ and ψ1 were lower (more negative) and turgor potential higher in plants grown at low ψr. The transpiration in pre-stressed plants showed less sensitivity to the alteration of ψr than in the non-stressed plants. The values of ψr at which rs increased greatly, were found to be about −13, −15, and −18 bar for plants grown at −0.7, −4, and −7 bar, respectively.