The After‐Effect of Water Stress on Transpiration Rate and Changes in Abscisic Acid Content of Young Wheat Plants

Abstract Young wheat plants (Triticum aestivum L. cv. Weibulls Starke II) were exposed to water stress for 1, 2 or 3 hours by cooling the roots. The plants were subjected to a constant water stress during the stress periods. By this treatment the leaf water potential was lowered from −6.5 to −11.5 bars. Leaf water potential, transpiration rate and abscisic acid content were determined during the stress periods and during the recovery. The water stressed plants showed an after‐effect on transpiration rate lasting for between 10 and 24 hours depending on the duration of the stress. The amount of water stress in the stressed plants compared with the controls is defined as the difference in leaf water potential between the controls and the stressed plants during the stress period integrated over time. The amount of after‐affect on transpiration is analogously defined as the difference in transpiration rate between the controls and the stressed plants during the recovery period integrated over time. There was a linear relationship between the amount of water stress and the amount of after‐effect on transpiration of the leaves. The abscisic acid content of the leaves increased between 3.0 and 4.5 times the original content depending on the duration of the stress. However, during the recovery the abscisic acid content reattained the pre‐stress level within 3 hours for all three stress periods. There was thus no direct relationship between the after‐effect and the abscisic acid content of the leaf.