The Responses of Leaf Water Potential and Leaf Diffusive Resistance to Abscisic Acid, Water Stress and Low Temperature inHibiscus esculentus: The Effect of Water Stress and ABA Pre-Treatments

Abstract

Eamus, D. 1986. The responses of leaf water potential and leaf diffusive resistance to abscisic acid, water stress and low temperature in Hibiscus esculentus: the effect of water stress and ABA pre-treatments.—J. exp. Bot. 37: 1854-1862. Intact plants of okra (Hibiscus esculentus) were chilled at 6 °C in the light, and leaf diffusion resistance (LDR) and leaf water potential measured. The response of the LDR of excised leaves to fresh weight loss and, separately, exogenous abscisic acid (ABA) supply, was also studied at 6 °C and 30 °C. The influence of two pre-treatments upon these measurements was studied. The two pre-treatments consisted of the imposition of a period of water stress at 30 °C prior to measurement (followed by re-watering) or the spraying of the leaves with ABA. It was found that plants that had been grown in a high humidity environment continuously (designated control plants) had stomata that were very unresponsive to both water loss from the leaves and to exogenous ABA at both temperatures (6 °C and 30 °C). Chilling the control plants resulted in rapid wilting and concomitant decline in leaf water potential. A pre-treatment of water stress prior to chilling did not alter or reduce the rate of development of chilling injury, nor did the pre-treatment increase the responsiveness of stomata at 6°C to water loss or exogenous ABA. However, spraying the leaves with ABA prior to chilling reduced the severity and delayed the onset of chilling injury. Stomatal response to water stress and exogenous ABA was increased by the spraying pre-treatment. These results are discussed in relation to previous studies of the phenomenon of stomatal locking open at low temperature and the effect of pre-treatments upon the development of chill-resistance.