PHYTOHORMONAL REGULATION OF GASES EXCHANGE IN BETA VULGARIS L. DURING WATER STRESS

The paper assesses the impact of abscisic acid (ABA) and cytokinin benzylaminopurine (BAP) on the control of exchange of gases in the leaves of sugar beet during water stress. The pot experiments with young plants of the Takt variety were carried out under controlled conditions in a greenhouse. ABA in the concentration of 100 μM and BAP in the concentration of 1 μM and 10 μM were applied to the leaves 3 days after the plants were divided into variants and after irrigation was interrupted. The relative water content (RWC) in leaves, the photosynthetic rate (PN), the transpiration rate (E) and the water use efficiency (WUE) were measured just before the application of the growth regulators and then 2 hours and 1, 3, 5, 7 and 9 days after the application of the growth regulators. Throughout this period, the plants retained high RWC but there was a statistically significant decrease of PN and E and also an improvement of WUE in comparison with the non-stressed plants. The application of ABA first decreased PN and E in the stressed plants, and deterioration of WUE occurred (2 and 24 hours after the application). At later dates, the levels of PN and E obtained by measurement were, conversely, higher and WUE was approximately the same in comparison with the plants that were stressed but not treated with ABA. The application of BAP on plants stressed by drought resulted, throughout the monitored period, in statistically significantly higher levels of PN and E in comparison with the plants not treated by BAP. In the case of joint application of both substances, the identified levels of PN and E were statistically provably higher than when ABA was applied alone; these levels were almost the same as the levels measured after the application of BAP alone