EFFECT OF WATER DEFICIT AND APPLICATION OF 24-EPIBRASSINOLIDE ON GAS EXCHANGE IN CAULIFLOWER PLANTS

Under partly controlled greenhouse conditions, an experiment was initiated to monitor the long-term effect of water deficit and the effect of the application of 24-epibrassinolide on the photosynthesis and transpiration rates. The model plant was cauliflower, the Chambord F1 variety. The cauliflower plants were grown in pots with a volume of 15 l, at the temperature of 25 °C during the day and 18 °C at night. The cauliflower plants were irrigated with Knop’s nutritional solution once a week and with distilled water on the remaining days of the week. The plants were provided with a solution containing micro-elements according to Benson twice during the vegetation period. Irrigation was controlled according to the results obtained by the apparatus AT Theta Kit (Delta – T Device, the United Kingdom). The experiment plan contained 4 groups. The first group was the control group, irrigated with 25% of full water capacity (FWC); the second group was a stressed group. In this group, irrigation was limited to 20% of FWC throughout the vegetation period. In the third and fourth groups, 24-epibrassinolide in the concentration of 10^–9 M was applied to the third and fourth groups with control plants and stressed plants at the stage of 6–7 leaves. It follows from the results obtained that water deficit provably reduces the rate of exchange of gases in cauliflower plants in comparison to the irrigated control group. The application of 24-epibrassinolide in the control plants reduced the photosynthesis and transpiration rates apparently due to unbalanced endogenous level of phytohormones. As opposed to that, in the stressed plants, the application of the tested substances increased the photosynthesis rate and reduced the transpiration rate in comparison to the untreated stressed plants. It is apparent from the abovementioned findings that the application of 24-epibrassinolide reduces the transpiration rate in the monitored plants and has an effect similar to that of abscisic acid. Thus, it can be stated that in this case, it is an anti-transpiration effect