Physiological effects of laxogenin C on increasing the resistance todrought stress of cucumber seedlings

【Objectives】The chemical structure of laxogenin C(LG-C)is similar to the teasterone of brassinosteroids, which plays important roles in regulating plant growth. Both the compounds contain 3-aglycone-6-ketone functional groups of brassinosteroids(BRs), show bioactivity of plant hormone. LG-C is easily prepared in low cost, so more suitable to be used as plant growth regulator. The physiological effects of LG-C on cucumber seedlings under drought stress were studied in this paper to lay a foundation for the prospective practical use.【Methods】 Using cucumber seedlings as test materials, the effect of foliar spraying LG-C was studied using a pot experiment. Three percentages of field water capacity in growth substrates were set up as: 80%(CK), 60%(light stress)and 50%(heavy stress). LG-C(0.05 mg/L)was foliar sprayed when the seedling leaves were fully expanded. Each spray volume was 20 mL per seedling and the spray was conducted for 7 days successively, with spraying water as control for the two water stress treatments. The contents of physiological and bioactive compounds were measured immediately after the last spraying. 【Results】Compared with no LG-C treatment, under the light water stress, the contents of soluble protein, free proline, soluble sugar in the leaves of cucumber seedlings were increased by 21.06%, 41.75% and 29.65% respectively; the contents of chlorophyll a, chlorophyll b, carotenoid were increased by 26.83%, 13.33% and 23.21% respectively. The activities of superoxide dismutase, peroxidase and catalase were enhanced by 10.06%, 19.34% and 33.08% respectively. The electrolytic leakage, malondialdehyde content, autoxidation rate, water loss rate were decreased by 10.16%,30.68%,22.48% and 9.69%, respectively. Under heavy drought stress, the contents of soluble protein, free proline, soluble sugar in the leaves of cucumber seedlings were increased by 19.35%, 37.05% and 25.23% respectively. The contents of chlorophyll a, chlorophyll b, carotenoid were 28.17%, 20.00% and 28.42% higher respectively. The activities of superoxide dismutase, peroxidase and catalase were enhanced by 6.03%,37.10% and 30.72%, respectively. The electrolytic leakage, malondialdehyde content, autoxidation rate, water loss rate were decreased by 10.15%,47.10%,16.97% and 8.85%, respectively.【Conclusions】Exogenous LG-C may improve cucumber drought resistance by increasing the antioxidant activities, osmotic adjustment substances, chlorophyll content and water holding capacity.