Physiological effects of laxogenin C on increasing the resistance to drought 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.
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