| Low temperature inhibits plant's normal growth and causes harm in varying degrees. Improving the cold tolerance of plant and reducing the adverse effects resulted from external environment becomes the focus of the plant's cold hardiness study. Many predecessors had done a lot of work on the research of spraying foreign materials to improve cold hardiness of crop, but the component of the preparations was too single, high residue and toxic effects. Composite exogenous substances which includes a variety of biological material has low residue rate. This research uses a kind of composite exogenous substances to study physiological mechanism how to improve cold tolerance of the plant and application scopes. The results were as follows:1 Under the low-temperature condition, spraying the composite exogenous substances diluted 600 times could significantly improve the cold tolerance of the cucumber seedlings. But spraying the plant the 400 times dilution of composite exogenous substances would be poisonous.2 Under the low-temperature condition, in advance of spray composite exogenous substances could protect plant, reduce cold stress, and make it quickly resume its growth in the number of leaves, plant height, fresh weigth after return to normal growth level.3 Under 10℃, the composite exogenous substances could improve the cucumber leaves the content of soluble sugar, soluble protein and proline., enhancing the activity of SOD, strengthen the capability of scavenging O2- and H2O2 producted by the adversity , decrease the MDA output and reduce the poison to cells, moreover, solute concentration in leaves increased, stabilize the membrane penetrability.4 Under 10℃, the composite exogenous substances improved tomatoes, peppers and summer squash after resume growth on the number of leaves, height, fresh weight and dry weight. But the result indicated that the effect of biological preparation on tomatoes was better than summer squash and peppers.
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