Studies On Effects Of Ca～(2+) On Carbon And Nitrogen Metabolism In Cucumber Seedlings Under Hypoxia Stress

Hypoxia stress in the root-zone is thought be a major determinant in the adverse effect of O₂ deficiency in hydroponic culture and root-cushion formation in substrate culture on plant species. Now hypoxia stress has become a limited factor of soilless culture application to large area production. Therefore, improving the hypoxia tolerance of plants plays a vital role in soilless culture. As a major element necessary for plant growth and a second messenger of coupling extracelluar signal and intracellular physiological reactions, calcium (Ca²⁺) plays a crucial role in regulating physiological reactions under environment stress. It has been known that [Ca²⁺]_cyt increase rapidly under environmental stress and Ca²⁺.CaM compound formation after Ca²⁺ combined with target enzyme CaM. It could relieve the harm of stress to the crops by regulating gene expression and inducing change of physiological and biochemical metabolism under environmental stress. Plants have evolved mechanisms for sensing oxygen shortage and adjusting their cellular metabolism to adapt for oxygen deprivation. But little is known about the effect of exogenous Ca²⁺, Ca²⁺ and CaM inhibitor on cucumber seedlings tolerance under hypoxia stress, and whether Ca²⁺, CaM are involved in the regulation hypoxia tolerance of cucumber seedlings.In the present study, hypoxia-tolerant cucumber cultivar 'Lubachun No.4' and hypoxia- sensitive cultivar 'Zhongnong No.8' were chosed as experimental materials, and were cultivated hydroponically in nutrition solution exposed to hypoxia stress by precisely controlling dissolved oxygen in nutrition solution through dissolved oxygen controller, combined with exogenous foliar spraying La³⁺, EGTA, adding exogenous Ca²⁺ and TFP to the nutrition solution to investigate the effect of Ca²⁺, CaM on intrinsic hypoxia resistance of cucumber seedlings and elucidate the relationship between Ca²⁺, CaM and enhanced hypoxia resistance and the respiratory, nitrogen and carbohydrate metabolism. Main research results were as follows:Under hypoxia treatment, the activities of LDH, PDC, ADH, SOD, POD and CAT, contents of lactate, acetaldehyde and ethanol increased significantly, activities of IDH and SDH decreased significantly in roots of the two cultivars under hypoxia stress. Compared...