Effects Of Exogenous Calcium On The Growth, Photosynthesis And Soluble Protein Expression Of Cucumber Seedlings Under Hypoxia Stress

Cucumber (Cucumis sativus L.) is as one of key vegetable for soilless culture in China due to good economic returns, fast growth, high production and the length period of supply. Cucumber is sensitive to hypoxia stress in cultivation and production. Oxygen deficiency in the root-zone and root-cushion formation has to be as the crucial limitation factors of cucumber development and production.Crops tolerance has been enhanced by applying exogenous Calcium in cultivation and production. Calcium is the essential element of plant growth and development. Calcium which integrates environmental signal and intracellular physiological reaction is involved in regulating plant growth and development under normal condition and plant adaptation response to abiotic stress. Under abiotic and biotic stress condition, the content of Ca2+in cell is significantly increased and the formation of Ca2+-CaM compound occurs. Calcium has a function to activate ATPase, enhance the transport of photosynthetic production, and regulate the expression of gene and protein in tissues. Calcium, therefore, exert a key role in regulating plants adaptation response to various stress.Using cucumber cultivars’Zhongnong No.6’which are sensitive to hypoxia stress as materials and tight control of dissolved oxygen in nutrient solution through dissolved oxygen controller, we selected suitable Ca+concentrations for foliar spray or by adding to the nutrient solution, we investigated the effects of exogenous calcium on effects of plant growth, photosynthesis and protein content and expression. Main results were as the following:1. Increased biomass of cucumber seedlings, impoved the growth of shoot and root and lighten the damage effect of cucumber seedlings were obtained by applying10mmol-L-1CaCl2on leaves or maintaining8mmol·L-1CaCl2concentration in the nutrient solution increased under hypoxia stress. The seedlings displayed inhibited growth and development when higher concentration CaCl2(more than20mmol·L-1CaCL2in leaves and more than16mmol·L-1CaCl2in roots) was used. These results illustreated that appropriate concentration of Ca2+could regulate cucumber adapation response to hypoxia stress.2. Under hypoxia stress, Pn, Gs, Ci and Tr in ’Zhongnong No.6’ were decreased; Fv/Fm、Fv’/Fm’、ΦPSII. qP and Prate were reduced while qN、L (PFD) and Drate rose and Hy-Ca were increased. The amplitude of variation of all indexes was the highest when seedlings encourted hypoxia and calcium deficiency. The application of calcium in leaves and roots shortened the amplitude and appropriate concentration of calcium narrowed the fluctuation of photosynthesis and chlorophyll fluorescence and consequently minimized injury effect of hypoxia on plants growth and development.3. Under hypoxia stress, the plant growth and protein content was inhibited while those increased with high concentration calcium application in leaves or nutrition solution under hypoxia showed approaching tendency to the seedlings in control. The calcium application in nutrition solution is better than in leaves for the growth of cucumber seedlings under hypoxia stress. By SDS-PAGE electrophoresis analysis,132.0KD and16.8KD protein were increasing expressed in leaves under hypoxia, decreasing and even disappearing when8mmol·L-1Ca2+. It is the same as the expression of58.0KD protein in roots.