Effects Of Calcium On Photosynthesis In Cucumber Seedlings Under Hypoxia

In soilless culture, hypoxia stress come into appearance as a result of insufficient oxygen supply or root-cushion formation. For roots of all crops in soilless culture, oxygen deficiency is one of decesive obstacles. It is of great significance to explore channels of improving tolerance and resistance to hypoxia by biological means. Calcium, an indispensable element for plant growth and a second messenger for coupling extracellular signal and intracellular physiological reaction, witness a remarkable increase in cell and the formation of Ca²⁺ · CaM compound once suffering from stress, functioning as stability maintaining of cell wall, cell membrane and membrane proteins. In addition, calcium activates ATPase, facilitate the transport of photosynthetic production, regulate stomatal movement and oxygen-evolving activity. Calcium, consequently, plays an important role in alleviating damages by various stress.With two cultivars of cucumber(Cucumis sativus L) of discrepant hypoxia resistant capability, 'Zhongnong No. 8', a hypoxia-sensitive cultivar and 'Lvbachun No.4', a hypoxia-resistant one, we investigated the effects of calcium on seedling growth and photosynthesis in cucumber seedlings under hypoxia stress by controlling calcium concentration in nutrient solution, therefore, made it clear the physiological function of calcium in alleviating damages caused by hypoxia stress from photosynthetic aspect. The results are summarized as follows:Cucumber seedling growth was inhibited under hypoxia compared with the control, seen from the decreased fresh weight, dry weight, shoot dry weight and leaf area. High concentration of calcium narrowed the decrease span of dry weight, fresh weight and area of leaf effectively, 'Lvbachun No.4' found a better alleviation effect compared with 'Zhongnong No. 8'. Root length, root area and root volume dropped significantly under hypoxia compared with the control, and 'Hy-Ca' registered the greatest decrease. Root length, root area and root volume increased yet root diameter decreased correspondingly with calcium concentration ascending under hypoxia. High concentration of calcium did not take a positive effect on shoot dry weight, even an inhibition to shoot dry weight compared with single hypoxia stress in 'Lvbachun No.4'.Under short-term hypoxia stress, Pn, Gs, Ci and Tr in two cultivars of cucumber...