Ultracytochemical Localization and Effects of Calcium on Isoenzyme in the Leaves of Cucumis melo L. Under the Stress of Powdery Mildew

2012 
【Objective】The aim of this experiment is to study the uhracytochemical localization of calcium in mesophyll cells of Cucumis melo L.before and after inoculating Podosphaera xanthii and the effects of exogenous calcium on three isoenzymes of defense enzymes which will be useful for further elucidating the process of calcium signal transduction and resistance mechanism to powdery mildew of melon.【Method】With the method of electron microscope and cytochemistry technology,a hydroponic experiment was carried out to explore the effects of different calcium treatments on isoenzymes of peroxidase(POD),catalase(CAT) and superoxide dismutase(SOD) in leaves of the melon seedlings under powdery mildew stress.【Result】The calcium in mesophyll cells of resistant variety ‘MR-1’ and in susceptible variety ‘JS’ gathered in cytoplasm and there were a remarkable increase of calcium level in cytoplasm and reduced greatly in vacuolate and intercellular space when inoculating P.xanthii for 2 d.The calcium localization in leaf cells of ‘MR-1’ trended to the status as before inoculating when the seedlings were treated for 6 d.However,larger calcium deposited and localized together in the cytoplasm of ‘JS’ and the structure of mesophyll cells were destroyed until to death and there were no recover of calcium from cytoplasm into vacuolate and intercellular space.Compared with the control,the application 6 mmol.L-1CaCl2in nutrient solution significantly alleviated the stress on the melon leaves system that the activities of SOD,POD and CAT isoenzymes were significantly improved,while application of 75 mmol.L-1 LaCl3 in nutrient solution significantly inhibited the three isoenzymes activities.【Conclusion】Calcium ditribution in leaf cells of C.melo L.changed greatly due to its resistance ability at the stress of powdery mildew.A lot of Ca2+was released from Ca2+pool(vacuoles) into cytoplasm,then was pumped return vacuoles in mesophyll cells of resistance variety ‘MR-1’,but in mesophyll cells of susceptible variety ‘JS’,there only occurred the first stage.Exogenous calcium probably increased calcium transport to the plant,improved the signal transmission to the body,and enhanced the scavenging of reactive oxygen species in plant cell under stress.Thereby,exogenous calcium enhanced the ability of powdery mildew resistance of melon plants.
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