| Ca2+ and ethylene are essential to the plant, and they regulated many physiological/biochemical activities together in plant, especially for the ripening and senescence of fruit and vegetable. As a result, the relationship between Ca2+ and ethylene was focused by postharvest researchers. The intact fruit, pericarp discs and etiolated seedling of tomato were used as material, and the method of culturing iomaio pericarp in vitro was taken in the paper, to carried out the experiments on the followings: the effect of Ca2+ on ethylene biosynthesis and signal transduction, the role that ABA and CaM played in regulation of ethylene biosynthesis by calcium, the relationship between Ca2+ and polygalacturonase(PG), lipoxgenase(LOX), expansin(EXP) during fruit softening, the effect of calcium on expression of LEACO1 LEACS1A NR LEERF2 in tomato etiolated seedling. All these aimed to elucidate the role of calcium in regulation of ethylene biosynthesis and signal transduction and the effect of calcium on fruit softening.In both wild type and never ripe tomato pericarp discs, the effect of calcium on ethylene production, intermediate metablits and key enzymes in ethylene biosynthesis were similar, whichindicated that the regulation mechanism of calcium on ethylene biosynthesis was the same in bothmaterials and the effect of calcium on ethylene biosynthesis was independent of ethyleneperception in mature green tomato fruit.In wild type tomato pericarp discs, ethylene production, electrolytes leakage and MDA content decreased with calcium treatment, and ACC content increased. However, calcium treatment had little effect on the ACS activity and expression of LEACS2, the limited-step enzyme in ethylene biosynthesis pathway. All these indicated calcium could inhibite ACO accessbility to ACC by decreasing membrane permeability. Electro-microscopic cytochemistrical results showed that the deposits of calcium antimonate located in cell wall and membrane of discs treated with calcium were higher than that of control. The application of exogenous ACC to tomato pericarp discs was carried out to testified whether calcium could prevented ACC to cytoplasm by decreasing membrane permeability and the results showed that the ethylene production increased rapidly and that difference between the control and calcium treatment is not significant(P<0.05), which indicated ACC is prevented to cytoplasm by calcium through cell membrane, ACC was inhibited accessibility to ACO and ethylene production decreased. In addition, it is suggested that LEAC01 expression was inhibited by calcium, which also inhibited ethylene production.In order to investigate the role that ABA play in regulation of ethylene biosynthesis by calcium, the wild type, ethylene receptor mutant(iVr) and ethylene biosynthesis defective(antisense ACS) tomato pericarp discs at mature green stage were treated with 1 mmol.L-1 ABA and 50 u mol. L-1 Fluridone(ABA biosynthesis inhibitor). In addition, the exogenous ABA content was measured in wild type and never ripe tomato pericarp discs treated with different calcium. The results suggested that ABA was involved in the regulation mechanism of ethylene biosynthesis by calcium and ABA could regulated ethylene biosynthesis through ethylene signal transduction pathway.CaM inhibitor(W5,W7) decreased the inhibition effect of calcium on ethylene production and LEACO1 expression in wild type tomato pericarp discs excised from mature green tomato fruit, but CaM inhibitor has little effect on LEACS2 expression. These indicated calcium depended on CaM to prevent LEACO1 expression and regulate ethylene biosynthesis.In order to investigated the relationship between calcium and PG/LOX/EXP, wild type and never ripe tomato pericarp discs at mature green stage were treated with different calcium. It was indicated that the activity of LOX and expression of LELOXB were inhibited by CaCl2 treatment in wild type tomato pericarp discs, but calcium had no effect on LOX activity and LELOXB expression in never-ripe tomato pericar... |
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