Study On Thinning Of5-Aminolevulinic Acid In Pear And Its Mechanism

Most fruit trees need to be thin flower and fruit in the process of production, in order to achieve the purpose of the high and stable yield of high quality. Thinning flower and fruit plays an important role in fruit production, it can prevent and reduce biennial bearing, improve the percent rate of the high quality fruit, keep the tree body haleness, extend the economic life of the fruit trees.5-aminolevulinic acid （ALA） is the first key precursor of the porphyrin compounds biosynthesis, for examper chlorophyll and heme, photosensitive element and vitamin B12. And we maked a lot of research, which found that high concentrations of ALA can be a herbicide of no toxicity and no pollution in the field, it has potential applications, broad application prospects and market prospects in agricultural production. Using green-coronal pear pollen as material, this study analyzed the effects of the ALA on thinning flower and fruit. It is found that the200kg·hm-1ALA could reduce the fruit rate in full-blossom period, And explained the mechanism of hydrophobic besides. The main results are as follows:1. Trees of pear （Pyrus sp. cv.’Dangshansuli’,’Akemizu’,’Suisho’and’Cuiguan’） were sprayed with5-aminolevulinic acid （ALA） solutions at blooming stage to study the thinning effects in Dashahe Orchard of Feng County, Xuzhou City, and Jiangpu Orchard of Nanjing City from2011to2013. The results showed that200kg·hm-1ALA applied at the full blooming stage might be suitable for pear flower thinning. Analysis showed that the superoxide dismutase （SOD） activity in the stigma treated by ALA solution was depressed, compared with the control, but the superoxidate anion production, the content of MDA increased significantly. Observation by microscopes showed that pollen germination and tube growth in the stigma of pear flowers were inhibited by ALA treatment. Thus, the peroxidation stress in stigmas and the inhibition of germination and growth in pollens might be the causes of flower abortion.2. With pear （Pyrus pyrifolia Nakai cv.’Cuiguan’） pollens as material, the effects of ALA on pollen germination in vitro and pollen tube growth were studied in the work. The results indicated that the treatment of ALA in5kg·hm-1promoted the pollen germination and pollen tube growth, but when the concentration of ALA was greater than10kg·hm-1, the pollen germination and pollen tube growth were inhibited as the increase of ALA concentrations. The inhibition of ALA on pollen germination and tube growth could be alleviated by added suitable concentrations of Ca2+, and the Ca2+effect could be eliminated by added EGTA. The measurement of Ca2+-ATPase activity in pollen tubes suggested that ALA might affect pollen germination and tube growth thrghou regulating the enzyme activity.3. Using ’Cuiguan’ pear pollen as material, the calcium ion fluorescence indicator fluo₃AM was loaded successfully into the pollen grains by low temperature loading method. Laser confocal scanning microscopy was used to study the effect of ALA on cytosolic Ca2+concentration and H2O2content in pear pollen grains. It was found that the10kg·hm-1ALA could decrease the intracellular calcium ion concentration and H2O2content. To the medium to join a certain concentration of Ca2+, the intracellular calcium ion concentration and H2O2content remains stable. It would decrease again by addition of calcium. It suggests that the inhibition of ALA on pollen germination and tube growth of pear flowers might be involved in regulation of cytosolic Ca2+concentration and H2O2content.