The Mechanism Of Parthenocarpy In Watermelon Based On The Soft X-Ray Irradiation

Watermelon is one of the favorite fruits,which is widely cultivated in the world.Seedless watermelon is somehow popolar for its convenient to eat.At present,triploid watermelon,hybrided from tetraploid watermelon and diploid watermelon,is the main source of seedless watermelon.However,the breeding and hybridization process are complex,time-and labour-consuming.In this study,soft-x radiated pollen was induced to produce parthenocarpy watermelon,as well as used for further study on the mechanism of parthenocarpy in watermelon.The main results are as follows:1.Radiated watermelon pollen with soft-x radiation can lead to watermelon parthenocarpyPollination with radiated pollen can induce the expansion of watermelon ovary and develop into the mature fruit.There are no significant differences in size between normal seeded watermelon fruit and the parthenocarpy fruit.The unpollinated watermelon fruit cannot spontaneously expand and develop to mature fruit.2.Auxin,cytokinin play an important role in the development of watermelon parthenocarpic fruit.In this study,the content of hormones was detected by liquid chromatography-tandem mass spectrometry(LC-MS)in unpollination,normal seeded watermelon fruit and parthenocarpy watermelon fruits induced by radiated pollen.The IAA,cytokinin IP(isopentenyladenine)and ZR(trans-zeatin)increased significantly in the early part of the watermelon fruit,but began to decline at 6-9 days.Normal seeded fruit and parthenocarpy fruit had a significant higher content of GA4 since the first day after the pollination,compared with the un-pollinated fruit.In contrast,the endogenous contents of auxin and cytokinin in unpollinated watermelon fruit were kept in low level,which indicates that auxin,gibberellin,cytokinin participate in the development of watermelon parthenocarpy.The relative expression of CIYUCCA4 and CIYUCCA6 in the first day of normal and parthenocarpy fruit were about 8-9 times higher than the flowering day.Besides,the expression of the gene involved in the gibberellin and cytokinin biosynthesis increseas dramatically.Appllication of exogenous auxins and cytokinins can induce unpollinantion watermelon fruit to expand and growth.Thus,auxins and cytokinins play an important role in the fruit of a single fruit.3.Gibberellin can regualate the fruit expand in the late stage of the fruit growth.Gibberellin is the control of the late expansion of watermelon fruitln this study,single plant hormones and plant hormone analogues were used to treat unpollination watermelon ovaries.GA3 and GA4 can not induce the watermelon to be expand.The seeded and pathenocarpic fruit treated with the Gibberellin inhibitor PCB and CCC can be inhibited to expand in the late stage of the fruit.But it makes no affect on the fruit set.under the conditions of high cytokinin concentration.this inhibition will be eliminated.so thegibberellin isn't key role in control of the parthenocarpic fruit set and growth.But the gibberellin can regualate the fruit expansion in the late stage of the fruit growth.