Studies On Physiological Mechanism Of Sugar Accumulation In Parthenocarpy Of Cucumer(Cucumer Sativus L.) Fruit

To research the effects of spermidine on parthenocarpy of cucumber five different ability of parthenocarpy of cucumber were treated with spermidine. Differences of sugar contents and activities of sucrose-metabolizing enzymes and the relationship between them were studied when spermidine or not along with non-pollination was applied to parthenocarpic and non-parthenocarpic lines (EP-6 and ZR-2, respectively) of cucumber. The effects of exogenous treatment with spermidine (spd) and polyamine biosynthetical inhibitor- MGBG, using ¹⁴C-labeling method, on the partitioning of assimilates and the relationship between that and parthenocarpy and fruit development of cucumber were investigated. The main results were as follows:1. The marked effects of spermidine on parthenocarpy of diferent cucumber cultivars were found. Generally available concentration for parthenocarpy and development of cucumber fruits was 0.25-1mmol/L of spermidine.2. The close relationship between fructose content and the ability of parthenocarpy of cucumber was found, and the fruits from parthenocarpic line EP-6 had higher fructose content. Spermidine treatment resulted in increasing of frutose content and then parthenocarpy for non-parthenocarpic line ZR-2.It implied that parthenocarpy of cucumber was promoted by regulating the accumulation of fructose content in fruit of ZR-2. Lower content of invertases in early stages of parthenocarpic furit may be one reason of parthenocarpy. Sucrose synthase activity of EP-6 fruit was higher than that of ZR-2 and such difference might be one of main reason resulting in cucumber parthenocarpy. Not marked effects of spermidine on activity of sucrose synthase of non-parthenocarpic line ZR-2 were found.3. The assimilate export of cucumber was enhanced by exogenous application of spd and resulted in parthenocarpy and fruit development. And the assimilate export of cucumber was restrained by exogenous application of MGBG and resulted in non-parthenocarpy.4. More assimilates ¹⁴C-labeled were partitioned into parthenocarpic fruits. It implied that sink activity of non-parthenocarpic line ZR-2 be regulated actively by spd. Mesocarp of cucumber fruit possessed mighty ability of striving for assimilates and much more sucrose and fructose accumulation was found in the flesh of cucumber.5. It is concluded that cucumber parthenocarpy caused whether by spd or not is related to the efficient partitioning of assimilates ¹⁴C- labeled in sink (fruit), and mesocarp is the most powerful sink of accumulating for assimilates, and main forms of assimilates accumulated in mesocarp are both sucrose and fructose.