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Abstract
Through investigating the physiological and molecular changes induced by 24-epibrassinolide (EB) during the germination process, it was observed that the trend of results obtained was concentration- dependent. On the bases of the results obtained, it was found that the relatively low applied concentration of EB (0.5 μM) enhanced the events pre-requiset for successful germination of Cucurbita pepo L. (C.pepo) seeds. The reverse was true in case of applying the relatively high concentration (10 μM). A relatively high concentration of EB was required for priming C. pepo seeds. The significant increase induced by this treatment in the activity level of catalase, peroxidase and superoxide dismutase and the appearance of unique DNA fragments might be involved in enhancing seed performance as these enzymes could reverse the detrimental effects of seed deterioration that occur during the period of seed dessication and decrease the rate of lipid peroxidation which takes place upon seed germination. The rate of leakage of sugars during C.pepo seed germination was lowered by the relatively low applied concentration; meanwhile it was significantly increased in case of the relatively high concentration. The trend of EB in the bioassays sensitive to traditional hormones was mainly concentration–dependent. The efficiency of EB when applied to C.pepo grown under field conditions and cultivated in the specific season (March) and in non-specific season (June) was more pronounced on applying it to C.pepo plants that grown under the stress of hot summer. In both cases, EB enhanced vegetative growth, number of total flowers, number of female flowers, number of fruits and decreased rate of infestation with Sphaerotheca sp. which cause wilting of shoot system and induce fruit rot. Moreover, the period of the vegetative growth and productivity of EB-treated C. pepo was lengthened for more than mounth, compared with the control.