The Mechanism Of Microencapsulated Tebuconazole’s Effect On Resistence Of Maize To Chilling Stress

Tebuconazole is a triazole fungicide, which is widely used for maize seed-coating. However, phytotoxicity and serious economic loss caused by tebuconazole may occur under chilling stress. Previous studies have found that microencapsulation of seed-coating tebuconazole can improve security of application at room temperature. In order to evaluate the security and study the biological mechanism of microencapsulated tebuconazole coated on maize seeds under chilling stress, different doses of microencapsulated tebuconazole were coated on maize seeds and its effects on maize seeds germination, maize seedlings growth, as well as gibberellin content were studied, comparing with that of nonmicroencapsulated tebuconazole. Based on these results, we viewed from genes of gibberellin metabolic enzymes, and carried out their relative expression levels under different doses of microencapsulated tebuconazole. Furthermore, we analyzed the relevant enzymes activity. Conclusions are as follows:Under chilling stress, germination rate, shoot length, fresh weight, photosynthetic pingment contents, respiratory rate and gibberellin content of maize seedlings showed downward trends with increasing dose of nonmicroencapsulated tebuconazole. At dose range of 0.06 ~ 0.6 g a.i./kg, these indexes were lower in nonmicroencapsulated tebuconazole treatments than that of microencapsulated tebuconazole treatments. At rate of 0.6 g a.i./kg, under microencapsulated tebuconazole treatments germination rate, shoot length and fresh weight were respectively enhanced by 48.28%, 55.59% and 71.43% relative to nonmicroencapsulated tebuconazole. Besides, chlorophyll content, carotenoid content, respiratory rate and gibberellin content under microencapsulated tebuconazole treatments were respectively 2.16, 1.14, 1.89 and 1.95 times of that under nonmicroencapsulated tebuconazole treatments at dose of 0.6 g a.i./kg. Our findings suggested that by comparison to nonmicroencapsulated tebuconazole, microencapsulation of tebuconazole can enhance security of use under chilling stress.Genes’ relative expression levels were carried out by real-time q PCR. The results showed under chilling stress the relative expression levels of gibberellin synthetic enzymes KO and GA3 ox related genes were gradually suppressed as the rate of nonmicroencapsulated tebuconazole increased, and they were lower than that of microencapsulated tebuconazole treatments at the same doses of tebuconazole. At dose of 0.6 g a.i./kg, relative expression levels of Zm KO1, Zm KO2, Zm GA3ox1 and Zm GA3ox2 under microencapsulated tebuconazole treatments were 2.98, 1.88, 3.3 and 2.05 times of that under nonmicroencapsulated tebuconazole treatments, respectively. Whereas, with excepetion of Zm GA2ox10, the relative expression levels of gibberellin catabolic enzyme(GA2ox) related genes showed upward trends with the increasing rate of nonmicroencapsulated tebuconazole, which were higher than that of microencapsulated tebuconazole treatments at the same dose of tebuconazole. Among these catabolic enzyme related genes, there were great difference between relative expression levels of Zm GA2ox1 Zm GA2ox4 and Zm GA2ox7 under the two tebuconazole formulations treatments. At rate of 0.6 g a.i./kg, the three genes’ expression levels under microencapsulation treatments were 0.48, 0.32 and 0.2 times of that under nonmicroencapsulated tebuconazole treatments.The results of ELISA determination revealed under chilling stress compared with control treatments, activities of gibberellin synthetic enzymes(KO and GA3ox) were decreased, while the activity of gibberellin catabolic enzyme(GA2ox) was improved under nonmicroencapsulated tebuconazole treatments. However, at the same dose of tebuconazole, activities of KO and GA3 ox were higher and activities of GA2 ox was lower in microencapsulated tebuconazole treated plants than that of nonmicroencapsulated tebuconazole treatments. At rate of 0.6 g a.i./kg, activities of KO, GA3 ox and GA2 ox in microencapsulated tebuconazole treated plants were 2.25, 1.69 and 0.74 times of that under nonmicroencapsulated tebuconazole treatments.In conclusion, compared with nonmicroencapsulated tebuconazole treatments, microencapsulation of tebuconazole can enhance chilling stress resistence of maize. The safety mechanism of microencapsulated tebuconazole was that it can promote gibberellin synthetic enzymes related genes’ expression and inhibit catabolic enzyme related genes’ expression, thus changing activities of relevant metabolic enzymes, which was benifical for generation and accumulation of gibberellin in maize. The results further clarify that microencapsulation is an effective way to overcome negative effects of seed-coating tebuconazole under chilling stress. The results will present a method for safe application of triazole fungicides, and provide theoretical guidance for eliminating detrimental effects of other crops under chilling stress.