| Glucosinolates and their degradation products are not only the flavor source of Brassica vegetable, but also play an important role in lowing cancer risk and plant defense against pathogens and herbivores. As is rich in glucosinolates, model plant Arabidopsis thaliana is recognized as the best material to study the network of glucosinolate metabolism. Brassica sprouts are considered as a good system to explore metabolic regulation of glucosinolate in vegetables due to their short life cycle and easily controlled culture condition. In recent years, the biosynthetic pathway of glucosinolate in Arabidopsis has been clarified and their regulatory network is becoming the hot topic. Synthetic pathway of glucosinolate in Brassica vegetables is gradually being elucidated. Studies have shown that many biotic and abiotic factors can regulate the biosynthesis and metabolism of glucosinolate. Glucose is not only the basic energy source of plant growth and development, but also acts as a signal molecule modulating many life processes. In the present study, we carried on the research about the regulatory mechanism of glucose signal on glucosinolate biosynthesis, analysis about the effect of glucose on primary sulfur metabolism, as well as the interaction of glucose and plant hormones on regulating glucosinolate biosynthesis in Arabidopsis. Besides, function of glucose and plant hormones on glucosinolate accumulation in Brassica vegetable was discussed by using Chinese kale sprout, one Brassica vegetable with Chinese characteristics, based on previous systematic study in Arabidopsis, so as to lay the foundations for promoting quality of Brassica vegetables. The main results are as follows:1. Glucose positively regulates aliphatic and indolic glucosinolate biosynthesis. The effects of glucose on glucosinolate biosynthesis in Arabidopsis were investigated in this study by using mutants related to glucosinolate biosynthesis and regulation, as well as glucose signaling. The results showed that glucose induced MYB transcription factors that could regulate the biosynthetic genes of glucosinolate, mainly MYB28and MYB34in HXK1-depending manner, and finally enhanced the accumulation of glucosinolate. In addition, glucose induced the expression of sulfate metabolic genes and enhanced the accumulation of cysteine and glutathione, indicting that the induction of glucose on glucosinolate accumulation should mainly result from the enhanced sulfate assimilation and not the sulfur partitioning into glucosinolate biosynthesis. What’s more, glucose signal transduction response clement ABI5 affected the biosynthesis of glucosinolate, but only participated in the regulation of glucose on aliphatic glucosinolate biosynthesis, not glucose-driven induction of indolic glucosinolate accumulation. However, ABI5could interact with indolic MYBs in yeast, which indicated that ABI5might modulate indolic glucosinolate biosynthesis through interaction with indolic MYBs.2. Glucose and ABA have a synergistic effect on enhancing glucosinolate biosynthesis. The inductive effect of glucose on the content of glucosinolate was analyzed in both aba2-lmutant and wild type, results showed that the deficiency of endogenous ABA did not inhibit the induction of glucose on enhancement of glucosinolate biosynthesis, indicating that glucose-driven induction of the glucosinolate pathway is not strictly dependent on the synthesis of ABA. The exogenous ABA application was also conducted to detect the direct effect of ABA on glucosinolate biosynthesis. Data showed that ABA could induce the expression of MYBs and significantly increase glucosinolate accumulation. Moreover, ABI5, involved in the glucose-enhanced glucosinolate biosynthesis, also participated in ABA-regulated glucosinolate biosynthesis. It was worth noting that ABA inhibited the content of4MTB, which might due to acceleration of the conversion from4MTB to4MSOB (precursor of the most effective natural compound in anticancer), suggesting an important potent practical value of ABA. The increase of glucosinolate accumulation caused by treatment with both glucose and ABA is much stronger than the simply addictive of each single one, demonstrating that glucose and ABA have a synergistic effect on enhancing glucosinolate biosynthesis. Besides, the deficiency of HXK1did not disturb the enhancement of ABA on glucosinolate accumulation, confirming the regulation of ABA on glucosinolate biosynthesis is HXK1-independent, and ABA might act downstream or parallel of HXK1.3. Glucose is synergetic with JA in regulating certain glucosinolates in Chinese kale sprout. We treated Chinese kale sprout with low concentration of glucose (3%) and plant hormones (5μM JA) alone or together. The results showed that all kinds of treatments did not cause significant effect on biomass of sprouts. Treatment with glucose and JA together increased the accumulation of glucoiberin and glucoraphanin (two kinds of aliphatic glucosinolates with high anticancer activity) significantly with respect to glucose-or JA-alone treatment, and their contents were increased by63%and52%when compared with control treatment. Moreover, glucose enhanced the promotion of JA on the content of4-methoxy glucobrassicin, a kind of indolic glucosinolate, which plays important role in plant immunity. In the meanwhile, the content of total anthocyanins was significantly increased by application of glucose and JA together. Therefore, quality of Brassica sprouts could be improved by JA application together with glucose.4. Glucose and GA have a synergetic effect on promoting glucosinolates accumulation in Chinese kale sprout. Treatment with3%glucose or/and5μM GA did not affect the growth of Chinese kale sprouts significantly.5μM GA treatment had no dramatic effect on the accumulation of both aliphatic and indolic glucosinolates, compared with treatment by control. But, when GA was applied together with glucose, the content of many aliphatic glucosinolates (Progoitrin, Sinigrin, Gluconapin, Glucoerucin, Gluconapoleiferin) and indolic glucosinolate1-methoxy Glucobrassicin were boosted significantly. They were increased by43%,54%,56%,23%,43%and44%respectively with respect to control treatment. Furthermore, the total glucosinolate content in spouts was raised by44%after treatment with glucose and GA together, compared with control treatment. What’s more, treatment with glucose and GA dramatically enhanced the accumulation of total phenols and antioxidant activity. So, it could be a safe and efficient method to promote the quality of Brassica spouts through application with GA and glucose. |
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