Li Xin, Zhang Lan, Ahammed Golam Jalal, Li Zhi-Xin, Wei Ji-Peng, Shen Chen, Yan Peng, Zhang Li-Ping, Han Wen-Yan
Key Laboratory of Tea Biology and Resources Utilization, Ministry of Agriculture, Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 Meiling Road, Hangzhou, 310008, PR China.
Key Laboratory of Tea Biology and Resources Utilization, Ministry of Agriculture, Tea Research Institute, Chinese Academy of Agricultural Sciences, 9 Meiling Road, Hangzhou, 310008, PR China; Department of Horticulture, Zijingang Campus, Zhejiang University, Yuhangtang Road 866, Hangzhou, 310058, PR China.
J Plant Physiol. 2017 Jul;214:145-151. doi: 10.1016/j.jplph.2017.04.005. Epub 2017 Apr 12.
Flavonoids are one of the key secondary metabolites determining the quality of tea. Although exogenous brassinosteroid (BR), a steroidal plant hormone, can stimulate polyphenol biosynthesis in tea plants (Camellia sinensis L.), the relevance of endogenous BR in flavonoid accumulation and the underlying mechanisms remain largely unknown. Here we show that BR enhances flavonoid concentration in tea leaves by inducing an increase in the endogenous concentration of nitric oxide (NO). Notably, exogenous BR increased levels of flavonoids as well as NO in a concentration dependent manner, while suppression of BR levels by an inhibitor of BR biosynthesis, brassinazole (BRz), decreased the concentrations of both flavonoids and NO in tea leaves. Interestingly, combined treatment of BR and BRz reversed the inhibitory effect of BRz alone on the concentrations of flavonoids and NO. Likewise, exogenous NO also increased flavonoids and NO levels dose-dependently. When the NO level in tea leaves was suppressed by using a NO scavenger, 2,4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), flavonoid concentration dramatically decreased. Although individual application of 0.1μM BR increased the concentrations of flavonoids and NO, combined treatment with exogenous NO scavenger, cPTIO, reversed the effect of BR on flavonoid concentration. Furthermore, BR or sodium nitroprusside (SNP) promoted but cPTIO inhibited the transcription and activity of phenylalanine ammonia-lyase (PAL) in leaves, while combined treatment of BR with SNP or cPTIO had no additive effect. The results of this study suggest that an optimal level of endogenous NO is essential for BR-induced promotion of flavonoid biosynthesis in tea leaves. In conclusion, this study unveiled a crucial mechanism of BR-induced flavonoid biosynthesis, which might have potential implication in improving the quality of tea.
类黄酮是决定茶叶品质的关键次生代谢产物之一。尽管外源油菜素内酯（BR），一种甾醇类植物激素，能够刺激茶树（Camellia sinensis L.）中多酚的生物合成，但内源BR在类黄酮积累中的相关性及其潜在机制仍 largely 未知。在此我们表明，BR 通过诱导内源一氧化氮（NO）浓度的增加来提高茶叶中的类黄酮浓度。值得注意的是，外源BR 以浓度依赖的方式增加了类黄酮以及 NO 的水平，而 BR 生物合成抑制剂油菜素唑（BRz）抑制 BR 水平则降低了茶叶中类黄酮和 NO 的浓度。有趣的是，BR 与 BRz 的联合处理逆转了 BRz 单独对类黄酮和 NO 浓度的抑制作用。同样，外源 NO 也以剂量依赖的方式增加了类黄酮和 NO 的水平。当使用 NO 清除剂 2,4-羧基苯基-4,4,5,5-四甲基咪唑啉-1-氧基-3-氧化物（cPTIO）抑制茶叶中的 NO 水平时，类黄酮浓度显著降低。尽管单独施用 0.1μM 的 BR 增加了类黄酮和 NO 的浓度，但与外源 NO 清除剂 cPTIO 的联合处理逆转了 BR 对类黄酮浓度的影响。此外，BR 或硝普钠（SNP）促进但 cPTIO 抑制叶片中苯丙氨酸解氨酶（PAL）的转录和活性，而 BR 与 SNP 或 cPTIO 的联合处理没有相加效应。本研究结果表明，内源 NO 的最佳水平对于 BR 诱导的茶叶中类黄酮生物合成的促进至关重要。总之，本研究揭示了 BR 诱导类黄酮生物合成的关键机制，这可能对提高茶叶品质具有潜在意义。
