乌龙茶在加工过程中特征香气物质的形成很可能是来自叶片遭受多种胁迫后的防御响应，这其中就涉及叶片叶绿体相关的上游激素信号的上调，比如茉莉酸（JA）信号。但是对于叶绿体的改变是否对叶片遭受胁迫下JA和特征香气的形成产生影响还不清楚。在茶树种质中，有一类白化诱导的黄化叶片中叶绿体的结构存在缺陷，因此刚好可以用于上述问题的探索。在本研究中，作者以‘英红9号’及其黄化突变体为材料，对正常绿色叶片和黄化叶片在遭受持续叶片损伤（乌龙茶加工过程中叶片遭受的主要胁迫）情况下二者激素及特征香气物质形成的差异进行比较分析。结果发现持续损伤条件下JA信号的一个关键转录因子基因CsMYC2显著上调表达，并且激活了正常绿色叶片和黄化叶片中JA和特征香气物质的合成；虽然叶绿体的缺陷对叶片遭受持续损伤下CsMYC2和JA合成相关基因的表达水平没有显著影响，但是却减少了持续损伤下叶片中JA的增加含量；此外，叶绿体的缺陷还减少了包括茉莉内酯和绿叶挥发物在内的挥发性脂肪酸衍生物因为响应持续损伤而增加的量。因此总体上说，叶绿体的缺陷能够影响叶片在遭受持续损伤胁迫下脂肪酸衍生型的香气代谢物的形成。

Abstract

Characteristic aroma formation in tea (Camellia sinensis) leaves during the oolong tea manufacturing process might result from the defense responses of tea leaves against these various stresses, which involves upregulation of the upstream signal phytohormones related to leaf chloroplasts, such as jasmonic acid (JA). Whether chloroplast changes affect the formation of JA and characteristic aroma compounds in tea leaves exposed to stresses is unknown. In tea germplasms, albino-induced yellow tea leaves have defects in chloroplast ultrastructure and composition. Herein, we have compared the differential responses of phytohormone and characteristic aroma compound formation in normal green and albino-induced yellow tea leaves exposed to continuous wounding stress, which is the main stress in oolong tea manufacture. In contrast to single wounding stress (from picking, as a control), continuous wounding stress can upregulate the expression of CsMYC2, a key transcription factor of JA signaling, and activate the synthesis of JA and characteristic aroma compounds in both normal tea leaves (normal chloroplasts) and albino tea leaves (chloroplast defects). Chloroplast defects had no significant effect on the expression levels of CsMYC2 and JA synthesis-related genes in response to continuous wounding stress, but reduced the increase in JA content in response to continuous wounding stress. Furthermore, chloroplast defects reduced the increase in volatile fatty acid derivatives, including jasmine lactone and green leaf volatile contents, in response to continuous wounding stress. Overall, the formation of metabolites derived from fatty acids, such as JA, jasmine lactone, and green leaf volatiles in tea leaves, in response to continuous wounding stress, was affected by chloroplast defects. This information will improve understanding of the relationship of the stress responses of JA and aroma compound formation with chloroplast changes in tea.