Tropical Biosphere Research Center, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan.
J Plant Physiol. 2012 Dec 15;169(18):1903-8. doi: 10.1016/j.jplph.2012.08.005. Epub 2012 Aug 24.
This study examined the salinity dependence of triterpenoid content and triterpenoid synthase gene expression in mangrove plants, Kandelia candel and Bruguiera gymnorrhiza (Rhizophoraceae) after long-term exposure to salinity and subsequent re-adaptation. Seedlings of the two mangrove species grown in varying salt concentrations for 4 months were divided into two treatment groups and grown for another 4 months, one group continued under the respective saline condition and the other in fresh water for re-adaptation. The total content of triterpenoids increased with increasing salinity in roots and leaves of K. candel, but only in roots in B. gymnorrhiza. This increase was reversed to a variable extent, depending on the species and organ, after transfer to fresh water. In contrast, the total content of phytosterols showed no correlation with salinity throughout the experiment. The increase in total triterpenoids was accompanied by an up-regulation of several triterpenoid synthase genes: KcMS, a multifunctional triterpenoid synthase, in roots and leaves of K. candel and BgLUS, a lupeol synthase, and BgbAS, a β-amyrin synthase, in roots of B. gymnorrhiza. The expression of root KcCAS, a cycloartenol synthase, which is involved in phytosterol biosynthesis, was not modulated by the salinity conditions but decreased with increasing salinity in leaves, followed by the restoration to the initial level after transfer to fresh water. The concentrations of individual triterpenoids, but not of phytosterols, in the roots positively correlated with the salinity. These results reinforced the importance of triterpenoids in the adaptation of mangroves to withstand salt and/or water stress.
本研究考察了红树植物秋茄（Kandelia candel）和桐花树（Bruguiera gymnorrhiza）（红树科）在长期暴露于盐度并随后重新适应后，三萜含量和三萜合酶基因表达对盐度的依赖性。在不同盐浓度下生长 4 个月的两种红树林幼苗被分为两组进行处理，再分别在各自的盐度条件下或在淡水条件下生长 4 个月进行再适应。在秋茄的根和叶中，三萜的总量随着盐度的增加而增加，但在桐花树的根中仅增加了一点。这种增加在一定程度上因物种和器官而异，在转移到淡水后会逆转。相比之下，在整个实验过程中，植物甾醇的总量与盐度没有相关性。总三萜含量的增加伴随着几种三萜合酶基因的上调：KcMS，一种多功能三萜合酶，在秋茄的根和叶中；BgLUS，一种羽扇豆醇合酶，和 BgbAS，一种β-香树脂醇合酶，在桐花树的根中。参与植物甾醇生物合成的根 KcCAS，一种环阿屯醇合酶，其表达不受盐度条件的调节，但随着叶片中盐度的增加而减少，然后在转移到淡水后恢复到初始水平。根中二萜的浓度，而不是植物甾醇的浓度，与盐度呈正相关。这些结果强调了三萜在红树植物适应盐度和/或水分胁迫中的重要性。
