红树植物秋茄类黄酮代谢及其抗氧化活性对高盐胁迫的响应

以红树植物秋茄为试验材料,设置不同浓度NaCl(0、200和500mmol·L-1)处理的砂培实验,应用qRTPCR分析秋茄叶片中类黄酮物质合成上游的4个关键酶基因——苯丙氨酸解氨酶基因(PAL)、肉桂酸羟化酶基因(C4 H)、4-香豆酰辅酶A连接酶基因(4CL)和查尔酮合成酶基因(CHS)的转录水平,并对关键酶活性进行了分析,同时测定了幼苗生物量、钾钠离子含量、类黄酮含量及其抗氧化活性,以探讨秋茄耐盐性与类黄酮物质的关系,为揭示木本植物耐盐机制奠定基础。结果显示:(1)在盐处理条件下,秋茄叶片中PAL、4CL、C4 H和CHS4个关键酶基因的转录水平显著上调,PAL、4CL、C4H酶活性和CHS含量随着盐浓度的增加而明显上升。(2)与对照相比,秋茄根、茎、叶干重在盐处理3d和15d后均无显著变化,而秋茄株高仅在200mmol·L-1盐处理15d后显著增加,其余浓度和时间均未发现有显著性变化。(3)随着盐浓度的升高,秋茄叶片类黄酮含量显著增加,K+/Na+明显下降,丙二醛含量显著降低,活性氧自由基清除率显著增加。研究表明,盐处理加强了秋茄叶片中类黄酮代谢过程中相关酶基因的表达,类黄酮物质的累积有助于其抗氧化能力的提高,进而提高秋茄的抗盐性,维持盐胁迫下秋茄的正常生长。

Flavonoid Metabolism and Antioxidant Activity in Response to Salt Stress in Mangrove Kandelia candel

In the present study, mangrove Kandelia candel (L.) Druce were potted in sand and treated with different NaCl concentrations (0, 200 and 500 mmol·L^-1).The relative expression of four key genes in the flavonoid metabolism, phenylalanine ammonia lyase (PAL), cinnamic acid hydroxylase (C4H), 4 p coumaric acyl coenzyme A ligase (4CL) and chalcone synthase(CHS) were analyzed in response to salt stress by quantificational Real time Polymerase Chain Reaction (qRT PCR). In addition, the biomass, K⁺ and Na⁺ contents, the activities of key enzymes, the contents of flavonoid and the antioxidant activity in response to salt of K. candel were investigated. Our results showed that: (1) the expression levels of PAL, 4CL, C4H and CHS were up regulated significantly under salt conditions; the activities of PAL, 4CL and C4H as well as CHS content were increased significantly with salt concentration increasing; compared with the control. (2) The plant height as well as the dry weight of leaf, root and stem were not changed significantly in NaCl treatment for 3 d and 15 d except the plant height significantly changed in 200 mmol·L^-1 NaCl treatment for 15 d. (3) The content of flavonoid, and the scavenging rate of hydroxyl radical and superoxide free radical were increased, the K⁺/Na⁺ ratio and the content of MDA were decreased significantly. These results indicate that the flavonoid metabolism in K. candel under salt conditions can be enhanced and may play an important role in the adaption to the saline environment. Accumulation of flavonoids contributes to oxidation resistance and salt tolerance of K. candel in order to maintain plant growth under salt conditions.