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为了探讨内源水杨酸(salicylic acid,SA)在黄瓜幼苗光合系统响应低温胁迫中的作用机制,采用高效液相色谱法测定低温下黄瓜叶片中内源SA含量的变化;通过SA合成抑制剂Paclobutrazo(lPac,100μmol·L-1)喷施和外源SA(50μmol·L-1)饲喂的方法调节内源SA含量,并测定不同处理幼苗的叶绿素荧光参数和光合碳同化关键酶基因的转录水平。结果显示:低温引起黄瓜幼苗内源SA含量升高,Pac预处理抑制SA的积累。低温导致PSⅡ的最大光化学效率(Fv/Fm)、实际光化学效率(ΦPSⅡ)、潜在光化学活性(Fv/Fo)和光合电子传递效率(ETR)等降低,叶片光化学猝灭参数[(Y(NO)]升高;内源SA含量降低使PSⅡ活性下降幅度增大,加重了叶片的光损伤程度。低温下PSⅡ吸收的光能分配于光反应的部分减少,而以非光化学反应的过剩能量耗散Ex为主要的光能分配途径,内源SA含量降低会加剧光能向Ex的分配。低温时喷施Pac的幼苗中Rubisco小亚基基因(RbcS)和碳酸酐酶基因(CA)的表达水平显著低于对照植株。对喷施Pac的幼苗外源饲喂SA后,内源SA含量升高,低温下叶片光合活性得到有效恢复,光损伤降低,光能分配趋于合理,RbcS和CA的表达水平升高。上述结果表明,低温下内源SA的积累有助于维持黄瓜叶片中较高的光系统活性和碳同化能力,从而保护光合系统,降低低温胁迫对植物的损伤。
In order to investigate the mechanism of endogenous salicylic acid (SA) in response to low temperature stress in cucumber seedling photosynthetic system, the change of endogenous SA content in cucumber leaves at low temperature was determined by high performance liquid chromatography (HPLC) Paclobutrazol (100 mg · L -1) and exogenous SA (50 μmol·L -1) were used to regulate the content of endogenous SA, and the chlorophyll fluorescence parameters and photosynthetic carbon assimilation key enzyme genes Transcriptional level. The results showed that low temperature caused the increase of endogenous SA content in cucumber seedling and Pac pretreatment inhibited the accumulation of SA. Under low temperature, the maximum photochemical efficiency (Fv / Fm), actual photochemical efficiency (ΦPSⅡ), latent photochemical activity (Fv / Fo) and photosynthetic electron transfer efficiency (ETR) ] Increased.The decrease of endogenous SA content increased the decrease of PSⅡ activity and aggravated the degree of photodamage of leaves.The fraction of light energy absorbed by PSⅡ absorbed by photoperiod decreased at low temperature and the excess energy dissipated by non photochemical reaction Ex as the main pathway of light energy distribution, the decrease of endogenous SA content will exacerbate the distribution of light energy to Ex. The expression of Rubisco small subunit gene (RbcS) and carbonic anhydrase gene (CA) Was significantly lower than that of the control plants.After exogenous feeding of SA to the seedlings of Pac, the content of endogenous SA increased, the photosynthetic activity of leaves was effectively recovered under low temperature, the light damage was reduced and the light energy distribution tended to be reasonable. The RbcS and CA The above results indicated that the accumulation of endogenous SA at low temperature could help to maintain higher photosystem activity and carbon assimilation ability in cucumber leaves, thus protecting the photosynthetic system and reducing plant damage caused by low temperature stress.