油菜素内酯对盐胁迫下香樟叶片光合色素以及叶绿素荧光的影响

Effects of exogenous 24-epibrassinolide on chlorophyll content and chlorophyll fluorescence characteristics of camphor seedlings under salt stress

为了揭示油菜素内酯(24-epibrassinolide,EBR)对香樟耐盐性的影响,以香樟为试验材料,设置在100mmol/L的单一盐浓度下,施加不同质量浓度EBR(0.1、0.2、0.3、0.4、0.5mg/L),以清水为对照,分别观测在盐胁迫下不同质量浓度EBR沾根处理对香樟形态指标、光合色素和叶绿素荧光特性的影响。结果表明:1)EBR处理可以不同程度地提高盐胁迫下香樟幼苗植株相对含水率,增加其比叶面积、干鲜比以及叶肉质化程度,降低盐害指数,并在EBR质量浓度为0.3mg/L时达到最大值;2)盐胁迫后,叶片叶绿素a(chlorophyll a,Chla)、叶绿素b(chlorophyll b,Chlb)含量明显低于对照,外施EBR可以提高香樟的叶绿素的含量;3)质量浓度为0.3 mg/L的EBR缓解盐胁迫对PSⅡ反应中心破坏的效果最好,显著提高100 mmol/L盐胁迫下香樟幼苗叶片的最大荧光(maximal fluorescence,Fm)、PSⅡ最大潜在光化学效率(optimal/maximal PSⅡefficiency,Fv/Fm)、PSⅡ潜在活性(potential activity of PSⅡ,Fv/Fo)、PSⅡ实际光化学效率(actual photochemical efficiency,ФPSⅡ),降低初始荧光(minimal fluorescence,Fo)及非化学淬灭系数(pon-photochemical quenching,NPQ);4)盐害指数(salt injury index,SI)、水分饱和亏缺(water saturation deficit,WSD)、叶绿素含量(chlorophyll,Chl)、比叶质量(specific leaf mass,SLM)两两呈正相关,与叶肉质化程度(leaf succulence,LSE)、干鲜比(dry mass/fresh mass,md/mf)呈负相关;Fm、Fv/Fm、Fv/Fo、ΦPSⅡ两两呈正相关,与NPQ、Fo、Chl呈负相关。

In China,vast areas have faced the problem of soil salinization.To ameliorate this phenomenon,researchers found that it is useful by increasing the salinity tolerance of plants and strengthening the study of plant salt-resistance and the mechanisms of salinity tolerance.Cinnamomum camphora is a king of excellent evergreen tree,street tree and overshadow tree,however,it un-favorites in dry,barren and saline-alkali soil.Besides,soilsalinity requires less than 0.2%.In Jiangsu Province,soil pH is on the high side.It is difficult to meet the normal growth needs of camphor plants because of the deficiency of organic matter, which seriously affects the introduction,use and reproduction of C.camphora.Therefore,it is of significance to study the mechanism of salinity tolerance.In order to reveal the effects of EBR on the salt tolerance of C.camphora,with camphor as experiment materials,we set the steadfast salt concentration at 100 mmol/L,applied different concentrations of EBR（0.1,0.2,0.3,0.4,0.5mg/L）with the control by only using water,and observed the influence of EBR-stick treatment on camphor root morphological indexes,photosynthetic pigments and chlorophyll fluorescence parameters.The results showed that：compared with the control group,at a specific salt stress,the salt injury index（SI）of camphor seedlings increased,as well as the water saturation deficit（WSD）;meanwhile,the leaf relative water content,the specific leaf area,fresh and dry ratio（md/mf）,decreased to some extent and leaf succulence（LSE）also showed a significant decline.EBR treatment with different concentrations could significantly improve the relative moisture content specific leaf areas,fresh and dry ratio and leaf succulence of camphor seedlings;reduce SI,and reached the maximum when the EBR concentration was 0.3mg/L.After suffering salt stress,the contents of chlorophyll a and chlorophyll b were significantly lower than that of the control groups,reducing 65.33% and 45.87%,respectively.The external application of EBR with different concentrations can significantly increase the content of chlorophyll of C.camphora;Chlb（chlorophyll b）,Car and Chla（chlorophyll a）showed a similar variation tendency,and reached the maximum when the EBR concentration was 0.3mg/L.0.3mg/L EBR was the best choice that could alleviate the destructive effect of salt stress on PSⅡ reaction centers.It significantly improved the Fm（maximal fluorescence）,Fv/Fm（optimal/maximal photochemical efficiency of PSⅡin the dark）,Fv/Fo（potential activity of PSⅡ）,ФPSⅡ（potential photochemical efficiency of PSⅡ）of camphor seedling leaves and reduced Fo（minimal fluorescence）and NPQ（non-photochemical quenching）under 100mmol/L salt stress.There were significant positive correlations among SI,WSD,Chl,specific leaf mass,and the significant negative correlations were observed with LSE,md/mf.Therein,the three groups with larger correlation were：SI and water saturation deficit,water saturation deficit and chlorophyll content,leaf succulence and fresh and dry ratio.Fm,Fv/Fm,Fv/Fo,ΦPSⅡ had positive correlation with each other while had negative correlation with NPQ,Fo,Chl.Therein,the three groups with larger correlation were：Fm and Fv/Fo,Fv/Fo andΦPSⅡ,NQP and ΦPSⅡ.