油菜素内酯对盐胁迫刺槐苗光合作用及叶绿体超微结构的影响

摘要

[目的]采用蘸根方式外源添加不同质量浓度油菜素内酯(BRs)处理刺槐幼苗,研究刺槐苗在盐胁迫条件下生长、光合及叶绿体结构的变化,为盐碱地造林提供技术指导.[方法]以1年生刺槐苗为研究对象,用不同质量浓度(0.1,0.3,0.5 mg/L)BRs对苗木进行蘸根处理,然后经100 mmol/L NaC1胁迫处理50 d后,以未添加BRs和未进行盐胁迫处理的刺槐苗为空白对照(CK1),以未添加BRs只进行盐胁迫处理的刺槐苗为胁迫对照(CK2),观测分析苗木的形态和水分生理指标、光合色素、基础光合参数和叶绿体超显微结构的变化.[结果]与CK1相比,CK2的苗高/基径和叶片相对含水量显著(P＜0.05)降低,比叶重显著(P＜0.05)增加,盐害指数显著(P＜0.05)上升;叶片叶绿素a、叶绿素b含量显著(P＜0.05)下降,叶绿素a/b有所上升;叶片的光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、胞间CO2浓度(Ci)、瞬时水分利用效率(WUE)均有所下降,气孔限制值(Ls)上升;叶片叶绿体超显微结构遭到破坏,叶绿体排列松散,形态肿大,嗜锇颗粒减少,类囊体片层松散,叶片光合作用受到抑制.与CK2相比,外源添加BRs的各处理苗高/基径增大,除0.1 mg/L BRs处理外其他处理的比叶重均有所下降,叶片相对含水量上升,盐害指数显著(P＜0.05)降低;叶绿素a、叶绿素b含量和叶绿素a/b上升;刺槐叶片Pn提高,0.5 mg/L BRs处理可以增加盐胁迫刺槐苗叶片的Gs,并维持一定的Tr、Ci和WUE;通过观察叶片叶绿体结构,发现0.5 mg/L BRs处理能够使盐胁迫刺槐苗维持一定的叶绿体数,保持叶绿体结构的完整和类囊体片层的紧密度,增加嗜锇颗粒数目,维持叶绿体基本功能.[结论]盐胁迫刺槐幼苗的光合作用受到抑制,而BRs蘸根处理能够使刺槐幼苗在盐胁迫下维持一定的光合作用,提高苗木的耐盐性,其中以0.5 mg/L BRs处理效果较好.%[Objective] This article focus on the effect of the exogenous 24-epibrassinosteroid (BRs),used by roots dipping way,on photosynthesis and ultrastructure of chloroplasts in Robinia pseudoacacia seedling sunder salt stress which results could provide the technical guidance for forestation on saline and alkaline land.[Method] The research was based on the annual R.pseudoacacia seedings used different concentration gradients of BRs(0.1,0.3,0.5 mg/L) by the root treatment under 100 mmol/L NaCl stress for 50 d.CK1 is blank control (0 mmol/L NaCl+0 mg/L BRs),CK2 is stress control (100 mmol/L NaCl+0 mg/L BRs).According to the analysis of multiple comparison and ANOVA((P＜0.05)),it showed some results about the changes of morphological,moisture physilological indexed,chlorophyll,photosynthetic and chloroplast ultrastructure parameters.[Result] We found that the salt stress had a significant reduction of plant height/diameter (H/SBD) and relative water content(RWC)(P＜0.05) of the leaves,a notable increase with specific leaf weight(SLW) and salt injury index(P＜0.05).The chlorophyll a and chlorophyll b also declined significantly(P＜0.05),but the chlorophyll a/b rose slightly under salt stress.The leaf photosynthetic rate (Pn),stomatal conductance (Gs),transpiration rate (Tr),intercellular CO2 concentration (Ci),water use efficiency(WUE)decreased and the chloroplast ultrastructures in the leaves of R.pseudoacacia seedings were damaged by the salinity (100 mmol/L NaC1).Through the usage of exogenous BRs,the results showed that in contrast to CK2,application of BRs improved the values of H/SBD and RWC,SLW decreased besides 0.1 mg/L BRs treatment and the salt injury index had an obvious reduce (P＜0.05).The effective role of BRs played in maintaining the normal photosynthesis of the leaves under salt stress attributed to improvement with the contents of chlorophyll a,chlorophyll b and chlorophyll a/b.As well as,the concentration of 0.5 mg/L BRs increased stomatal conductance (Gs),maintained the transpiration rate (Tr) and intercellular CO2 concentration (Ci),water use efficiency(WUE),kept leaf photosynthesis compared to stress control(CK2).Analysis of ultrastructure of chloroplasts,the plants dealing with BRs can keep the certain numbers of chloroplasts,maintain the structure of chloroplasts completely and tightness of thylakoid lamellas,increase the numbers of eosinophilic osmium particles into leaves,which were advantage for photosynthesis by maintaining the functionality of chloroplasts.[Conclusion]These results suggest that the photosynthesis of the seedings (Robinia L.)is restrained under 100 mmol/L salt stress for 50 d,adding BRs is able to maintain the certain degree of leaf photosynthesis,improves the tolerance of the R.pseudoacacia seedings under the stress (100 mmol/L NaC1) and the optimal concentration of BRs is 0.5 mg/L.