外源硫对镉胁迫下马齿苋光合性状和矿质元素吸收的影响

从光合反应系统揭示外源硫(S)诱导马齿苋镉(Cd)耐受性的生理机制,为外源S缓解重金属毒害提供理论依据.采用营养液培养,研究外源S供体(NH4)2SO4对100 mg/L Cd胁迫下马齿苋叶片光合色素、光合特性、叶绿素荧光参数和矿质营养元素的影响.结果表明,Cd胁迫可显著降低马齿苋叶片中叶绿素a和叶绿素b含量;净光合速率、蒸腾速率、气孔导度均显著降低,而胞间二氧化碳浓度上升,表明非气孔因素是Cd胁迫诱导马齿苋光合抑制的主要因素;同时,PSⅡ实际光化学效率(ФPSII)、电子传递效率(J)、化学猝灭系数(qP)显著下降,而非化学猝灭系数(qN)显著上升,表明Cd胁迫影响马齿苋PSⅡ反应系统的正常运行.外施400 mg/L(NH4)2SO4显著提高马齿苋叶片叶绿素a含量、叶绿素b含量和叶绿素a/b比值,增强马齿苋叶片光合作用和PSⅡ原初光化学反应量子效率.对5种与光反应系统密切相关的矿质元素含量进行分析发现,Cd处理显著增加马齿苋叶片中的Ca和Fe含量,显著抑制马齿苋对Mg、Mn和Cu的吸收.Cd胁迫下马齿苋叶片的变黄与Mg、Mn的亏缺有关,而与Fe缺乏无关;添加外源S可显著提升马齿苋叶片中Ca、Mg、Fe、Cu和Mn含量,从而增强Cd胁迫下马齿苋叶片的PSII反应系统功能.

Effects of Exogenous Sulfur on Photosynthetic Characteristics and Mineral Elements Absorption in Portulaca oleracea Under Cadmium Stress

Uncovering the physiological mechanism of exogenous sulfur inducing cadmium(Cd)tolerance in Portulaca oleracea from the aspect of photosynthetic reaction system may provide a theoretical foundation for application of S in alleviating the toxicity of heavy metals in plants.A hydroponic experiment was conducted to investigate the effects of exogenous(NH4)2SO4,an S donor,on the photosynthetic pigments,photosynthetic characteristics,chlorophyll fluorescence parameters,and mineral element contents in P.oleracea treated with 100 mg/L CdCl2.The results showed that Cd stress resulted in the significant decrease of chlorophyll a and b,also the net photosynthesis rate transpiration rate,and stomatal conductance,while the increase of intercellular concentrations of carbon dioxide(Ci);these results indicated that nonstomatal factor was the dominant one that induced photosynthetic inhibition under Cd stress.Meanwhile,PSII actual photochemical efficiency(ФPSII),electron transfer efficiency(J),and chemical quenching coefficient(qP)all significantly decreased,whereas nonchemical quenching coefficient(qN)significantly increased;these results implied that Cd stress disturbed proper function of PSII in P.oleracea.However,the application of 400 mg/L(NH4)2SO4 significantly increased the content of chlorophyll a and b,ratio of chlorophyll a/b,meanwhile enhanced both of the photosynthesis and quantum yield of PSII photochemistry.Furthermore,Cd treatment significantly increased content of calcium(Ca)and iron(Fe),while inhibited absorption of magnesium(Mg),manganese(Mn),and copper(Cu);these results implied that the cadmium-incited etiolation of the leaves was related to the deficiency of Mg and Mn in P.oleracea,but not to Fe.In sum,adding surplus S may significantly increase the content of Ca,Mg,Fe,Cu and Mn and therefore enhance PSII system in the leaves of P.oleracea under Cd stress.