Na_(2)CO_(3)胁迫对赖草叶片光合、叶绿素荧光、超微结构的影响

Effect of Na_(2)CO_(3) Stress on Photosynthesis,Chlorophyll Fluorescence,and Ultrastructure of Leymus secalinus Leaves

赖草作为黄土高原乡土草,具有耐盐碱的特点。为揭示黄土高原乡土草赖草(Leymus secalinus)的抗碱能力,采用盆栽控制试验,设置8个Na_(2)CO_(3)浓度梯度(0、50、75、100、150、200、300、400 mmol/L)对赖草幼苗进行胁迫,研究Na_(2)CO_(3)胁迫对赖草幼苗的光合作用和叶绿素荧光的影响,并采用透射电镜观察叶肉细胞超微结构的变化。结果表明,随着Na_(2)CO_(3)胁迫浓度的升高,赖草幼苗的净光合速率、叶绿素含量、初始荧光(Fo)和最大荧光(Fm)呈现先升高后降低的趋势,PSⅡ最大光化学量子产量(Fv/Fm)、PSⅡ的潜在活性(Fv/Fo)逐渐降低。150 mmol/L Na_(2)CO_(3)胁迫时赖草叶片净光合速率、Fo和Fm达到最大,叶绿素含量较高;当Na_(2)CO_(3)浓度大于200 mmol/L时,赖草幼苗叶片叶绿素含量、净光合速率和Fo下降显著。透射电镜观察结果显示,50 mmol/L Na_(2)CO_(3)胁迫下,叶绿体外膜清晰,基粒片层扭曲;150 mmol/L Na_(2)CO_(3)胁迫下,叶绿体的内外膜有解体迹象,线粒体膜有破损趋势,但结构完整;400 mmol/L胁迫下,叶绿体、线粒体内外膜解体,细胞结构严重受损。赖草对150 mmol/L以下的Na_(2)CO_(3)胁迫表现出一定的适应性,叶片结构未受损伤。

As the native grass in loess Plateau,Leymus secalinus has the characteristics of salt-alkali tolerance.To reveal the alkali resistance of native grass(Leymus secalinus)in the Loess Plateau,in this experiment,a pot-control test was used,the seedlings were stressed by eight Na_(2)CO_(3)concentration gradients(0,50,75,100,150,200,300,and 400 mmol/L)to investigate the effect of Na_(2)CO_(3)stress on photosynthesis and chlorophyll fluorescence in Leymus secalinus seedlings,transmission electron microscopy was also used to observe the ultrastructural changes in mesophyll cells.The results showed that,with the increasing stress concentration of Na_(2)CO_(3),the net photosynthetic rate(Pn),chlorophyll content,Fo and Fm showed a trend of first increase and then decrease,Fv/Fm,and Fv/Fo were gradually decreased.The net photosynthetic rate,Fo and Fm reached the maximum with high chlorophyll content at 150 mmol/L of Na_(2)CO_(3)stress.Leaf chlorophyll content,net photosynthetic rate,and Fo decreased significantly at the Na_(2)CO_(3)concentrations greater than 200 mmol/L.Transmission electron microscopy results revealed clear chloroplast outer membrane,basal lamellae distortion under 50 mmol/L stress,under 150 mmol/L stress,the inner and outer membranes of the chloroplasts showed signs of disintegration,and the mitochondrial membrane tended to be damaged,but the structure was intact,under 400 mmol/L stress,the chloroplast and mitochondria inner and outer membrane were disintegrated,and the cell structure was severely damaged.It showed that Leymus secalinus had some adaptability to Na_(2)CO_(3)stress below 150 mmol/L concentration without damaged leaf structure.