NaCl对齿肋赤藓叶肉细胞超微结构的影响

Ultrastructural responses of Syntrichia caninervis to a gradient of Na Cl stress

齿肋赤藓(Syntrichia caninervis)是古尔班通古特沙漠苔藓结皮层中的优势物种,对荒漠生态系统的稳定性及功能多样性具有十分重要的意义。利用透射电镜技术对不同浓度Na Cl胁迫下齿肋赤藓叶肉细胞超微结构进行了观察。结果表明:齿肋赤藓叶肉细胞在未胁迫(0 mmol/L)处理下排列疏松,各种细胞结构完整,叶绿体基质排列均匀且叶绿体内含少量淀粉粒和脂质球。在轻度盐Na Cl胁迫(100 mmol/L)下,齿肋赤藓叶肉细胞结构依然保持完整,叶绿体基质均匀,叶肉细胞超微结构仅有较小变化。在中度盐Na Cl胁迫(200、300 mmol/L)下,齿肋赤藓叶肉细胞发生质壁分离,出现晶体结构,且中央大液泡发生破裂;叶绿体由梭形变成椭球形或圆球状,出现空泡化并伴随有轻微的解体;叶绿体类囊体肿胀,脂质球数量增加。在高度Na Cl胁迫(400、500 mmol/L)下,齿肋赤藓细胞的质壁分离加剧,叶肉细胞出现大量泡状结构和膜片层,叶肉细胞死亡;叶绿体片层结构消失,空泡化加重,脂质球数量增加且体积变大,叶绿体内外膜消失,叶绿体大部分解体,在叶肉细胞中几乎看不到叶绿体的存在。上述结果表明,叶绿体膜结构的损伤与盐胁迫下叶肉细胞死亡有密切关系。

Salinity is a major abiotic stress in arid and semiarid areas that has major effects on plant growth,thereby significantly reducing productivity. Biological soil crusts stabilize soil surfaces and aid in the establishment of vascular plants. These crusts have evolved salt resistance mechanisms and unique structures for survival under salinity stress and thus are an integral part of the soil system in arid regions worldwide. However,the effects of salinity on the ultrastructure of biological crusts have not been well investigated. Syntrichia caninervis Mitt is the dominant species in moss crusts of the Gurbantunggut Desert of northwestern China. In this study,S. caninervis was cultured in a concentration gradient of Na Cl solution（ 0,100,200,300,400,500 mmol / L） for 7 days. Using transmission electron microscopy,we observed changes in S. caninervis leaf cellular ultrastructure in response to salt stress. Comparisons of changes in cell wells,chloroplasts,and nuclei under the Na Cl concentrations showed that under normal conditions（ 0 mmol / L Na Cl）,mesophyll cells werearranged loosely,organelles were morphologically integrated,and starch grains and electron-dense globules（ plastoglobuli）were present in chloroplasts. No changes in ultrastructure were observed under mild Na Cl stress（ 0—100 mmol / L）; the cell structure was intact,and there were no changes in the structure of stroma or mitochondria. Under moderate Na Cl stress（ 200—300 mmol /L）,large changes in S. caninervis mesophyll cell structure were found,including swelling of the chloroplast thylakoid membranes,disorganization of grana,and plasmolysis. In addition,there was a marked increase in the number of plastoglobuli,the large central vacuole was ruptured,and chloroplasts showed disintegration. Overall,the ultrastructures of cell nuclei and vacuoles were slightly degraded. Under severe Na Cl stress（ 400—500 mmol / L）,the chloroplast membranes and lamellar structures were disorganized and contained a mass of plastoglobuli,and mesophyll cells were degraded and contained many vesicular multicycle-like membrane structures. Cells of the crust moss appeared to have serious plasmolysis as evidenced by the complete collapse of chloroplasts. These results indicate that injury to the membrane structure of various organelles,especially chloroplasts,is associated with the eventual death of mesophyll cells. Therefore,a better understanding of salinity-induced structural variability in Syntrichia caninervis should facilitate the identification of salt-tolerance mechanisms.