低温胁迫对烤烟幼苗光合荧光特性及叶片结构的影响

为探明苗期烟草响应低温胁迫的光合生理机制，对烤烟品种红花大金元和K326进行了低温胁迫0 h（CK）、3 h、6 h、12 h、24 h和48 h处理，研究了低温胁迫对光合作用参数、叶绿素荧光参数、叶片组织结构和叶绿体超微结构的影响。结果表明:低温胁迫下，叶片净光合速率（Pn）、气孔导度（Gs）、胞间CO₂浓度（Ci）和蒸腾速率（Tr）显著降低，水分利用效率（WUE）和气孔限制值（Ls）显著升高；非光化学猝灭系数（NPQ）显著升高，PS Ⅱ最大光化学效率（Fv/Fm）、PS Ⅱ潜在活性（Fv/Fo）、PS Ⅱ有效光化学量子效率（Fv'/Fm'）、PS Ⅱ实际光化学量子效率（Φ_{PS Ⅱ}）、光合电子传递效率（ETR）和光化学猝灭系数（q_P）显著降低；冷敏感品种K326叶片厚度、栅栏组织厚度、海绵组织厚度和栅栏组织/海绵组织比显著降低，叶片细胞发生质壁分离，叶绿体发生形变，基粒片层排列松散，淀粉粒增大，嗜锇颗粒增多。低温胁迫下，红花大金元较K326具有较强的耐受性，苗期烟草叶片厚度减小和叶绿体超微结构受损是导致光能转化效率和净光合速率降低的主要原因。 

Effects of low temperature stress on photosynthetic fluorescence characteristics and leaf tissue structure of flue-cured tobacco seedlings

With the aim to investigate photosynthetic physiological mechanism of tobacco in response to low temperature stress, two cultivars of flue-cured tobacco seedlings (Honghuadajinyuan and K326) were treated with 4℃ for 0h (CK), 3h, 6h, 12h, 24h and 48h to study the effect on photosynthetic parameters, chlorophyll fluorescence parameters, leaf tissue structure and chloroplast ultrastructure under low temperature stress. Results showed that net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration and transpiration decreased significantly, while water use efficiency and stomatal limitation increased significantly with prolonged stress time. The determination of chlorophyll fluorescence parameters revealed that non-photochemical quenching coefficient increased significantly, but PS Ⅱ maximal photochemical efficiency, PS Ⅱ potential activity, PS Ⅱ effective quantum efficiency, PS Ⅱ actual photochemical quantum efficiency, photosynthetic electron transport rate and photochemical quenching coefficient decreased significantly. Anatomical structure of K326 revealed that leaf thickness, palisade tissue thickness, spongy tissue thickness and palisade tissue/spongy thickness decreased significantly. Ultrastructure showed that the phenomenon of plasmolysis generally appeared, chloroplasts were deformed, granules were arranged loosely, starch granules increased, and osmiophilic globule increased. Under low temperature stress, Honghuadajinyuan was more tolerant than K326, and the decrease of leave thickness and damage of chloroplast ultrastructure in tobacco seedlings were the main factors leading to the decrease of light energy conversion efficiency and net photosynthetic rate.