玉米C4光合叶不同部位解剖结构和光抑制特性的比较

以玉米第54i全展叶（C4光合叶）为材料，分别测定基部、中部和顶部的光合速率后，将叶片置于强光（2000μmol·m^2·s^-1）下处理3h和暗中恢复3h，再测定这3个部位在处理期间的叶绿素荧光参数变化；然后分别从叶片的基部、中部和顶部取样观察显微结构和超微结构，测定叶绿素含量。结果表明，3个部位光合速率和叶绿素含量的大小依次为：中部〉顶部〉基部。基部的维管束鞘细胞叶绿体数量少，体积小，排列无规律，类囊体膜有部分垛叠；中部和顶部维管束鞘细胞叶绿体数量多，体积大，大部分围绕维管束呈离心排列，类囊体膜垛叠消失。在强光下，基部、中部和顶部均发生光抑制，但光抑制程度不同，根据严重度依次为：基部〉顶部〉中部，3个部位在暗中的光抑制恢复能力依次为：中部〉顶部〉基部。与叶基部相比，叶中部在强光下能维持较高的电子传递效率（φEo）和较低的热耗散比率（φDo）。这表明，C4光合循环是保持较高电子传递效率、减轻光抑制的重要因子。

The Comparison of Anatomic Structure and Photoinhibition Characteristics between Different Regions of the C4 Photosynthetic Leaf in Maize （Zea mays L.）

After the measurement of photosynthetic rate on the basal, middle and apical regions of the 5^th fully expanded leaves （C4 photosynthesis） in maize （Zea mays L.）, the leaves were exposed to strong light （2 000μmol·m^2·s^-1） for 3 h and then transferred to dark for 3 h. During the treatments, chlorophyll fluorescence parameters were determined. Then the samples were taken from the basal, middle and apical regions of the same leaf materials to determine the chlorophyll content and observe the microstructure and ultrastructure. The results showed that, in the basal regions, the chloroplasts in bundle sheath cells are few in number, small in size and irregular in arrangement, and some thylakoid membranes are appressed; whereas, more chloroplasts with larger size presented in bundle sheath cells of the middle and apical regions, where most of chloroplasts arranged in centrifugal direction away from the vascular bundle and whose thylakoid membrane stacks disappeared. The magnitude of photosynthesis rate and chlorophyll content in the three regions of the 5^th leaves were in the order of the middle, the apical, the basal. Under strong light, photoinhibition occurred in the basal, middle and apical regions of the leaf but with varying degrees. The severities of photoinhibition in the three regions of leaves were in the order of the basal, the apical, the middle. The recovery capabilities of photoinhibition in dark fol- lowed the order of the middle, the apical, the basal. Compared with the basal, the middle regions maintained higher PSII electron transport efficiency （φEo） and less PSII heat dissipation efficiency （φDo） under strong light. Those results showed that C4 photosynthetic cycle was an important factor in maintaining higher electron transport efficiency and alleviating photoinhibition in leaves of maize.