中文摘要：

利用快速叶绿素荧光诱导动力学测定和JIP-test数据分析方法，研究了晴天条件下玉米不同朝向叶片原初光化学反应的日变化。上午朝西叶片的光合性能指数（PIABS）和PSⅡ最大量子效率（φPo）下降快，光抑制较严重；下午朝东叶片的光抑制相对较严重。一天中两组叶片的K相可变荧光占Fj-Fo振幅的比例（Wk）先上升后下降，朝东叶片捕获的激子将电子传递到电子传递链中Qi下游的其他电子受体的概率（缈。）几乎没有变化，而朝西叶片的缈。先下降后上升，表明不同朝向叶片PsⅡ受体侧和供体侧受到的伤害不同。从单位面积和单位反应中心热耗散（DIo／CS，DIo／RC）的日变化看出，上午朝西叶片过剩的激发能较多；下午朝东叶片过剩的激发能较多o与φPo相比，由JIP-test导出的其他参数如PIARS，能更好地反映光抑制的程度。且叶片的朝向不同对光抑制日变化的影响不同，在研究光合机构光抑制的日变化时，要注意叶片朝向的选择。

英文摘要：

Diurnal variations of primary photochemical reactions in maize （Zea mays L. ） leaves grown in different directions were etudied by chlorophyll a fluorescence transient measurement and the relevantly analytical method, JIP-test on sunny day. The results showed that in the forenon, the performance index on a basis of absorption （PIABs） and maximum quantum efficiency of PS Ⅱ （Cpro） decreased more drastically, suggesting the severe photoinhibition in the leaves orienting to west. However, the photoinhibition was more severely in the leaves orienting to east in the aftemon. With the variation of photon flux density （PFD）, ratio of variable fluorescence FK to the amplitude Fj - Fo（WK） increased firstly, then followed by a decrease in the two group leaves. In addition, efficiency that a trapped exciton can move an electron into the electron transport chain beyond QA （ψo） hardly varied in the leaves orienting to east, whereas that in the leaves orienting to west decreased firstly, then followed by an increase. These results demonstrate that the donor and acceptor sides of PS Ⅱ were damaged differently in the leaves orienting to different directions. Dissipation per excited cross-section or per active reaction center indicates that the excessively excited energy per cross-section or per active reaction center was higher in the leaves orienting to west at non while that was higher in the leaves orienting to east in the aftemon. Our results also exhibited that compared with φpo, other parameters derived from JIP-test such as PIABs, are more sensitive to the variation of PFD and can reflect degree of photoinhibition in maize leaves in more detail. When studying diurnal variations of photoinhibition in plant leaves, much attention should be paid on the selection for growing direction of leaves.