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.
Acta Agronomica Sinica
Leaves grown in different directions
Primary photochemical reaction, Photoinhibition