Abstract:

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 forenoon, the performance index on a basis of absorption (PIABS) and maximum quantum efficiency of PSⅡ (φ_Po) 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 afternoon. With the variation of photon flux density (PFD), ratio of variable fluorescence F_k to the amplitude Fj-F_o (W_k) 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 PSⅡ 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 noon while that was higher in the leaves orienting to east in the afternoon. Our results also exhibited that compared with φ_Po, 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.

Key words: Maize, Diurnal change, Leaves grown in different directions, Primary photochemical reaction, Photoinhibition