To evaluate the effect of inclination angle of the leaf on the leaf injury of rice by O
3, we examined the effect of a 5-hr exposure to 0, 0.1, 0.3 cm
3 m
-3 O
3, abbreviated as O
0, O
0.1 and O
0.3, respectively, of the flag leaf using natural-light gas-exposure chambers. The middle portion of the flag leaf was set horizontally using lead weights (H plant) and it was compared with a non-treated, erect leaf (E plant). Gas exchange and chlorophyll fluorescence were measured immediately before, immediately after, and 1 and 3 d after the start of the exposure. The net photosynthetic rate, stomatal conductance and operating quantum efficiency of photosystem II (F
q’/F
m’) were decreased by the exposure to O
3. Furthermore, the inhibitory effects of O
0.1 and O
0.3 on the H plants were severer than those on the E plants. The maximum quantum efficiency of photosystem II (F
v/F
m) in the leaf of H plants decreased immediately after exposure to O
3. These results indicate that the weaker inhibitory effect of O
3 on the erect leaf depends on the lower light intensity at the leaf surface, rather than the horizontal leaf position.
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