High-susceptibility of photosynthesis to photoinhibition in the tropical plant Ficus microcarpa L. f. cv. Golden Leaves

BACKGROUND: The tropical plant Ficus microcarpa L. f. cv. Golden Leaves (GL) is a high-light sensitive tropical fig tree in which sun-leaves are yellow and shade-leaves are green. We compared the response of photosynthetic activities to strong light between GL and its wild-type (WT, Ficus microcarpa L. f.). RESULTS: Field measurements of maximum photosystem II (PSII) efficiency (F(v)/F(m)) of intact sun-leaves in GL showed that photo synthetic activity was severely photoinhibited during the daytime (F(v)/F(m) = 0.46) and subsequently recovered in the evening (F(v)/F(m) = 0.76). In contrast, WT did not show any substantial changes of F(v)/F(m) values throughout the day (between 0.82 and 0.78). Light dependency of the CO(2) assimilation rate in detached shade-leaves of GL showed a response similar to that in WT, suggesting no substantial difference in photosynthetic performance between them. Several indicators of photoinhibition, including declines in PSII reaction center protein (D1) content, F(v)/F(m) value, and O(2) evolution and CO(2) assimilation rates, all indicated that GL is much more susceptible to photoinhibition than WT. Kinetics of PAM chlorophyll a fluorescence revealed that nonphotochemical quenching (NPQ) capacity of GL was lower than that of WT. CONCLUSION: We conclude that the photosynthetic apparatus of GL is more highly susceptible to photoinhibition than that of WT