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

<p>Abstract</p> <p>Background</p> <p>The tropical plant <it>Ficus microcarpa</it> 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, <it>Ficus microcarpa</it> L. f.).</p> <p>Results</p> <p>Field measurements of maximum photosystem II (PSII) efficiency (<it>F</it>_v/<it>F</it>_m) of intact sun-leaves in GL showed that photo synthetic activity was severely photoinhibited during the daytime (<it>F</it>_v/<it>F</it>_m = 0.46) and subsequently recovered in the evening (<it>F</it>_v/<it>F</it>_m = 0.76). In contrast, WT did not show any substantial changes of <it>F</it>_v/<it>F</it>_m values throughout the day (between 0.82 and 0.78). Light dependency of the CO₂ 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, <it>F</it>_v/<it>F</it>_m value, and O₂ evolution and CO₂ assimilation rates, all indicated that GL is much more susceptible to photoinhibition than WT. Kinetics of PAM chlorophyll <it>a</it> fluorescence revealed that nonphotochemical quenching (NPQ) capacity of GL was lower than that of WT.</p> <p>Conclusion</p> <p>We conclude that the photosynthetic apparatus of GL is more highly susceptible to photoinhibition than that of WT.</p>