The Response of Xanthophyll Cycle-dependent Energy Dissipation in Alocasia brisbanensis to Sunflecks in a Subtropical Rainforest

Abstract

The photosynthetic responses of leaves of Alocasia brisbanensis (F.M. Bailey) Domin (Araceae) to sunflecks were monitored via chlorophyll fluorescence beneath the canopy of a subtropical rainforest in Australia. Additionally, the size and conversion state of the xanthophyll cycle were determined. Acclimation to understory environments that regularly experienced sunflecks involved small increases in the size of the xanthophyll cycle pool in comparison to understory plants that never received sunflecks. In understory plants that regularly experienced sunflecks the rate of photochemistry and the level of xanthophyll cycle-dependent energy dissipation closely tracked changes in incident PFD. Subsequent to the first sunfleck plants tended to retain their pool of xanthophyll cycle carotenoids as the deepoxidised forms (antheraxanthin and zeaxanthin) throughout the day. Retention of these deepoxidised forms apparently allows the trans-thylakoid membrane proton gradient to engage and disengage dissipation rapidly in response to a sunfleck, thereby mitigating photooxidative damage and ensuring a rapid return to efficient light utilisation via photosynthesis in limiting light. Our results were also in agreement with previous studies that demonstrated a requirement for light activation of photosynthesis.