Two wavelength-dependent mechanisms of sensitisation of light-induced quenching in the isolated Light Harvesting Complex II

Stefano Santabarbara, Monika Zubik, William Remelli, Giuseppe Zucchelli and Wieslaw I. Gruszecki

The efficiency dependence of visible light in inducing fluorescence quenching in the isolated light harvesting complex II of higher plants is investigated by action spectroscopy in the visible portion of photosynthetic active radiation. The efficiency spectrum displays a relatively homogenous quenching yield across the most intense electronic transitions of the chlorophyll a and carotenoids pigments, indicating that quenching proceeds from the equilibrated state of the complex. Larger yields are observed in the 510-640 nm window, where weak transitions of LHCII bound chromophores occur. This observation is interpreted in terms of an additional quenching sensitization process mediated by these electronic transitions.