PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

ODMR of carotenoid triplet states associated with the long emitting chlorophylls of PSI. Donatella Carbonera^*,1, Stefano Santabarbara², ¹ Chemical Sciences Department, Padova, Italy² School of Biological Science, London, United Kingdom

ABSTRACT- Two main classes of carotenoids are found in the photosystems of higher plants: the xanthophylls, including lutein, violaxantin, neoxantin and zeaxantin, which are found in both LHC I and LHC II outer antenna complexes; beta-carotene, which is present in the inner antenna and reaction centre binding complex of both PS II and PS I. Carotenoids, in photosynthetic systems, are known to have multiple functions. They play a significant role in the stabilisation of folding of Chl binding polypeptides, are effective in collecting and transferring energy and play a physiological protective role by avoiding the formation of singlet oxygen, which could be generated from the interaction of the excited triplet state of chlorophyll and the oxygen ground state. The xanthophylls are also involved in the non-photochemical quenching. The efficiency of Chl triplet quenching by protein-bound carotenoids has been estimated in between 0.8 and the unity depending on the system and on the temperature. The Carotenoids triplet states associated with the light harvesting complexes of PS I and PS II have been investigated in isolated spinach thylakoids by means of Fluorescence Detected Magnetic Resonance (ODMR). While carotenoid triplet states associated with the inner and, especially, the main outer antenna complex of PS II, LHCII, have been investigated before in details by means of transient optical and magnetic resonance spectroscopic techniques, the carotenoids triplets associated with PS I of higher plants are poorly characterised. In the present study we present an analysis of the carotenoids triplet states associated with the red emitting forms of thylakoids isolated from spinach studied by means of Fluorescence Detected Magnetic Resonance (FDMR) technique. At least four carotenoid triplet populations have been characterised, which are assigned, based on the associated microwave-induced emission profiles, to long absorbing polypeptides of LHC-I.

KEY WORDS: triplet, carotenoid, ODMR, LHC I