FEMTOSECOND TRANSIENT ABSORPTION STUDY OF CAROTENOID TO CHLOROPHYLL ENERGY-TRANSFER IN THE LIGHT-HARVESTING COMPLEX-II OF PHOTOSYSTEM-II

Singlet energy transfer between the carotenoids (Cars) and chlorophyll s (Chls) in the light-harvesting complex II (LHC II) from higher plant s has been studied using ultrafast transient absorption spectroscopy b y exciting the Cars directly in the 475-515 nm wavelength range. LHC I I trimers from Arabidopsis thaliana with well-defined Car compositions have been used. From HPLC, the wild type (WT) monomer contains two lu teins (Ls), one neoxanthin (N), and a trace of violaxanthin (V) per 12 Chls. The ABA-3 mutant contains 1.4 Ls and 0.6 zeaxanthin (Z) per mon omer. Though exploitation of the difference in Car constitution and ex citing the WT at 475 and 490 nm, and the ABA-3 mutant at 490 and 515 n m, the different Car contributions to energy transfer have been probed . Evidence for energy transfer mainly from the Car to Chl b is observe d in the WT. In the mutant, additional transfer from Car to Chl a corr elates with the presence of Z. The results imply predominant energy tr ansfer from the central Ls to Chl b which requires a modification of t he currently accepted arrangement of Chl pigments in LHC II.