The Car S-1 -> Chl energy transfer efficiency, Phi(Transfer) in xanthophyll-cycle mutants of living plants and LHC II was investigated by selective Car S, two-photon excitation. Before high-light illumination Phi(Transfer), of the violaxanthin deficient mutant npq2 is similar to 30% smaller than the corresponding value for wild type plants. For the zeaxanthin deficient mutant, npq1, Phi(Transfer) is similar to 30% larger. Wild type Arabidopsis thaliana is the only variant which is capable of a light-dependent decrease of up to 40% and complete recovery to the original Phi(Transfer) values, In contrast, Phi Transfer remains constant during dark adaptation in both mutants. Surprisingly, changes in Phi Transfer of LHC II preparations were less than 5% only, when substituting violaxanthin by zeaxanthin. (c) 2007 Elsevier B.V. All rights reserved.