Correlations between chlorophyll fluorescence quenching parameters and photosynthesis in a segregating Lycopersicon esculentum x L-peruvianum population as measured under constant conditions

Chl fluorescence of mature leaves in low-temperature treated plants was stu died under identical measuring conditions in a segregating population of th e F-3 offspring of a cross between a chilling-tolerant and a chilling-sensi tive tomato species. Through recombination of genes involved in photosynthe sis, the population revealed a wide, continuous variability of photosynthet ic capacity from plants performing much worse to those performing better th an the parental lines of the cross. In the parental species, a nearly linea r correlation was observed between photochemical chl fluorescence quenching (q(P)) and O-2 evolution over a wide temperature range. Across the F3 gene ration, still a weak correlation between the two parameters was found at 20 degrees C, but not at 10 degrees C, when measured under identical conditio ns. This indicates that the fraction of open reaction centres could at leas t in part be adjusted to the photosynthetic capacity of the individual geno type. However, the correlation was so weak, that the previously suggested u se of q(P) as a selection criterion for chilling tolerance of photosynthesi s in breeding programs is regarded as doubtful, as long as photosynthesis r ates are not measured in addition. Quantum efficiency of Photosystem II (Ph i(P)S II) was strongly dependent on q(P) both at 20 and at 10 degrees C mea suring temperature and depended on the quantum efficiency of open reaction centres (F-v'/F-m') at 20, but not at 10 degrees C. F-v'/F-m', in turn, cor related negatively with the processes of energy dissipation by the mechanis ms of non-photochemical quenching (q(N)), i.e. its fast-relaxing component (q(F)) and photoinhibitory quenching (q(I)).