Effects of desiccation on the 77°K fluorescence properties of the liverwort Porella navicularis and the isolated lichen green alga Trebouxia pyriformis

Abstract

The liverwort Porella navicularis and the isolated lichen green alga Trebouxia pyriformis were desiccated in darkness and light. Low temperature (77°K) fluorescence emission spectra were deconvoluted into band components by RESOL. The reasons for the desiccation‐induced decreases of fluorescence yield, particularly of the PSII emission bands, were analyzed by following fluorescence kinetics of PSI and PSII during PSII trap closure at 77°K, and by the determination of two point relative action spectra for PSI and PSII emissions upon excitation of chlorophyll a or b preferentially.It was concluded that the pronounced loss of FII in Porella was largely accomplished by a strong decrease in the rate constant for fluorescence (kFII), whereas the energy transfer from PSII to PSI, (kT(II→I)), was unaffected or slightly decreased. Desiccation of Porella also decreased α, the fraction of absorbed light distributed initially to PSI. Unlike Porella, Trebouxia responded to desiccation by only a small decrease in fluorescence. The drop in FII was probably due to a 10–20% increase in kT(II→I); kFII was unaffected. No significant changes in α were observed in Trebouxia. A general lowering of the fluorescence yields of both species was probably also mediated by some PSII reaction center quenching of Fv in the dry samples. The results of two point relative action spectra confirmed the above findings and it was assumed that the more pronounced effects of light drying compared to that of dark drying, were mediated by changes in similar parameters. The difference in desiccation responses between Porella and Porphyra (Öquist and Fork 1982) are discussed and assumed to be related to the different habitats of these two species, deep shade vs exposed sun, respectively.