Reaction of Photosynthetic Apparatus to Dark Desiccation Sensitively Detected by the Induction of Chlorophyll Fluorescence Quenching

Abstract

Summary Chlorophyll fluorescence parameters F0, FM, FV/FM, FV/F0, the emission and excitation spectra and induction of fluorescence quenching coefficients qp and qN were followed during the desiccation of leaf segments of spring barley (Hordeum vulgare L. cv. Akcent) and detached leaves of an endohydric moss (Rhizomnium punctatum Hedw.) exposed to the same dark-desiccation conditions (35 % air relative humidity, 24 °C). A sensitive fluorescence parameter in the initial phases of tissue desiccation was looked for. A decrease in relative water content (RWC) was much faster in the moss leaves (to 30 % RWC in 10 min) than in barley leaves (to about 30 % RWC in 17 h). A rather insensitive parameter, FV/FM, started to decrease at 60 % RWC for the moss and at 30 % RWC for the barley. A more pronounced decrease in comparison with FV/FM was observed in the case of the FV/F0. The ratio of bands (F 685/F 735) in the emission spectra at two excitation wavelengths (436 and 475 nm) was significantly changed only in desiccating R. punctatum. However, the decline in the F 685/F 735 ratio could be ascribed mostly to the increased fluorescence reabsorption. The excitation spectra were practically insensitive to the desiccation process in both species. Much more sensitive parameters reflecting the initial decrease in water content in the tissue were the qN and especially qN coefficients detected during induction elicited by the actinic light. When using the actinic irradiance for the induction similar to that of plant cultivation, the optimal interval for qP and qN detection in barley included values measured in 22 and 42 s of induction. The induction time interval of qP and qN sensitivity was much larger for the moss (included values measured in 2, 22, 42 and 62 s). Based on a distinct character of the induction curves and different changes in the F0 and FM parameters, different strategies of the barley and moss leaves in response to the same desiccation conditions were suggested.