Reaction of photosynthetic apparatus to dark desiccation sensitively detected by the induction of chlorophyll fluorescence quenching

Chlorophyll fluorescence parameters F-o, F-M, F-V/F-M, F-v/F-o, the emissio n and excitation spectra and induction of fluorescence quenching coefficien ts q(p) and q(N) were followed during the desiccation of leaf segments of s pring barley (Hordeum vulgare L. cv. Akcent) and detached leaves of an endo hydric moss (Rhizomnium punctatum Hedw.) exposed to the same dark-desiccati on conditions (35 % air relative humidity, 24 degrees C). A sensitive fluor escence parameter in the initial phases of tissue desiccation was looked fo r. A decrease in relative water content (RWC) was much faster in the moss l eaves (to 30 % RWC in 10 min) than in barley leaves (to about 30 % RWC in 1 7h). A rather insensitive parameter, F-v/F-M, started to decrease at 60 % R WC for the moss and at 30 % RWC for the barley. A more pronounced decrease in comparison with F-V/F-M was observed in the case of the F-v/F-o. The rat io of bands (F 685/F 735) in the emission spectra at two excitation wavelen gths (436 and 475 nm) was significantly changed only in desiccating R. punc tatum. However, the decline in the F 685/F 735 ratio could be ascribed most ly to the increased fluorescence reabsorption. The excitation spectra were practically insensitive to the desiccation process in both species. Much mo re sensitive parameters reflecting the initial decrease in water content: i n the tissue were the q(p) and especially q(N) 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 interv al for q(p) and q(N) detection in barley included values measured in 22 and 42 s of induction. The induction time interval of q(p) and q(N) sensitivit y was much larger for the moss (included values measured in 2, 22, 42 and 6 2 s). Based on a distinct character of the induction curves and different c hanges in the F-o and F-M parameters, different strategies of the barley an d moss leaves in response to the same desiccation conditions were suggested .