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

摘要

Leaf segments of spring barley cv. Akcent and detached leaves of the endohydric moss Rhizomnium punctatum were desiccated in the dark at 35% RH and 24deg C. The decrease in relative water content (RWC) was much faster in the moss leaves (to 30% RWC in10 min) than in barley leaves (to about 30% RWC in 17 h). A fairly insensitive chlorophyll fluorescence parameter, FV/FM, started to decrease at 60% RWC in the moss and 30% RWC in barley. A more pronounced decrease was observed in the case of FV/F0. Theratio of bands (F 685/F 735) in the emission spectra at 2 excitation wavelengths (436 and 475 nm) was significantly altered 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 not sensitive to the desiccation process in either species. Much more sensitive parameters, reflecting the initial decrease in water content in the tissue, were the qP and especially qN coefficients detectedduring induction elicited by actinic light. When using actinic irradiance for induction, the optimal interval for qP and qN detection in barley was 22-42 s after the start of induction. The induction time interval of qP and qN sensitivity was much larger for the moss (2-62 s). Based on the distinct characters of the induction curves and different changes in the F0 and FM parameters, different strategies for barley and moss leaves in response to the same desiccation conditions were suggested.