Rapid recovery of photosystems on rewetting desiccation-tolerant mosses: chlorophyll fluorescence and inhibitor experiments

In the mosses Racomitrium lanuginosum, Anomodon viticulosus and Rhytidiadelphus loreus, after a few days air dry, F-v/F-m reached, within the first minute of remoistening in the dark, two-thirds or more of the value attained after 40 min. A fast initial phase of recovery was completed within 10-20 min after which further change was slow. Initial recovery of Phi (PSII) in the light was somewhat slower, but was generally substantially complete within a similar time. Remoistening with 0.3 mM cycloheximide (CHX) or 3 mM dithiothreitol (DTT) made little difference to this short-term (40 min) recovery of either F-v/F-m or Phi (PSII); 3 mM chloramphenicol (CMP) had little effect on recovery of F-v/F-m, but resulted in substantial (though not total) depression of Phi (PSII) and (CO2)-C-14 uptake. Effects of the protein-synthesis inhibitors and DTT were much more clearly apparent in longer-term experiments (>20 h) but only in the light. In the dark, the three inhibitors had at most only slight effects over periods of 60-100 h. In the light, CMP-treated samples of all three species showed a progressive decline of dark-adapted F-v/F-m, falling to zero within 1-5 d (possibly due to blocking of the turnover of the D1 protein of PSII) and accelerated by DTT. CHX-treated samples showed a similar but slower decline. In the shade-adapted and relatively desiccation-sensitive Rhytidiadelphus loreus, slow recovery of F-v/F-m continued in the dark even in the presence of CMP and CHX for much of the 142 h of the experiment, The results indicate that in desiccation-tolerant bryophytes recovery of photosynthesis after periods of a few days air dry requires only limited chloroplast protein synthesis and is substantially independent of protein synthesis in the cytoplasm.