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

In the mosses Racomitrium lanuginosum, Anomodon viticulosus and Rhytidiadel phus loreus, after a few days air dry, F-v/F-m reached, within the first mi nute 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 m in after which further change was slow. Initial recovery of Phi (PSII) in t he light was somewhat slower, but was generally substantially complete with in a similar time. Remoistening with 0.3 mM cycloheximide (CHX) or 3 mM dit hiothreitol (DTT) made little difference to this short-term (40 min) recove ry of either F-v/F-m or Phi (PSII); 3 mM chloramphenicol (CMP) had little e ffect 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-sy nthesis inhibitors and DTT were much more clearly apparent in longer-term e xperiments (>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, CM P-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-treate d samples showed a similar but slower decline. In the shade-adapted and rel atively 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 t he 142 h of the experiment, The results indicate that in desiccation-tolera nt bryophytes recovery of photosynthesis after periods of a few days air dr y requires only limited chloroplast protein synthesis and is substantially independent of protein synthesis in the cytoplasm.