The rate of drying determines the extent of desiccation tolerance in Physcomitrella patens

The effect of differential drying rates on desiccation tolerance in Physcomitrella patens (Hedw.) Bruch & Schimp. is examined. In order to provide more evidence as to the status of desiccation tolerance in P. patens, a system was designed that allowed alteration of the rate of water loss within a specific relative humidity. An artificial substrate consisting of layers of wetted filter paper was used to slow the drying process to as long as 284 h, a significant increase over the commonly used method of exposure (saturated salt solution). By slowing the rate of drying, survival rates and chlorophyll fluorescence parameters improved, and tissue regeneration time was faster. These results indicate a trend where the capacity for desiccation tolerance increases with slower drying, and reveal a much stronger capacity for desiccation tolerance in P. patens than was previously known.