Submitted to: Integrative & Comparative Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/20/2005
Publication Date: 11/30/2005
Citation: Walters, C., L.M. Hill and L.J. Wheeler. 2005. Dying while dry: kinetics and mechanisms of deterioration in desiccated organisms. Integrative and Comparative Biology 45(5):751-758. Interpretive Summary: Many organisms acquire the ability to survive complete desiccation during part of their life cycle. Once dry, the organism lives in a state of suspended animation, where few reactions appear to occur. However, reactions that cause aging continue and there is a progressive decrease in the number of dried organisms that can be resuscitated with water as storage time progresses. The longevity of different organisms stored under dry conditions ranges from a week (some bacterium) to a decade (seeds and leaves of resurrection plants). The effects of relative humidity and temperature on longevity are similar across widely varying species. This information suggests that the reactions that cause aging of dried organisms are similar, but the organisms have different levels of tolerance to these reactions. We can use this study to examine aging kinetics on realistic time scales and to determine the cellular constituents that impart tolerance and sensitivity to aging under dry conditions.
Technical Abstract: Persistence of anhydrous organisms in nature may depend on how long they remain viable in dry environments. Longevity is determined by interactions of humidity, temperature, and unknown cellular factors that affect the propensity for damaging reactions. Here we describe our research to elucidate those cellular factors and to ultimately predict how long a population can survive under extreme conditions. Loss of viability typically follows a sigmoidal pattern, where a period of small changes precedes a cataclysmic decline. The time for viability to decrease to 50% (P50) varied among seed species and among 10 phylogenetically diverse organisms. When stored at elevated temperatures of 35 degrees C and 32% relative humidity (RH), P50 ranged from about a week for spores of Serratia marcescens to several years for fronds of Selaginella lepidophylla. Most of the species studied survived longest at low humidity (10-20% RH), but suffered under complete dryness. Temperature dependencies of aging kinetics appeared similar among diverse organisms despite the disparate longevities. The effect of temperature on seed aging rates was consistent with the temperature dependency of molecular mobility of aqueous glasses, with both showing a reduction by several orders of magnitude when seeds were cooled from 60 degrees C to 0 degrees C. Longevity is an inherited trait in seeds, but its complex expression among widely divergent taxa suggests that it developed through multiple pathways.