Dying while Dry: Kinetics and Mechanisms of Deterioration in Desiccated Organisms

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°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°C to 0°C. Longevity is an inherited trait in seeds, but its complex expression among widely divergent taxa suggests that it developed through multiple pathways.

Water potential and viability of seeds of Eugenia (Myrtaceae), a tropical tree species, based upon different levels of drying

“…4 showed that the viability was not lost at -20MPa for most of the species, i.e. when cells were in the dry state (Walters et al 2005). Studies on seed desiccation tolerance based upon Ψ have been developed (Pritchard 1991;Farrant and Walters 1998;Eira et al 1999;Sun and Liang 2001;Daws et al 2006), but much less than those based upon the WC.…”

“…Delgado and Barbedo (2007), for example, identified three different levels of critical water content (described as fresh mass basis) for the seeds of six species of Eugenia, from 65 (the most sensitive seeds) to 45% (the least sensitive seeds). However, there is little information on the desiccation tolerance for the seeds of Eugenia in terms of water potential, making it difficult to understand the metabolic events occurring at different levels of water activity, as described by Vertucci and Farrant (1995) and Walters et al (2005). In the present work, we describe the relationship between the water potential and viability for the seeds of six Brazilian species of Eugenia (E. brasiliensis Lam., E. cerasiflora Miq., E. involucrata DC., E. pyriformis Camb., E. umbelliflora Berg.…”

“…More recently, researchers have described this desiccation tolerance in terms of water potential (Sun and Liang 2001;Sun 2002;Villela et al 2003;Daws et al 2006), or water activity (Sun 2002;Faria et al 2004), which could better describe the status of the water and, probably, the real desiccation tolerance of the seeds. According to Walters et al (2005), fully hydrated seeds (Ψ ≥ ~ -1MPa) could grow. Stress responses which could be detected at hydration levels lower than -1MPa were initially the expression of stressrelated proteins and nucleic acid repair pathways (-1 to ~ -3MPa) followed by the rampant production of free radicals and loss of membrane integrity .…”

The expression pattern of dormancy-associated genes in multiple life-history stages in the rotifer Brachionus plicatilis

“…hatching of resting eggs) involves a large, sometimes sudden, increase in oxygen uptake and ROS generation. Maintaining high constitutive anti-oxidative defences is one way of coping with these phenomena (Walters et al, 2005;Storey & Storey, 2007;Bailly et al, 2008). Consequently, five paralogs of the ferritin family show higher expression patterns in resting eggs; ferr-2, ferr-3, ferr-4, ferr-6 and ferr-7 (Fig.…”

Editorial: special issue GROW “plant desiccation stress”

“…Typically for ex situ conservation purposes seeds are stored in seed banks in which they are maintained in the desiccated state at temperatures of -18°C (conventional storage) or in the vapour of liquid nitrogen at -120 to -150°C (cryogenic storage). Orthodox seeds have been maintained viable under such conditions for more than 30 years, with predictions of considerably longer life spans (Walters et al 2005). DS seeds are killed if dried and suffer lethal ice crystal damage if stored hydrated under such low temperature conditions.…”