Desiccation Tolerance

Resurrection plants are regarded as excellent models to study the mechanisms associated with desiccation tolerance. During the past years tremendous progress has been made in understanding the phenomenon of desiccation tolerance in resurrection plants, but many questions are open concerning the mechanisms enabling these plants to survive desiccation. The photosynthetic apparatus is very sensitive to reactive oxygen species mediated injury during desiccation and must be maintained or quickly repaired upon rehydration. The photosynthetic apparatus is a primary source of generating reactive oxygen species. The unique ability of plants to withstand the oxidative stress imposed by reactive oxygen species during desiccation depends on the production of antioxidants. The present review considers the overall strategies and the mechanisms involved in the desiccation tolerance in the first part and will focus on the effects on photosynthesis, energy metabolism and antioxidative stress defenses in the second part.► Resurrection plants use various strategies to protect cellular integrity during desiccation. ► Photosynthesis is shutdown during desiccation and completely recovered following rehydration. ► Protection against oxidative stress during desiccation is afforded by antioxidant system.

Changes in photochemical efficiency, non-radiative energy dissipation (NRD), de-epoxidation state of xanthophyll cycle components (DPS) and contents of the antioxidants ascorbic acid and glutathione were studied in leaves of the poikilohydric Ramonda serbica Panc. (Gesneriaceae) during cycles of dehydration and subsequent rehydration. In drying leaves, the intrinsic efficiency of PS II photochemistry and the photon yield of PS II electron transport showed strong progressive decreases. Simultaneously, the fraction of excitation energy dissipated as heat in the PS II antenna increased markedly. The energy-dependent component of non-photochemical quenching (NPQ) showed an increase in dehydrating leaves down to relative water contents (RWC) values near 30%. Further decreases in RWC below these values caused a decrease in NPQ. Accordingly, DPS showed a similar behaviour, with a sharp increase and a subsequent decrease at very low RWC, although the maximum DPS was reached at slightly lowe...

⎯Admittedly, the Lut Desert of Iran has been remained as an unexplored region from a microbio-logical standpoint. Domain Archaea contains extremophiles that can live in harsh habitats. Extremely halo-philic archaea are exposed to different environmental stresses in the hypersaline environments such as high solar irradiance and periodic desiccation. Haloarchaeal diversity in Shoor River, a saline river in the Lut Desert (a salinity of 134.3 g L-1 of dissolved salts), was investigated by a culture-dependent method. A large number of extremely halophilic isolates were obtained and a subset of 59 isolates was considered distinct. Firstly, the isolates were screened for their resistance under desiccation stress in 35 days. Eleven of these strains remained viable during the period in a desiccator containing silica gel. Then, three of them were randomly selected and their resistance against desiccation and ionizing radiation were determined. The isolates MS2, MS17, and MS50 were still recovered after 8 weeks in a desiccator and were moderately resistant to gamma radiation with D 10 value between 2 and 3 kGy. Strains MS2, MS17, and MS50 were affiliated with three species in the family Halobacteriaceae using 16S rRNA gene sequence analysis as well as morphological and biochemical characteristics-Haloterrigena jeotgali A29 T (99.6% similarity), Natrialba aegyptia 40 T (99.4% similarity) and Natrinema pallidum NCIMB 777 T (99.3% similarity), respectively. Although resistance to desiccation did not follow the sigmoid survival curve pattern of Deinococcus radiodurans, apparently haloarchaea can show a more resistance to desiccation in more long-term periods of time. This is the first report on isolation of extremely halophilic archaea belonged to the family Halobacteriaceae and their radioresistance and desiccation tolerance properties isolated from the Shoor River.