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Many desiccation induced late embryogenesis abundant (LEA) protein encoding genes have been identified from Craterostigma plantagineum Hochst. In the desiccation tolerant plants C. plantagineum (Cp) and Lindernia brevidens Skan (Lb) transcripts encoding LEA-like 11-24 protein are abundantly expressed during desiccation whereas in Lindernia subracemosa De Wild. (Ls), a desiccation sensitive plant, the LEA-like 11-24 transcripts are expressed at a low level. Since promoters determine gene expression, a comparative promoter analysis was carried out to decipher the underlying mechanisms of differential gene expression. Two transient transformation methods (particle bombardment and optimised Agrobacterium co-cultivation) were used to analyse the promoter activities of the Cp, Lb and Ls LEA-like 11-24 gene in homologous and heterologous systems. Minimal promoters were isolated from all three species and their promoter activities were assessed in response to mannitol or ABA. Particle bombardment or Agrobacterium co-cultivation yielded similar results. Site-directed mutagenesis was used to identify which cis-acting elements in the LEA-like 11-24 promoter fragments are crucial during mannitol and ABA treatments. The presence of these promoter cis-elements explains the differences in transcript abundance in the desiccation tolerant and desiccation sensitive species. Results indicated the importance of the drought responsive elements (DRE) element for promoter activity.

The relationship between the accumulation of D-glycero-D-ido-octulose (D-g-D-i-oct) and sucrose and desiccation tolerance was analysed in leaves of Craterostigma plantagineum Hochst. in various conditions. The D-g-D-i-oct level is strictly controlled in C. plantagienum. Light is an important factor enhancing D-g-D-i-oct synthesis when exogenous sucrose is supplied. Desiccation tolerance is lost during natural senescence and during sugar starvation that leads to senescence. The differences in expression patterns of senescence-related genes and the carbohydrate status between vigorous and senescent plants indicate that desiccation tolerance and accumulation of octulose in C. plantagineum is dependent on the developmental stage. Sucrose synthesis is affected more by dehydration than by senescence. D-g-D-i-oct has superior hydroxyl scavenging ability to other common sugars accumulating in C. plantagineum. In the presence of reactive oxygen species (ROS) D-g-D-i-oct levels decreased, probably as a defence reaction.

Salinity is one of the major abiotic stress factors that drastically reduces agricultural productivity. In natural environments salinity often occurs together with other stresses such as dehydration, light stress or high temperature. Plants cope with ionic stress, dehydration and osmotic stress caused by high salinity through a variety of mechanisms at different levels involving physiological, biochemical and molecular processes. Halophytic plants exist successfully in stressful saline environments, but most of the terrestrial plants including all crop plants are glycophytes with varying levels of salt tolerance. An array of physiological, structural and biochemical adaptations in halophytes make them suitable models to study the molecular mechanisms associated with salinity tolerance. Comparative analysis of plants that differ in their abilities to tolerate salinity will aid in better understanding the phenomenon of salinity tolerance. The halophyte Thellungiella salsuginea has been used as a model for studying plant salt tolerance. In this review, T. salsuginea and the glycophyte Arabidopsis thaliana are compared with regards to their biochemical, physiological and molecular responses to salinity. In addition recent developments are presented for improvement of salinity tolerance in glycophytic plants using genes from halophytes.

For the first time in the grasses, a desiccation-tolerant species (Sporobolus stapfianus) was examined for evidence of drought-induced changes in gene transcription. Desiccation tolerance (the ability of this species to recover from a water potential of –540 MPa) is induced in the resurrection grass during the drying process itself. Specific mRNA was compared in extracts of air-dry, drying and fully hydrated leaves by comparisons of the encoded proteins translated in vitro and partitioned by 2- dimensional electrophoresis. Forty-one genes, that were not expressed in hydrated leaves, were transcribed during drying, whereas only 25 novel polypeptides (translated in vitro) were detected; this suggests that gene expression was controlled mainly at the transcriptional level, but possibly also at the translational level. Leaves of S. stapfianus become desiccation tolerant as they dry on intact plants with mechanically undisturbed roots, whereas leaves on plants whose roots have been disturbed die during drying. Complements of mRNA from live S. stapfianus leaves changed markedly from full hydration to 70% RWC and to air-dryness; they also differed markedly from drought-sensitive leaves (on plants with disturbed roots) at 70% RWC and dead air-dry S. stapfianus leaves and from leaves of the desiccation sensitive grass S. pyramidalis at the same water contents. Drought-induced injury could not be attributed to low abundance of mRNA in either species. Five criteria which might be involved in desiccation tolerance were applied to specific in vitro proteins of S. stapfianus; 12 novel proteins correlated with desiccation tolerance in a least four of the five criteria.