Most higher plants are unable to survive desiccation to an air-dried state. An exception is a small group of vascular angiosperm plants, termed resurrection plants. They have evolved unique mechanisms of desiccation tolerance and thus can tolerate severe water loss, and mostly adjust their water content with the relative humidity in the environment. Desiccation tolerance is a complex phenomenon and depends on the regulated expression of numerous genes during dehydration and subsequent rehydration. Most of the resurrection plants have a large genome and are difficult to transform which makes them unsuitable for genetic approaches. However, technical advances have made it possible to analyze changes in gene expression on a large-scale. These approaches together with comparative studies with non-desiccation tolerant plants provide novel insights into the molecular processes required for desiccation tolerance and will shed light on identification of orphan genes with unknown functions. Here, we review large-scale recent transcriptomic, proteomic, and metabolomic studies that have been performed in desiccation tolerant plants and discuss how these studies contribute to understanding the molecular basis of desiccation tolerance.

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Desiccation tolerance in resurrection plants: new insights from transcriptome, proteome and metabolome analysis

Antioxidant system in sporobolus stapfianus: changes in response to desiccation and rehydration

Resurrection plants are a small but diverse group of land plants characterized by their tolerance to extreme drought or desiccation. They have the unique ability to survive months to years without water, lose most of the free water in their vegetative tissues, fall into anabiosis, and, upon rewatering, quickly regain normal activity. Thus, they are fundamentally different from other drought-surviving plants such as succulents or ephemerals, which cope with drought by maintaining higher steady state water potential or via a short life cycle, respectively. This review describes the unique physiological and molecular adaptations of resurrection plants enabling them to withstand long periods of desiccation. The recent transcriptome analysis of Craterostigma plantagineum and Haberlea rhodopensis under drought, desiccation, and subsequent rehydration revealed common genetic pathways with other desiccation-tolerant species as well as unique genes that might contribute to the outstanding desiccation tolerance of the two resurrection species. While some of the molecular responses appear to be common for both drought stress and desiccation, resurrection plants also possess genes that are highly induced or repressed during desiccation with no apparent sequence homologies to genes of other species. Thus, resurrection plants are potential sources for gene discovery. Further proteome and metabolome analyses of the resurrection plants contributed to a better understanding of molecular mechanisms that are involved in surviving severe water loss. Understanding the cellular mechanisms of desiccation tolerance in this unique group of plants may enable future molecular improvement of drought tolerance in crop plants.

https://link.springer.com/content/pdf/10.1007/s00018-012-1088-0

Molecular mechanisms of desiccation tolerance in resurrection plants

While many vascular plants produce specialized structures that are able to withstand desiccation (e.g., seeds, spores, or pollen), few can survive severe water loss in the vegetative state. The vast majority of desiccation-tolerant plants belong to the lower groups of the plant kingdom: algae, lichens, and bryophytes. They are poikilohydric in nature and exhibit a rapid equilibration of their internal water content with the water potential of the environment. A few ferns, and even fewer angiosperms are tolerant of desiccation (Davis 1972; Gaff 1980; Bewley and Krochko 1982); they exhibit modified poikilohydry, however, since most have features (e.g., stomatal complexes) that permit them to reduce their rate of water loss.

Desiccation Tolerance in Vegetative Plant Tissues and Seeds: Protein Synthesis in Relation to Desiccation and a Potential Role for Protection and Repair Mechanisms

This chapter discusses structural and physiological features of poikilohydrous autotrophs and the different strategies in different ecological situations. It presents examples of poikilohydrous autotrophs living under very limiting ecological conditions in many different regions of the Earth. Nonvascular autotrophs are considered constitutively poikilohydrous because they lack the means of controlling water relations. In Africa, subfruticose poikilohydrous plants such as Lindernia crassifolia and Lindernia acicularis grow in sheltered rock niches. Poikilohydrous autotrophs, therefore, have had to trade-off between surviving desiccation against uptake, transport, and storage of water. Poikilohydrous plants that possess an internal system for water transport are exposed to cavitation during desiccation, which compromise the functioning of the conducting tissues upon rehydration. Poikilohydrous autotrophs can maintain their water content at a constant level only to a limited extent, but they can extend hydration into the dry period by certain, mostly structural, mechanisms.

2 Opportunistic Growth and Desiccation Tolerance: The Ecological Success of Poikilohydrous Autotrophs

Nitrogen contents were determined in 20 species of “resurrection plants”,i.e. plants with leaves which are able to revive from an air-dry state (viz. Boea hygroscopica, Borya nitida, Cheilanthes sieberi, Coleochloa pallidior, C. setifera, Craterostigma plantagineum, Myrothamnus flabellifolia, Oropetium capense, Pellaea calomelanos, P. falcata, P, viridis, Polypodium polypodioides, Ramondia pyrenaica, Selaginella lepidophylla, Sporobolus stapfianus, Talbotia elegans,Tripogon loliiformis, Xerophyta retinervis, X. villosa, X. viscosa), and in three desiccation sensitive species (Eragrostis tenuifolia, Selaginella kraussiana andSporobolus pyramidalis). In a preponderance of resurrection plants insoluble nitrogen content fell during dehydration of intact plants and soluble non-protein N rose. Both changes were particularly marked in species which lose chlorophyll and thylakoid structure during drying. These trends were usually only partially reversed after 24 h rehydration. Recovery of14C-leucine incorporation in rehydrating leaves was slow. Leaves of desiccation sensitive vascular plants tended on the average to lose soluble protein rather than insoluble N during drying, and tended to have higher soluble non-protein N contents than tolerant plants. However, similarity in the changes in N-contents inXerophyta villosa leaves killed by airdrying compared to leaves surviving air-drying, opposes the view that death was due to excessive loss of protein.

D. F. Gaff

Papers

The effect of dehydration and rehydration on the nitrogen content of various fractions from resurrection plants