Abstract
The majority of flowering-plant species can survive complete air-dryness in their seed and/or pollen. Relatively few species (‘resurrection plants’) express this desiccation tolerance in their foliage. Knowledge of the regulation of desiccation tolerance in resurrection plant foliage is reviewed. Elucidation of the regulatory mechanism in resurrection grasses may lead to identification of genes that can improve stress tolerance and yield of major crop species. Well-hydrated leaves of resurrection plants are desiccation-sensitive and the leaves become desiccation tolerant as they are drying. Such drought-induction of desiccation tolerance involves changes in gene-expression causing extensive changes in the complement of proteins and the transition to a highly-stable quiescent state lasting months to years. These changes in gene-expression are regulated by several interacting phytohormones, of which drought-induced abscisic acid (ABA) is particularly important in some species. Treatment with only ABA induces desiccation tolerance in vegetative tissue of Borya constricta Churchill. and Craterostigma plantagineum Hochstetter. but not in the resurrection grass Sporobolus stapfianus Gandoger. Suppression of drought-induced senescence is also important for survival of drying. Further research is needed on the triggering of the induction of desiccation tolerance, on the transition between phases of protein synthesis and on the role of the phytohormone, strigolactone and other potential xylem-messengers during drying and rehydration.
Highlights
The ability of leaves to survive dehydration below 5% relative water content is found in a very small proportion of angiosperm species
Have yet to be examined as possible root-to-shoot signals in the induction of desiccation tolerance: CLAVATA3/EMBRYO-surrounding region-related 25 (CLE25) synthesized in droughted Arabidopsis roots is transmitted in the vascular system to leaves where it acts with BARELY ANY MERISTEM (BAM) receptors to influence abscisic acid (ABA)-synthesis and thereby produces closure of stomata [97]
While trehalose is the major protective sugar that accumulates in some desiccation-tolerant species, such as nematodes and tardigrades, sucrose is the predominant protective sugar accumulating in drying resurrection plants, with trehalose and other sugars accumulating at lower levels [64]
Summary
The ability of leaves to survive dehydration below 5% relative water content is found in a very small proportion of angiosperm species. In most such ‘resurrection’ species, desiccation tolerance is induced in them in the early stage of drying by the drought stress itself [1]. The occurrence of desiccation tolerance in the foliage of 39 species of grasses (Table 1) is of particular interest in view of the importance of the family Poaceae for agriculture and grazing. Watch?v=tGg-_tOiUvA for a summary, including time-lapse video, of resurrection plants reviving).
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