Desiccation tolerance in the vegetative tissues of the fern Mohria caffrorum is seasonally regulated

Abstract

SummaryAs there is limited information on the mechanisms of vegetative desiccation tolerance in pteridophytes, we undertook a comprehensive anatomical, ultrastructural, physiological and biochemical study on the fern Mohria caffrorum. Our data show that this species is desiccation-tolerant during the dry season, and desiccation-sensitive in the rainy season. This system allows the verification of protection mechanisms by comparison of tolerant and sensitive tissues of the same species at the same developmental age. Tolerant fronds acquire protection mechanisms during drying that are mostly similar to those reported for angiosperms. These include: (i) chlorophyll masking by abaxial scales and frond curling; (ii) increased antioxidant capacity that is maintained in dry tissues; (iii) mechanical stabilization of vacuoles in the dry state; (iv) de novo production of heat stable proteins (at least one identified as a putative chaperonin); (v) accummulation of protective carbohydrates (sucrose, raffinose family oligosaccharides and cyclitols). This study has implications for the biotechnological production of drought-tolerant crops, and allows speculation on the evolution of vegetative desiccation tolerance.

A Systems‐Based Molecular Biology Analysis of Resurrection Plants for Crop and Forage Improvement in Arid Environments

“…and E. nindesis). This supports the contention that homoiochlorophyllous resurrection plants might need better antioxidant protection against free radical activity than the poikilochlorophyllous ones [14,23].…”

“…In contrast, homoiochlorophyllous species, commonly dicotyledons, retain most of their chlorophyll and thylakoid membranes intact during desiccation. They utilize various adaptations to prevent ROS production from photoactivated chlorophyll uncoupled from metabolic dissipation mechanisms (thylakoid membranes channeling excited electron to oxygen production) [22,23,29]. This is achieved by leaf folding and shading of inner leaves (e.g., the Craterostigma spp.)…”

“…This is achieved by leaf folding and shading of inner leaves (e.g., the Craterostigma spp.) or adaxial surfaces (e.g., M. flabellifolius and M. caffrorum), utilizing reflective hairs and/or waxes and usually sunscreen pigments (anthocyanins and phenols), to reflect light back away from the leaf surface [22,29,30].…”

“…[51,52] and (ii) increased vacuolation with water replacement in vacuoles by nonaqueous substances such as in the Xerophyta spp. ( [23], see Figure 17.2 for ultrastructural changes to resurrection plants). Desiccation induced cell wall folding is essential for structural preservation of tissue [53] and the extent and manner of folding is species specific and depends upon the chemical composition and molecular architecture of the cell wall.…”

“…Replacement of water in vacuoles within dry tissues of resurrection plants was first suggested on the basis of ultrastructural observations that vacuoles continue to take up a large proportion of the cytoplasmic space despite the fact that there was no longer bulk water available in tissues, the remaining water being purely structure associated [14,23,30,58]. A thorough biochemical analysis of M. flabellifolius [30,49] revealed that the vacuoles (both hydrated and dry) contained the 3,4,5 tri-o-galloylquinic acid and that this polyphenolic increased upon drying to fill the vacuole and stabilize the subcellular milieu against mechanical stress.…”