Desiccation-induced ultrastructural and biochemical changes in the leaves of the resurrection plant Myrothamnus flabellifolia

Abstract

Light microscopy and low-temperature scanning electron microscopy were used to systematically compare the surface and internal ultrastructures of hydrated and desiccated leaves of the resurrection plant Myrothamnus flabellifolia (Welw.). This revealed that leaf tissue underwent considerable shrinkage and collapse on desiccation but was supported by a framework of vascular and sclerenchymous tissue, which is responsible for the fan-like shape of the leaves. In addition, the leaf ribs were covered with wax and an internal wax cuticle was observed. Biochemical analysis showed that the cyanidin 3-glucoside content increased on desiccation as did the trehalose and sucrose contents. Salt deposits were observed at the apices of desiccated leaves in the proximity of hydathode-like structures. We propose that this might regulate the leaf salt content since decreased intracellular cation concentration was observed in desiccated leaves. We believe that these unique adaptations contribute to the remarkable desiccation-tolerance properties of this plant.

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

“…In M. flabellifolius [55], wall folding occurs in the epidermis (around seemingly less flexible stomata and gland cells) and in the adjacent mesophyll cells [30]. In this species, there were no significant changes in wall components during drying, but walls contained an unusually high amount of arabinose.…”

“…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].…”

“…Moore et al [49] have shown that dry leaves of M. flabellifolia contain a high proportion (up to 50% of the leaf dry weight) of 3, 4, 5 tri-O-galloylquinic acid that acts as a potent antioxidant [49]. Although this polyphenol is predominantly located in the vacuole, it has been proposed to act as an antioxidant reservoir linked to the cytoplasmic antioxidants and function as a redox buffer [30,49,50].…”

“…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.…”

“…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. The content of vacuoles from desiccated leaves of E. nindensis was analyzed after nonaqueous extraction and was shown to contain proline, sucrose, and protein in equal proportions [58].…”