Exploring the polysaccharide composition of plant cell walls in succulent aloes

Abstract

Societal Impact Statement Aloes are iconic succulent plants native to Africa, Madagascar and the Arabian Peninsula. The succulent leaf mesophyll of aloes has been used extensively as a herbal product for centuries, contributing to their overexploitation. Health benefits are attributed to their polysaccharide content. We present a comprehensive comparison of the polysaccharide composition of succulent tissues from 93 Aloe species. We found polysaccharide composition primarily related to leaf morphology in alignment with the broad range of Aloe species used medicinally. All aloes except Aloe ferox and Aloe vera are endangered raising concern about over‐harvesting of wild species. Summary Aloes are iconic succulent plants native to Africa, Madagascar and the Arabian Peninsula. All aloes except the commercially grown Aloe ferox and Aloe vera are protected according to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). Major factors contributing to their over‐exploitation are their ornamental value and medicinal use with more than 25% of Aloe species being utilised. The succulent inner leaf mesophyll of aloes is used in traditional medicine, with the healing effect ascribed to the properties of their structural polysaccharides. To explore the correlation between Aloe polysaccharide profiles and other biologically relevant traits across the genus, we (1) extracted polysaccharides and created profiles for nearly 100 representative species using carbohydrate microarrays and molecular probes. We targeted six major plant cell wall polysaccharide groups using 27 different molecular probes. We (2) tested for phylogenetic signal in the polysaccharide profiles and (3) assembled an exhaustive database from literature on the geographic region, level of endemism, altitude, habitat, habit, medicinal use and leaf morphology of the individual species of Aloe. In the absence of phylogenetic signal of polysaccharide profiles, multivariate linear modelling without phylogenetic correction was used and showed that polysaccharide composition primarily correlated with leaf morphology, highlighting the fundamental role of polysaccharides as the building blocks of plants. No correlations between polysaccharide composition of commercial and non‐commercial species were found. We found polysaccharide composition to primarily relate to leaf morphology emphasising the fundamental and structural role of polysaccharides.

Cell wall polysaccharide and glycoprotein content tracks growth‐form diversity and an aridity gradient in the leaf‐succulent genus Crassula

“…This synnovation likely resulted in increased drought resistance and may have fuelled the diversification of Crassula into drier environments in southern Africa (Lu et al, 2022). Moreover, coupled with previous work on storage succulents (i.e., Aloe ; Ahl et al, 2023), the present study also reaffirms the link between glycomics and growth form diversity in succulent lineages.…”

“…This agrees with the RF variable importance plot (Figure S3), which points to pectins and AGPs as the cell wall components driving the distinction between the two Crassula growth forms. Glycomic differences, notably among pectic polysaccharides, have also been reported between growth forms for leaf hydrenchyma of the genus Aloe and its close relatives (Ahl et al, 2023). This reaffirms the link between glycomics (pectins in particular) and growth form diversity in succulent lineages, which has implications for cell wall dynamics and water storage (Fradera‐Soler, Grace, et al, 2022).…”

“…However, despite the alleged importance of cell wall traits in the succulent syndrome, little is known about how such traits vary within a phenotypically diverse lineage of succulent plants. Recent studies have focused on the glycomic diversity of the genus Aloe and its close relatives (Ahl et al, 2023), all of which exhibit storage succulence (Ihlenfeldt, 1985) in their leaves, with distinct achlorophyllous water-storing hydrenchyma. However, the glycomic diversity of all-cell succulents (Ihlenfeldt, 1985) has remained unexplored.…”

The Potential Application of Aloe Barbadensis Mill. as Chinese Medicine for Constipation: Mini-Review

“…Aloe barbadensis Mill., originating from the Arabian Peninsula, was introduced to the island of Curacao in the 16th century by Spanish colonizers. 8 Among the 300 dispersed aloe species worldwide, certain species such as Aloe ferox Mill., Aloe arborescens Mill., and Aloe barbadensis Mill. are recognized as being edible.…”

The legacy of terrestrial plant evolution on cell wall fine structure

“…This success is manifest mainly in terms of morphological and reproductive features (Linder et al, 2018) and indeed the type-II cell wall of grasses is conserved across species from different habitats. This is a testament to its versatility but also raises questions about the degree of dependence of adaptation on cell wall changes, that is, what evolutionary drivers, if any, underlie correlations between cell wall structures and phylogeny (Isager Ahl et al, 2023).…”