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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.

Fructans isolated from Agave americana grown in South Africa are currently used for spirit production. Structural studies on water-soluble fructans were performed to facilitate the development of other applications including its use as a prebiotic. Acid hydrolysis followed by HPAEC-PAD analysis confirmed that the fructan was composed of glucose and fructose, and size analysis by HPAEC-PAD and size exclusion chromatography indicated that the saccharides have a DP range from 6 to 50. An average DP of 14 was estimated by (1)H NMR analysis. Linkage analysis and ESI-MS studies suggest that A. americana has a neofructan structure consisting of a central sucrose to which (2 → 1)- and (2 → 6)-linked β-D-Fruf chains are attached. The (2 → 1)-linked units extend from C-1 of Fru and C-6 of glucose, whereas the (2 → 6)-linked β-D-Fruf units are attached to C-6 of the central Fru. This structure accounts for the presence of equimolar amounts of 1,6-linked Glu and 1,2,6-linked Fru found in linkage analysis and the multiplicity of the NMR signals observed. Detailed ESI-MS studies were performed on fructan fractions: native, periodate oxidized/reduced, and permethylated oligomers. These derivatizations introduced mass differences between Glc and Fru following oxidation and between 1,2-, 1,6-, 2,6-, and 1,2,6-linked units after methylation. Thus, ESI-MS showed the presence of a single Glc per fructan chain and that it is predominantly internal, rather than terminal as found in inulin. These structural features were confirmed by the use of 1D and 2D NMR experiments.

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