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Saltbush seedlings (Atriplex spp.) shed border-like cells from closed-type root apical meristems

Alison Gill , Rachel Burton

Abstract

Australian saltbush species survive in exceptionally saline environments and are often used for pasture in semi-arid areas. To investigate the impact of salinity on saltbush root morphology and root exudates, three Australian native saltbush species (Atriplex nummularia, A. amnicola and A. vesicaria) were grown in vitro in optimised sterile, semi-hydroponic systems in media supplemented with different concentrations of NaCl. Histological stains and chromatographic techniques were used to characterise the root apical meristem (RAM) type and root exudate composition of the saltbush seedlings. We report that saltbush species have closed-type RAMs from which border-like cells (BLCs) are released. Monosaccharide content, including glucose and fructose, in the root mucilage of saltbush was found to be uniquely low, suggesting that saltbush may minimise carbon release in polysaccharides of root exudates. Root mucilage also contained notable levels of salt, plus increasing levels of unidentified compounds at peak salinity. Unesterified homogalacturonan, xyloglucan, and arabinogalactan proteins between and on the surface of BLCs may aid intercellular adhesion. At the highest salinity levels, root cap morphology was altered but root:shoot ratio remained consistent. While questions remain about the identity of some components in saltbush root mucilage other than the key monosaccharides, this new information about root cap morphology and cell surface polysaccharides provides avenues for future research.

FP24178  Accepted 04 September 2024

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