Can Aquatic Plant Turions Serve as a Source of Arabinogalactans? Immunohistochemical Detection of AGPs in Turion Cells

Turions (overwintering buds) as modified shoot apices constitute specialized vegetative structures that enable many aquatic vascular plants to withstand adverse environmental conditions such as low temperature, desiccation, or limited light availability. Turions serve as major storage sites for organic reserves, including sugars, proteins, fatty acids, and polyamines. Owing to their high content of energy-rich and nutritionally valuable compounds, turions represent a potential renewable resource for applications in biofuel production, animal feed, and the food industry. We investigated whether arabinogalactan proteins (AGPs) occur in aquatic plant turions and localized these compounds within specific tissues or cell types. This work was designed to evaluate whether stress-resistant storage organs may constitute a practical reservoir of AGPs. Considering the central role of AGPs in plant responses to abiotic stress, we hypothesized that turions, which routinely encounter cold, anoxia, and intermittent dehydration, would exhibit particularly high AGP accumulation. Mature turions of aquatic species (<i>Aldrovanda vesiculosa</i>, <i>Utricularia australis</i>, <i>U. intermedia</i>, and <i>Caldesia parnassifolia</i>) were used. Immunofluorescent labeling with AGP-specific antibodies (JIM8, JIM13, JIM14, LM2, MAC207) and confocal laser scanning microscopy were employed. In <i>Aldrovanda vesiculosa</i> and <i>Caldesia parnassifolia</i>, AGP epitopes were abundantly presented in cytoplasmic compartments. AGP epitopes occurred in secretory structures in turions of all examined species (trichomes of <i>Aldrovanda</i> and <i>Utricularia</i>, secretory ducts of <i>Caldesia</i>). In analyzing turions of four different species, we identified <i>Aldrovanda vesiculosa</i> turions as the most promising potential source of AGPs, also noting their high reserve potential for use in animal feed or the food industry.