Adaptations of Plants to Metal/Salt Contained Environments: Glandlar Structure and Salt Excretion

Abstract

A quantitative assessment was made of metal contamination levels and salinization of Kyzylkum Deserts territories and an analysis of plant/soil samples were investigated in relation to the natural cellular mechanism of plant adaptations to environmental agro-industrial pollutants. Preliminary results provide strong evidence that tailing sands and wet-marsh lands polluted with cadmium, copper, iron, nickel, manganese, chromium, strontium, lead, zinc, various toxic salts and organic pollutants are first colonized by plant species that develop strategies for avoidance and/or tolerance to toxic metals. Our analyses show that the native desert plants, grown on the metalliferous and/or salinized soils tend to accumulate the highest ions concentrations in epidermal and subepidermal tissues, as well as in water bearing parenchyma, including various glandular structures of bracts/bracteoles and perianth segments. A specific adaptive defending strategy by reproductive organs occurred between the vegetative and reproductive functional systems of the resistant plants that ensure them successful sexual reproduction and seed germination. In Chenopods like in some species of Poaceae, glandular structures are usually bicellular, comprising a basal and cap cell, and are referred to as salt glands, trichomes or microhairs. Salt secretion is considered as an adaptive strategy to regulate plant tissue ion concentration. We suggest that the different appearance of the glandular structures in some chenopods and graminous species of Kyzylkum flora is due to differences in their function connected both with accumulation of various ions and /or secretory process. The prismatic crystals secreted by epidermal salt glands and analyzed by X-ray absorption spectrometry contain primarily cations Na, K, Ca, and anions Cl, SO4, carbonate, although other ions such as Mg, Si, and Sr also were detected. Structurally, SEM methods also revealed a high diversity in the micromorphology of epicuticular wax (epicuticular secretion) and silicon deposits that was mostly peculiar for perennial Salsola and gramineous species. The natural plant-cellular mechanism of salt/metal tolerance observed in this study should permit the development and testing of more informed hypotheses regarding adaptations required for colonization and survival of plants, growing under extremely harsh arid and, simultaneously metaliferous/salinized environments. Phytoremediation technology is considered a potentially valuable technique for dealing with heavy metals, which are the most difficult pollutants to remove from soils.