Zinc Absorption from Hydroponic Solutions by Plant Roots

Abstract

Zinc is an essential micronutrient that enters the plant primarily via absorption of Zn²⁺ from the soil solution by plant roots. As with the other micronutrients (except iron), there have been relatively few studies in the literature detailing the mechanism(s) and regulation of Zn²⁺ absorption by plant roots. Much of the research in the literature has been based on solution culture techniques; in this paper, the current literature pertaining to root Zn²⁺ absorption is reviewed, and speculative models for the mechanisms of Zn²⁺ uptake are presented. The possibility that phytosiderophores, which are low-molecular weight organic molecules that complex iron and are released by roots, play a significant role in Zn²⁺ absorption in grasses is discussed. For dicots and non-graminaceous monocots, a speculative model is presented whereby Zn²⁺ influx into root cells is mediated by a divalent cation channel. In this model, gating of the channel is influenced by the activity of the plasma membrane reductase involved in ferric reduction, that has recently been shown to be induced by the imposition of micronutrient deficiencies other than Fe (including Zn).