Understanding the boron transport network in plants

Abstract

Boron is an essential nutrient for plants and has a largely structural role in development. Globally, there are large tracts of arable land that are deficient in boron, and others where plant growth is restricted by high and toxic boron concentrations. Plants have evolved a range of strategies to cope with deficiency and excess, and considerable genotypic variation exists in responses to variable boron supply. Boron is available to plants as boric acid, a small molecule with a high membrane permeability compared to other mineral nutrients. As a result, its uptake and distribution in plants can be more difficult to control. This review examines the interconnecting network of processes that are employed by plants to try to achieve optimal growth under conditions where the boron supply may be low, adequate or potentially toxic. The emerging picture of boron movement in plants is of a complex multi-layered system designed to optimise the use of boron over a broad range of concentrations. At the cellular level, plants can switch the direction of boron flow through the polar expression of membrane transporters, while at the whole plant level, integration of xylem and phloem transfer can deliver boron to specific tissues dependent on developmental stage.