FUNCTION AND MECHANISM OF ORGANIC ANION EXUDATION FROM PLANT ROOTS

Abstract

The rhizosphere is the zone of soil immediately surrounding plant roots that is modified by root activity. In this critical zone, plants perceive and respond to their environment. As a consequence of normal growth and development, a large range of organic and inorganic substances are exchanged between the root and soil, which inevitably leads to changes in the biochemical and physical properties of the rhizosphere. Plants also modify their rhizosphere in response to certain environmental signals and stresses. Organic anions are commonly detected in this region, and their exudation from plant roots has now been associated with nutrient deficiencies and inorganic ion stresses. This review summarizes recent developments in the understanding of the function, mechanism, and regulation of organic anion exudation from roots. The benefits that plants derive from the presence of organic anions in the rhizosphere are described and the potential for biotechnology to increase organic anion exudation is highlighted.

Phosphate fertilization and phosphorus forms in an Oxisol under no-till

“…The increase of this fraction deep in the soil and following soybeans may be related to the decomposition of root systems of the previous crops. Thus, mineralization of the root system and low molecular weight organic acids released in this process may compete for adsorption sites in the soil (Ryan and Delhaize, 2001) increasing the P availability at greater depths (Rosolem et al, 2004).…”

Iron deficiency induces changes in riboflavin secretion and the mitochondrial electron transport chain in hairy roots of Hyoscyamus albus

“…In parallel with this change, biochemical changes have been observed, including proton extrusion by the activation of a proton-pump H + -ATPase, thereby reducing soil pH and increasing the solubility of Fe 3+ Waters et al, 2002;Hell and Stephan, 2003;Schmidt, 2003;Santi et al, 2005). Concomitantly, organic acids such as citric and malic acids that act as Fe 3+ -chelators (Ryan et al, 2001;Dakora and Phillips, 2002) are released, chelated Fe 3+ is reduced to Fe 2+ by the action of a membrane-bound Fe 3+ chelate reductase, and then Fe 2+ is transported into cells by a Fe-regulated transporter (Waters et al, 2002;Connolly et al, 2003). To support all these processes directly connected with the enhancement of Fe uptake, a supply of ATP as well as of 5 reducing agents such as NAD(P)H is essential (Zocchi, 2007).…”

The roles of organic anion permeases in aluminium resistance and mineral nutrition

“…Some species release organic anions from their roots in response to P deficiency [2] allowing the plants to exploit poorly-soluble forms of P. Citrate, in particular, increases the availability of P in the soil by replacing inorganic P from insoluble complexes or by displacing it from ligands on the surfaces of soil minerals [2]. Electrophysiological studies on white lupin (Lupinus albus) and Arabidopsis show that citrate efflux is likely to be mediated by anion channels (see [37]).…”

“…This is not unexpected as it is likely that numerous solutions to the problem of Al 3+ toxicity have evolved and organic anions with the capacity to bind Al 3+ represent one ''obvious'' way of detoxifying this toxin. Malate and citrate are common carbon currencies in the biochemistry of living organisms and in many cases it appears that it is not their biosynthesis that is rate limiting for efflux but their transport across the plasma membrane [2]. Less clear is the relationship between the ALMT1 genes of Arabidopsis and wheat which to date represent the only two ALMT genes with established roles in Al 3+ resistance.…”