Organic acid exudation as an aluminum-tolerance mechanism in maize (Zea mays L.)

Abstract

Abstract. In this study, the role of root organic acid synthesis and exudation in the mechanism of aluminum tolerance was examined in Al-tolerant (South American 3) and Al-sensitive (Tuxpefio and South American 5) maize genotypes. In a growth solution containing 6 ~tM A13+, Tuxpefio and South American 5 were found to be twoand threefold more sensitive to A1 than South American 3, Root organic acid content and organic acid exudation from the entire root system into the bulk solution were investigated via high-performance liquid chromatographic analysis while exudates collected separately from the root apex or a mature root region (using a dividedroot-chamber technique) were analyzed with a more-sensitive ion chromatography system. In both the Al-tolerant and Al-sensitive lines, A1 treatment significantly increased the total root content of organic acids, which was likely the result of A1 stress and not the cause of the observed differential A1 tolerance. In the absence of A1, small amounts of citrate were exuded into the solution bathing the roots. Aluminum exposure triggered a stimulation of citrate release in the Al-tolerant but not in the Al-sensitive genotypes; this response was localized to the root apex of the Al-tolerant genotype. Additionally, AI exposure triggered the release of phosphate from the root apex of the Al-tolerant genotype. The same solution A13+ activity that elicited the maximum difference in AI sensitivity between Al-tolerant and Al-sensitive genotypes also triggered maximal citrate release from the root apex of the Al-tolerant line. The significance of citrate as a potential detoxifier for aluminum is discussed. It is concluded that organic acid release by the root apex could be an important aspect of A1 tolerance in maize.

Organic acids produced by mycorrhizal Pinus sylvestris exposed to elevated aluminium and heavy metal concentrations

“…Pellet et al, 1997) and citric acid (Pellet et al, 1995 ;Ma et al, 1997a). The role of malate in Al tolerance may be to inhibit the blocking of the root cell plasma membrane Ca# + channel (Huang et al, 1996).…”

“…Several different organic acids, principally oxalic (Ma et al, 1997b), citric (Pellet et al, 1995 ;Ma et al, 1997a) and malic (e.g. Pellet et al, 1997) acids, have been found to be produced in increased amounts by non-mycorrhizal roots exposed to Al.…”

Organic acids enhance the uptake of lead by wheat roots

“…For example, several studies have shown the key role of organic acids in affecting plant tolerance to aluminum (Pellet et al 1995;Ma et al 2001). The role of organic acids in mediating the uptake of Fe 3+ was ascribed to ferric reductase activity and the presence of cation channels (Schmidt 1999).…”

Aplicaciones de aluminio mantienen el crecimiento de fresa (Fragaria × ananassa Duch.) suplementada con roca fosfórica en condiciones de cultivo sin suelo.

“…El ácido secretado puede variar entre especies, por ejemplo, el ácido málico es secretado por plantas de trigo (Delhaize et al, 1993), el cítrico por frijol (Miyasaka et al, 1991) y maíz (Pellet et al, 1995) y el oxálico por trigo (Zheng et al, 1998b). Es posible también que más de dos tipos de AO puedan ser secretados por una misma planta (Ma, 2000) como ocurre en canola, avena, rábano (Zheng et al, 1998a) y triticale , las cuales secretan tanto ácido málico como ácido cítrico.…”