The aluminium signal: New dimensions to mechanisms of aluminium tolerance

Bennet, R. J.; Breen, C. M.

doi:10.1007/bf00010728

Cited by 87 publications

(45 citation statements)

References 102 publications

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“…Both the Ca chelator EGTA (ethyleneglycol-bis-(aminomethylether)A^,A^,A'^',A'^'-tetraacetic acid; Bennet & Bandu, 1989) and Al (Bennet, Breen & Fey, 1985) disrupt the secretory function of the peripheral cap cells. Bennet & Breen (1991) suggested that these observations were consistent with a primary response to Al occurring through competition between Al and Ca for sites external to the plasmalemma. Calcium chelating agents, such as EDTA and EGTA, have been shown to inhibit root hair formation (Cormack, 1959(2, b;Jaunin & Hofer, 1988), suggesting a comparable disruption in the function of Ca.…”

Section: Dj Brady and Otherssupporting

confidence: 61%

Calcium amelioration of aluminium toxicity effects on root hair development in soybean [Glycine max (L.) Merr.]

et al. 1993

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SUMMARYLow activities of the monomeric aluminium (Al) species, AP+, AKOH)^" and A1(OH)2+ in solution reduce root growth and root hair development in soybean [Glycine max (L.) Merr.]. Calcium (Ca) ameliorates to a certain extent the toxic effects of Al on root growth, but the interactive effects of Ca and Al on root hair development are not known. In the absence of added Al in solution culture, Ca concentration over the range 500-2000 //M had little effect on root growth or root hair development of soybean cv. Fitzroy. Where the sum of the activities of the monomeric Al species was 2 //M, taproot elongation and lateral root development of soybean was suppressed in solution with 500 //M Ca. The length of the root hair zone was only 10% of that in plants not exposed to Al, and scanning electron microscopy revealed a low density of root hairs. Increasing the Ca concentration to 2000 fiM largely overcame these deleterious effects. The results are discussed in relation to the role of root hairs as infection sites for Bradyrhizobium, and the known effects of Al in suppressing nodulation in soybean.

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Section: Dj Brady and Otherssupporting

confidence: 61%

Calcium amelioration of aluminium toxicity effects on root hair development in soybean [Glycine max (L.) Merr.]

et al. 1993

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“…When Al is selectively applied to the elongation zone or to all of the root except the apex, growth is unaffected (Ryan et al, 1993). Bennet and Breen (1991) described a number of changes to the ultrastructure of cap cells in maize roots after a 2-h treatment with Al and suggested that Al might inhibit root growth indirectly, via a signal-response pathway involving the root cap, hormones, and secondary messengers. This was an attractive hypothesis and consistent with the known involvement of the root cap in signal perception and hormone distribution.…”

Section: Root Apices Are a Target For Al Toxicitymentioning

confidence: 99%

Aluminum Toxicity and Tolerance in Plants

Delhaize

Ryan²

1995

Plant Physiol.

1,134

624

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Aluminum (Al) is the most abundant metal in the earths crust, comprising about 7% of its mass. Since many plant species are sensitive to micromolar concentrations of Al, the potential for soils to be A1 toxic is considerable. Fortunately, most of the A1 is bound by ligands or occurs in other nonphytotoxic forms such as aluminosilicates and precipitates. However, solubilization of this A1 is enhanced by low pH and A1 toxicity is a major factor limiting plant production on acid soils. Soil acidification can develop naturally when basic cations are leached from soils, but it can be accelerated by some farming practices and by acid rain (Kennedy, 1986). Strategies to maintain production on these soils include the application of lime to raise the soil pH and the use of plants that are tolerant of acid soils. Although A1 toxicity has been identified as a problem of acid soils for over 70 years, our knowledge about the primary sites of toxicity and the chain of events that finally affects plant growth remains largely speculative. In this paper we review recent progress that has been made in our understanding of A1 toxicity and the mechanisms of A1 tolerance in plants. ALUMINUM TOXlClTYThe most easily recognized symptom of A1 toxicity is the inhibition of root growth, and this has become a widely accepted measure of A1 stress in plants. In simple nutrient solutions micromolar concentrations of A1 can begin to inhibit root growth within 60 min. However, the inhibition of growth per se offers little information about the causes of stress that will either precede or coincide with changes in growth. To understand the mechanisms of A1 toxicity, it is essential to identify the primary sites involved, both anatomical and metabolic, being mindful that A1 could have diverse effects and act differently in different species. Severa1 reviews on AI toxicity are available (see Haug, 1984;Taylor, 1988; Rengel, 1992a); here we limit our discussion to the sites of A1 toxicity in higher plants and to the possible role of Ca in the primary mechanism of A1 toxicity.The Phytotoxic Form of AI Part of the difficulty of studying Al-related processes in plants can be attributed to the complex chemistry of A1 * Corresponding author; e-mail manny@pican.pi.csiro.au; fax 61-6-246-5000. 315 (Martin, 1988;Kinraide, 1991). A1 hydrolyzes in solution such that the trivalent A1 species, A13+, dominates in acid conditions (pH < 5), whereas the A1(OH)2+ and Al(OH)2+ species form as the pH increases. At near-neutra1 pH the solid phase Al(OH),, or gibbsite, occurs, whereas Al(OH),-, or aluminate, dominates in alkaline conditions. Many of these monomeric A1 cations bind to various organic and inorganic ligands such as POb-, S02-, F-, organic acids, proteins, and lipids. Equilibrium constants are available for many of these reactions and these can be used to predict the relative concentrations of the monomeric A1 species and other A1 compounds in solution. A very toxic polynuclear A1 species, Al,,, can also form when A1 solutions are partially neutralized with...

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“…In roots, one of the primary sites of Al toxicity is the meristems (4,8,9,13). Thus, if the differential Al sensitivity among wheat cultivars is due to a differential Al accumulation in the meristems, then the meristematic tissue of a sensitive cultivar will accumulate more Al than the tissue of a tolerant cultivar.…”

mentioning

confidence: 99%

Aluminum Partitioning in Intact Roots of Aluminum-Tolerant and Aluminum-Sensitive Wheat (Triticum aestivum L.) Cultivars

Rincón¹,

Gonzales²

1992

Plant Physiol.

166

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Aluminum (Al) partitioning in intact roots of wheat (Triticum aestivum L.) cultivars that differ in sensitivity to Al was investigated. Roots of intact seedlings were exposed to Al for up to 24 hours and distribution of Al was assessed visually by hematoxylin staining or by direct measurement of concentration of Al by atomic absorption spectrophotometry or ion chromatography. Major differences in Al accumulation between Al-tolerant (Atlas 66) and Al-sensitive (Tam 105) cultivars were found in the growing regions 0 to 2 and 2 to 5 millimeters from the root apex. Al content was 9 to 13 times greater in the 0 to 2 millimeters root tips of cv Tam 105 than in the tips of cv Atlas 66 when exposed to 50 micromolar Al for 19 to 24 hours. The oxidative phosphorylation inhibitor carbonyl cyanide m-chlorophenylhydrazone and the protein synthesis inhibitor cycloheximide increased Al uptake by intact root tips of cv Atlas 66. Also, loss of Al from the roots of both cultivars was measured after the roots were "pulsed" with 50 micromolar Al for 2 hours and then placed in an Al-free nutrient solution for 6 hours. The 0 to 2 millimeter root tips of cv Tam 105 lost 30% of the absorbed Al, whereas the tips of cv Atlas 66 lost 60%. In light of these results, we conclude that the differential Al sensitivity in wheat correlates with the concentration of Al in the root meristems. The data support the hypothesis that part of the mechanism for Al tolerance in wheat is based on a metabolism-dependent exclusion of Al from the sensitive meristems.

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The aluminium signal: New dimensions to mechanisms of aluminium tolerance

Cited by 87 publications

References 102 publications

Calcium amelioration of aluminium toxicity effects on root hair development in soybean [Glycine max (L.) Merr.]

Calcium amelioration of aluminium toxicity effects on root hair development in soybean [Glycine max (L.) Merr.]

Aluminum Toxicity and Tolerance in Plants

Aluminum Partitioning in Intact Roots of Aluminum-Tolerant and Aluminum-Sensitive Wheat (Triticum aestivum L.) Cultivars

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