Cation Amelioration of Aluminum Toxicity in Wheat

Abstract

Aluminum is a major constituent of most soils and limits crop productivity in many regions. Amelioration is of theoretical as well as practal interest because understanding amelioration may contribute to an understanding of the mechanisms of toxicity. In the experiments reported here 2-day-old wheat (Triticum aestivum L. cv Tyler) seedlings with 15-millimeter roots were transferred to solutions containing OA millimolar CaC12 at pH 4.3 variously supplemented with AlG3 and additionl amounts of a chloride salt. Root lengths, measured after 2 days in the test solutions, were a function of both Al activity and the cation activity of the added salt. Percent inhibition = 100 JAl3'J/(JAV3J + K, + alCQ') where 1A31+ is the activity of Al' expressed in micromolar, IC) is the activity of the added cation expressed in millimolar, and K. (= 1.2 micromolar) is the JAI'3+ required for 50% inhibition in the absence of added salt. For Ca2+, Mg2, and Na the values of a were 2.4, 1.6, and 0.011, respectively, and the values for v were 1.5, 1. (3,5, 25) describe high correlations between growth reductions and the activity of A13+ or total mononuclear species, but reports supporting a direct ameliorative effect of cations are few.Ca is a well known ameliorant that has been observed many times to relieve Al toxicity (2,3,7,18,26), but in only a few cases have the investigators attempted to demonstrate that some or part of the amelioration can be attributed to one or the other of the effects enumerated above (3, 18). Mg is also an effective ameliorant (2,10,18,26), and a recent study demonstrated that both Ca and Mg salts were much more effective ameliorants of Al toxicity than K and Na salts at comparable ionic strengths (18). Thus, Ca and Mg relieved toxicity beyond that attributable to ionic-strength effects, and a physiological interaction between Al and the cations was indicated. The only report ofamelioration by monovalent cations is the dissertation of Ali (2) who concluded that K and Na were equally ameliorative but less effective than Ca and Mg which were equal to each other.We have undertaken a study of cation amelioration that employs a recently published assay for Al phytotoxicity (18). The advantages of the assay are speed, simplicity, sensitivity to low Al levels, the elimination of nutrient requirements other than Ca, and a good correspondence to other assay procedures. The main advantage is that the simplicity of the basal medium (0.4 mM CaCl2 adjusted to pH 4.3 with HCI) permits a more precise computation of Al speciation than do more complete nutrient media. The objectives of the current study were (a)

Interactive Effects of Al3+, H+, and Other Cations on Root Elongation Considered in Terms of Cell-Surface Electrical Potential

“…competitive) cation inhibition of Al3" binding at a surface ligand whose degree of Al saturation determines the degree of intoxication (10,13). This hypothesis is different than the one considered in the present article.…”

“…In 1987 (13) (20) and other equilibrium constants compiled by Lindsay (17). From that study and other experiments it was determined that the ameliorative effectiveness of cations (at constant IA13+iE) was in the order Ca2+ > Mg2+ _ Sr,+ >> K+ z Na+, but no interpretation from an electrostatic viewpoint was offered.…”

“…At constant IAl3+IE,2 divalent cations ameliorate toxicity much more effectively than do monovalent cations (3,13), but H+ is even more effective than divalent cations. H+ increases of less than 50 ,M in the pH range 4 to 5 were significantly ameliorative for four dicotyledonous plants (15).…”

Fluorescence Resonance Energy Transfer-Sensitized Emission of Yellow Cameleon 3.60 Reveals Root Zone-Specific Calcium Signatures in Arabidopsis in Response to Aluminum and Other Trivalent Cations

“…The shapes of the ATPinduced [Ca 2+ ] cyt signature that we observed were similar to those reported in mammalian cells expressing YC3.60 (Nagai et al, 2004 (Sivaguru and Horst, 1998). Since the toxic species of Al 3+ forms at low pH (Kinraide and Parker, 1987), we prepared a working solution of AlCl 3 in half-strength MS medium at pH 4.5. Application of the low-pH solution alone had no impact on [Ca 2+ ] cytdependent FRET efficiency in cells of the transition zone, but when supplemented with Al 3+ , we observed transient [Ca 2+ ] cyt -dependent FRET efficiency increases (Fig.…”

Plasma Membrane Surface Potential: Dual Effects upon Ion Uptake and Toxicity

“…For our reanalysis, uptake data were taken from the author's tables. For the Zn 2+ uptake experiments, increases in Ca 2+ concentration or decreases in pH resulted in decreases in We reevaluated the Ca 2+ and Mg 2+ alleviation of Al 3+ rhizotoxicity in wheat (cv Tyler) roots from data archived from, but not presented in, a study by Kinraide and Parker (1987). Two-day-old seedlings were transferred to solutions containing 0.4 mM CaCl 2 at pH 4.3 variously supplemented with AlCl 3 and MgCl 2 or additional CaCl 2 .…”