Influence of phosphate and hydroxyl ions on aluminum toxicity in sorghum and wheat

• Published in: Journal of plant nutrition Vol. 17; no. 2/3
• Main Authors: Shuman, L.M, Wilson, D.O
• Format: Journal Article
• Language: English
• Published: 1994
• Subjects: ALUMINIO; ALUMINIUM; ANION; ANIONES; CHLORURE DE CALCIUM; CLORURO CALCICO; CRECIMIENTO; CROISSANCE; FITOTOXICIDAD; FOSFORO; NITRATE DE POTASSIUM; NITRATO DE POTASIO; PHOSPHORE; PHYTOTOXICITE; RACINE; RAICES; SOLUCIONES NUTRITIVAS; SOLUTION NUTRITIVE; SORGHUM BICOLOR; TRITICUM AESTIVUM
• ISSN: 0190-4167

Aluminum (Al) toxicity to plants in complete nutrient solutions is difficult to relate to Al activity in solution because of precipitation and complexation. Aluminum toxicity was studied for two seedling crops, sorghum (Sorghum bicolor L. Moench) and wheat (Triticum aestivum L. em Thell), at low levels (less than or equal to 10 micromolar) in two incomplete nutrient solutions to study plant response to Al alone, Al+PO4(3-), Al+OH-, and Al+PO4(3-)+OH-. Relative root length was the bioassay for Al toxicity. 'Monomeric' Al was measured using Aluminon and both root length and measured Al were compared to the theoretical Al in solution predicted by the MINTEQA2 equilibrium model. Low levels of Al were toxic to plant roots with sorghum showing a decrease in relative root length from 1 to 10 micromolar Al, and wheat showing a decrease from 4 to 10 micromolar. A mono-salt background solution (400 micromolar CaCl2) and a more complex base solution (CaCl2, KNO3, and MgCl2) gave similar root lengths and measured Al values. Phosphate and hydroxyl ameliorated Al toxicity and lowered measured Al in solution, but not to the extent predicted by the model. Adding phosphate (PO4(3-)) or hydroxyl (OH-) raised the pH, but again not as high as the model predicted. The difference in toxicity and measured Al were most likely the result of polymers (Al(+3)) which are toxic, but not measured by the procedure used, or included in the model which showed the Al as being removed from solution by precipitation