In vitro evidence of aluminum effects on solution movement through root cell walls

Little is known about the primary effects of aluminum (Al) in reducing root growth. However, the sorption of Al by the root cell wall, particularly by calcium (Ca) pectate, has been suggested as being important in the expression of Al toxicity in plants. To overcome problems arising from the close proximity of root cell components that may react with Al, a synthetic Ca pectate membrane was prepared as a model system for Al studies. Solution containing 1 mM Ca (as CaCl2) was passed through the membrane, and the flow rate measured. Solution containing 29 μM Al (as AlCl3) and 1 mM Ca reduced solution flow rate by > 80% from c. 3.5 to c. 0.6 mL/min within 2 min, with a further slight decline over the next 4 min. The Al concentration in solution proximate to the inlet side of the membrane decreased to 15 μM within 10 min, and only 3 μM Al was measured in solution that had passed through the membrane. These results suggest that an important primary effect of toxic Al is a reduction in water movement into the root, with consequent effects on water relations in the plant.