Sensitive bioassay to evaluate toxicity of aromatic acids to cucumber seedlings

Abstract

Effects of nine aromatic acids found in cucumber root exudates on the growth of its seedlings were evaluated under sterile or unsterile conditions with or without renewing test nutrient solutions. Under non-renewal conditions, although within 24 h, the decrease was not always pronounced but the concentrations of acids were decreased by microbial decomposition and plant uptake during the bioassay. While under daily renewal of test solutions, where the decline in acid concentration was compensated, all the acids strongly inhibited seedling growth, leaf area development and chlorophyll content. Growth inhibition under renewal conditions was greater than those under non-renewal conditions. The inhibition data were described well by nonlinear, least-square curve-fitting method using the Michaelis-Meuten type equation, which expressed the relationship between the growth inhibition and acid concentration. Among the acids examined, 2,4-dichlorobenzoic acid showed the greatest affinity for cucumber root and was the strongest inhibitor. The bioassay with daily renewal of test solution is a practical and sensitive method for the quantitative evaluation of inhibitory effects of aromatic acids on plant growth.