Peroxidase activity and lignification in soybean root growth-inhibition by juglone

The changes in activities of soluble and cell wall-bound peroxidases and lignin contents in juglone-stressed soybean (Glycine max) seedlings and their relationships with root growth were investigated. Soybean seedlings (3-d-old) were cultivated in nutrient solution supplemented with 0.5 to 25 mu M juglone for 24 h. Length and dry mass of roots decreased after 5 to 25 mu M juglone treatments. Low juglone concentrations (<= 1 mu M) increased soluble peroxidase activity, while high concentrations (>= 10 mu M) inhibited activities of soluble and cell wall-bound peroxidases. Juglone (<= 1 mu M) did not affect lignin content but highly increased lignification after 5 to 25 mu M treatments. Results indicate that lignification may be an important step in root growth reduction of juglone-stressed soybean.