Interactive effects of lettuce (Lactuca sativa L.), irradiance, and ferulic acid in axenic, hydroponic culture

Ferulic acid (FA) is released by living roots and by decaying plant materia l and is involved in chemical interactions between plants. Effects of FA on plant growth and root development of lettuce (Lactuca sativa L. cv. Grand Rapids) cultivated in axenic nutrient solution were studied in two factoria l experiments. Root and shoot growth was impeded when 200 mu M trans-FA was added to the nutrient solution and the light intensity was in the range of 250-380 mu mol m(-2) s(-1). Root growth showed a stronger response to FA t han did shoot growth. At 200 mu M, FA strongly inhibited root hair formatio n and reduced mean lengths of primary, secondary and tertiary roots, but st imulated primary and secondary root branching. Both isomerization to the ci s isomer and the presence of the plant reduced the concentration of trans-F A in the nutrient solution during the two weeks exposure period. A third ex periment was conducted to assess the influence of irradiance on the phytoto xicity of FA. At a light intensity of 489 mu mol m(-2) s(-1), or in the pre sence of microorganisms, the concentration of FA in the nutrient solution w as lowered and the phytotoxic effects were reduced.