Siri Caspersen

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 material 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 factorial experiments. Root and shoot growth was impeded when 200 μM trans-FA was added to the nutrient solution and the light intensity was in the range of 250–380 μmol m-2 s-1. Root growth showed a stronger response to FA than did shoot growth. At 200 μM, FA strongly inhibited root hair formation and reduced mean lengths of primary, secondary and tertiary roots, but stimulated primary and secondary root branching. Both isomerization to the cis isomer and the presence of the plant reduced the concentration of trans-FA in the nutrient solution during the two weeks exposure period. A third experiment was conducted to assess the influence of irradiance on the phytotoxicity of FA. At a light intensity of 489 μmol m-2 s-1, or in the presence of microorganisms, the concentration of FA in the nutrient solution was lowered and the phytotoxic effects were reduced.

Bacterial amelioration of ferulic acid toxicity to hydroponically grown lettuce (Lactuca sativa L.)

Ferulic acid (FA) is released from plant roots and by decomposition of plant residues and may be involved in allelopathic interactions. We isolated bacteria from the recirculating nutrient solution of a closed, hydroponic lettuce culture using nutrient media supplemented with 1.0 mM FA. The isolates were tested for their capacity to degrade FA in concentrations up to 200 μM. Isolates p208, p210 and p307 showed the highest degradation rates and were therefore used for single- and multiple-strain inoculation in two factorial experiments where lettuce (Lactuca sativa L. cv. Grand Rapids) plants were grown gnotobiotically for 2 weeks in nutrient solution with or without 200 μM FA. When isolate p208 or multiple strains were added, no FA was detectable at the end of the experiments. In the absence of FA, no significant effects of the bacterial treatments could be found with respect to plant dry weight. However, in the presence of FA, isolate p210 increased shoot dry weight and the multiple-strain treatment increased root and shoot dry weights in the first experiment. In the second experiment, isolate p210 neither affected the concentration of FA nor plant dry weights. Isolate p208 and the multiple-strain treatment reduced the negative effect of FA on lateral root lengths and root hair formation in both experiments. Finally, we conclude that bacteria with the capacity to degrade FA and to ameliorate phytotoxic effects of FA were present in the nutrient solution of a commercial hydroponic lettuce culture.