Ferulic acid interactions and root exudation by hydroponically grown lettuce (Lactuca sativa L.) as influenced by external factors
1997
Caspersen, S. (SLU, Alnarp (Sweden). Inst. foer Traedgaardsvetenskap)
In hydroponic plant production, recirculation of the nutrient solution may reduce water use and the release of waste nutrient solution to the environment. The aim of the present study was to investigate root exudation and effects of potential exudate components on the growth and development of hydroponically cultivated lettuce (Lactuca sativa L.). A hydroponic model system was developed for gnotobiotic studies. Plant dry weights and root release of dissolved organic carbon (DOC) were higher at 100% than at 25 or 50% of the full strength nutrient solution when plants were harvested after three weeks. Reducing the external P concentration from 0.5 to 0.2 mM reduced shoot dry weight and increased the root:shoot ratio, but did not affect root release of DOC significantly. The effects of ferulic acid (FA) on lettuce growth and development were investigated under axenic conditions. At 200 microM FA, root lengths and root hair development decreased, and primary and secondary root branching increased. The reduction of plant growth by 200 microM FA which was observed at light intensities between 250 and 380 m-2s-1 was less pronounced at 490 micromol m-2s-1. At the highest light intensity, the concentration of trans-FA decreased, both due to a higher degree of isomerization to the cis-isomer and to an increased uptake and/or action mediated by the plant. Bacteria were isolated from the nutrient solution of a closed, hydroponic lettuce culture on FA-containing agar media, and were tested for their ability to degrade FA. When applied gnotobiotically in the presence of lettuce plants and 200 microM FA, some of the isolates were able to degrade FA and to reduce the effects of FA on plant dry weight and root development. The effects of different nutrient treatments on FA toxicity were studied under unsterile, hydroponic conditions. The observed interactions between FA and nutrient treatments regarding the nutrient contents of the plants were not reflected in plant dry weights.
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