Simultaneous effects of ferulic andp-coumaric acids on cucumber leaf expansion in split-root experiments

Experiments were conducted to determine how plant responses to mixtures of allelochemicals may change as the proportion of roots in contact with allelochemicals is modified. Thirteen-day-old cucumber seedlings were treated with ferulic and/orp-coumaric acid in a split-root nutrient culture system. Leaf areas were determined just prior to treatment and at harvest, 24 hr after treatment. Ferulic acid was more inhibitory to cucumber leaf expansion thanp-coumaric acid. The effects of ferulic andp-coumaric acids on leaf expansion were additive. For individual acids, mixtures of ferulic andp-coumaric acids in the same container and combinations of ferulic andp-coumaric acids in separate containers, the inhibition of leaf expansion was directly related to the product of the concentration of the acid(s) and the proportion of roots treated with the acid(s). Pretreatment with 0.2 or 0.4 mM ferulic acid and subsequent treatment with 0.5 mM ferulic acid failed to show evidence of acclimation by cucumber seedlings.