We examined whether allelochemical stress leads to increased lipoxygenase activity in roots of sweet maize (Zea mays L. ssp. saccharata), pea (Pisum sativum L.) and radish (Raphanus sativum L. var. radicula). The lipoxygenase activity of soluble and membrane-bound fractions was assessed in roots after exposure to ferulic and p-coumaric acids. Lipid peroxidation and membrane injury were determined as indicators of stress. Increased lipoxygenase activity of both studied fractions was followed by lipid peroxidation and plasma membrane injury. The results suggest the key role of lipoxygenase in plasma membrane injury during allelochemical stress caused by administration of hydroxycinnamic acids.
This study examined the effects of UV-B radiation and allelochemical stress induced by ferulic acid (FA) on the activity of phenylalanine ammonia lyase (PAL; EC 126.96.36.199) at metabolic and molecular levels in two cucumber genotypes differing in tolerance to cold and disease, in order to determine any interaction between stress effects and genotype response. Stresses were applied simultaneously, sequentially, and singly. In both genotypes, several days of UV radiation retarded growth up to 36%. The effect of FA was not significant. The response to a particular stress, including the effect on PAL activation, was enhanced by simultaneous application of the two stresses. PAL transcription was not correlated with the increase of PAL activity. Exposure to UV-B, FA, and combined UV-B and FA was detrimental to both genotypes but to different extents. The response was not correlated with the genotype of cold and disease sensitivity. PAL activity and its transcription seem to be involved in UV and allelochemical stress, but not related to the plants' tolerance of these stresses.