Salicylic acid-induced changes to growth and phenolic metabolism in Matricaria chamomilla plants

The influence of salicylic acid (SA) doses of 50 and 250 mu M, for a period of up to 7 days, on selected physiological aspects and the phenolic metabolism of Matricaria chamomilla plants was studied. SA exhibited both growth-promoting (50 mu M) and growth-inhibiting (250 mu M) properties, the latter being correlated with decrease of chlorophylls, water content and soluble proteins. In terms of phenolic metabolism, it seems that the higher SA dose has a toxic effect, based on the sharp increase in phenylalanine ammonia-lyase (PAL) activity (24 h after application), which is followed by an increase in total soluble phenolics, lignin accumulation and the majority of the 11 detected phenolic acids. Guaiacol-peroxidase activity was elevated throughout the experiment in 250 mu M SA-treated plants. In turn, some responses can be explained by mechanisms associated with oxidative stress tolerance; these mitigate acute SA stress (which is indicated by an increase in malondialdehyde content). However, PAL activity decreased with prolonged exposure to SA, indicating its inhibition. Accumulation of coumarin-related compounds (umbelliferone and herniarin) was not affected by SA treatments, while (Z)- and (E)-2-beta-D-glucopyranosyloxy-4-methoxycinnamic acids increased in the 250 mu M SA-treated rosettes. Free SA content in the rosettes increased significantly only in the 250 mu M SA treatment, with levels tending to decrease towards the end of the experiment and the opposite trend was observed in the roots.