Elucidation of a diurnal pattern of catechin exudation by Centaurea stoebe

The exudation of secondary metabolites at phytotoxic concentrations has been proposed as a mechanism of invasion for some exotic plant species. Catechin is a natural flavanoid implicated in the potential allelopathic interactions of Centaurea stoebe. However, recent studies have shown that catechin is highly unstable and not likely to accumulate in growing medium at phytotoxic concentrations. All previous studies that investigated the allelopathic potential of catechin assumed a continuous exudation of this compound by C. stoebe. Contrary to this, but similar to many other plant secondary metabolites, we hypothesized that catechin exudation may exhibit a pulsed pattern that could facilitate its transient accumulation. Further, we aimed at optimizing a more sensitive detection technique. We tested the hypothesis by quantifying the diurnal pattern of catechin release by C. stoebe in a hydroponic system. Using sample processing, based on a solid phase extraction technique, and more sensitive fluorescent detection parameters, we were able to quantify catechin in the picomolar range from the growing medium. Catechin exudation exhibited a possible diurnal rhythm with respect to light intensity, with the highest concentration at 6 h after exposure to sunlight. Catechin also was found to undergo a degradation reaction resulting in a transient abundance of pyrocatechol in our system.