Solid-phase microextraction method for in vivo measurement of allelochemical uptake.

Solid-phase microextraction (SPME) was used to measure allelochemical uptake by tomato plants in vivo. Exogenously applied 1,8-cineole was rapidly taken up by tomato, with the first traces of cineole being detected in the tomato stem just 1-2 h after a single application of 0.5 mM cineole to soil. The pulse of cineole persisted in the tomato stem for 72 h. When cineole concentrations were measured 24 h after a single application, trace amounts of cineole could be detected in tomato stem fluid at application concentrations as low as 50 microM. Tomato was also found to take up camphor, menthol, and coumarin, but not carveol. In preliminary tests with common ragweed (Artemisia annuifolia L.) and purslane (Portulaca oleraceae L.) plants growing in garden beds, both ragweed and purslane took up 1,8-cineole, and purslane also took up camphor. The quantitation of allelochemical uptake by plants is considered to be a crucial test of hypotheses of allelopathic effects, but demonstration of allelochemical uptake has had to be inferred based on observed toxicity due to the lack of methods to measure uptake in vivo. This new technique now provides a means of tracking compounds within target plants. Furthermore, the demonstrated rapid uptake of 1,8-cineole by plants suggests a potential mechanism whereby brief pulses of allelochemicals over an extended period of time might be able to exert an allelopathic effect on plants.