Benzoxazinoids are defense compounds produced by cereals such as rye, wheat, and maize. They are stored in the plants as inactive glucosides, and upon damage to the plant they are hydrolyzed enzymatically into bioactive aglucones. In maize the major compounds are the glucoside DIMBOA-glc and the corresponding aglucone DIMBOA, which is formed by its enzymatic hydrolysis. The aglucone DIMBOA in turn degrades spontaneously into the benzoxazolinone MBOA in an aqueous environment. Benzoxazinoids may also be released into the root zone. Silicone tube microextraction is a sampling technique relying on the diffusion of sufficiently nonpolar compounds from the surroundings into the tubing walls, from where they may be extracted by passing solvent through the tubing. We constructed thin boxes of acrylic material and divided them into eight zones with separate coils of silicone tubing, filled the boxes with vermiculite and water, and grew maize seedlings in them for two weeks. Every three days, methanol was passed through the tubing to extract MBOA exuded from the maize roots before quantitation by LC-MS. In this way we were able to track the MBOA concentration at different depths under the maize seedlings throughout the experiment without disturbing the contents of the boxes. Additionally, root growth was measured by photographing the boxes, tracing the roots, and counting the number of pixels covered by the trace. The MBOA concentration tended to increase first in the upper layer and subsequently in lower layers, with the concentration in the upper layer plateauing. The MBOA concentration correlated roughly with the root growth. Although the method remains to be fully developed, the results suggest that it may be used to monitor benzoxazinoid root exudations from cereals in laboratory experiments because polar precursors degrade into nonpolar compounds that may be reliably sampled.

Sampling of 6-methoxybenzoxazolin-2-one (MBOA) from maize seedlings by silicone tube microextraction

255th National Meeting (2018)

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