I think that this is the bit you are talk about:
There are several alternative explanations for the presence of allelochemicals in plants. Evidence suggest that flavonoids and cuticle waxes absorb between 90 – 99% of incoming ultraviolet (UV) radiation in cucumbers and maize, effectively acting as UV shields.Caldwell, M. M., R. Robberecht, and S. D. Flint. 1983. Internal filters: prospects for UV-acclimation in higher plants. Physiologia Plantarum 58:445 – 450.  Additionally, some allelochemicals act as storage compounds for essential plant nutrients such as nitrogen and phosphorus.McKey, D. 1974. Adaptive patterns in alkaloid physiology. The American Naturalist 108:305 - 320.
Sorry, I had meant to move it here, but forgot. I couldn't find any good place to put it. But feel free to add it back, if you know where it should go.