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    of incoming ultraviolet UV radiation in cucumbers and maize effectively acting as UV shieldsCaldwell M M R Robberecht and S D Flint  Internal filters prospects for UVacclimation in higher plants Physiologia Plantarum     Additionally some allelochemicals act as storage compounds for essential plant nutrients such as nitrogen and phosphorusMcKey D  Adaptive patterns in alkaloid physiology The American Naturalist    Sorry I had meant to move it here but forgot I couldnt find any good place to put it But feel free to add it back if you know where it should go