Changes in citrus leaf flavonoid concentrations resulting from blight-induced zinc-deficiency

Increased flavonoid concentrations were found to correlate with the elevated levels of leaf phenolic compounds occurring in blight-induced zinc-deficient citrus. In orange (Citrus sinensis L.) leaves, the increases occurred primarily in hesperidin and diosmin, whereas in grapefruit (C. paradisi Macf.) the largest increases occurred in naringin and rhoifolin. Zinc-deficiency occurring in the blighted citrus leaves appeared to be the important contributing factor to the increased flavonoid content. Although the leaves from trees with blight were typically smaller than leaves from unaffected trees, the increased flavonoid content was not significantly due to a concentration effect. Large differences occurred in the percent increases in concentrations of certain citrus leaf flavonoids. While large increases occurred for a number of flavanone and flavone glycosides, much smaller percent increases occurred for other minor flavone glycosides, and the polymethoxyflavone aglycones. The parallel increases occurring in the concentrations of certain flavone glycosides and their flavanone analogs provide a further indication that flavanone glycosides are precursors in the biosynthesis of flavone glycosides in citrus.