Submitted to: Plant Physiology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 7, 2000
Publication Date: N/A
Interpretive Summary: Citrus blight is a disease that kills nearly a half million trees per year in the state of Florida. Many facets of this disease remain largely unknown, although early studies have shown that elevated levels of certain types of plant compounds occur in the leaves of affected citrus trees. The current study provides new information concerning the chemical changes, pertaining to the important class of compounds termed `flavonoids' that occurs in the leaves of the blight-affected trees. This information provides us with insights into the biosynthesis of these citrus flavonoids, and suggests conditions under which these biosynthetic sequences can be further studied. These compounds play extremely important roles in the citrus industry, both in terms of taste and of health properties. Understanding the biosynthesis of these dietary components of citrus will be useful to the industry in developing new varieties and markets for processed products.
Technical Abstract: The elevated levels of phenolic compounds that occur in leaves of citrus trees affected by blight were shown to be due to increased flavonoid accumulation. In orange (Citrus sinensis L.) leaves these increases occurred primarily in hesperidin and diosmin, whereas in grapefruit (C. paradisi Macf.) the largest increases occurred in the levels of naringin and rhoifolin. The zinc-deficiency that occurred in the blighted citrus leaves was an important contributing factor to the increased flavonoid content. Although the leaves from trees with blight were typically smaller than control, healthy leaves, the increased flavonoid content was not significantly due to a concentration effect in the smaller leaves. Distinct differences occurred in the levels of change in the accumulation of different citrus flavonoids. While there were large increases in the concentrations of certain flavanone and flavone glycosides, much smaller increases occurred in the concentrations of other minor flavone glycosides and in the polymethoxylated flavones. The concurrent increases in the concentrations of the flavone analogs of hesperidin and naringin provide evidence of a close association in the biosynthesis of these flavones from the glycosidated flavanone precursors.