ARS | Publication request: Secondary metabolite profiles in HLB-affected sweet orange leaves

Submitted to: Subtropical Technology Conference Proceedings
Publication Type: Abstract
Publication Acceptance Date: October 1, 2008
Publication Date: October 16, 2008
Citation: Manthey, J.A. 2008. Secondary metabolite profiles in HLB-affected sweet orange leaves. Subtropical Technology Conference Proceedings. 59:34.

Technical Abstract: Preliminary analyses of methanolic extracts of orange leaves that are either healthy or symptomatic of citrus greening (HLB) have shown consistent differences in the profiles of important classes of phytochemicals. The main flavonoids in symptomatic and healthy leaves were monitored in the HPLC chromatograms at 330 nm, and significant differences were detected in certain hydroxycinnamates and flavone glycosides. In the symptomatic Valencia and Midsweet orange leaves the concentrations of a number of the hydroxycinnamates were nearly twice as high as in the healthy leaves. In contrast, the concentrations of most of the main apigenin glycosides were much lower in the HLB-symptomatic leaves. The main flavanone glycosides were relatively unaffected. Other differences were detected in the Total-Ion-Currents (TICs) of the HPLC-mass spectral analyses of the leaf extracts. Limonin glucoside was substantially higher in the symptomatic leaves compared to the healthy leaves for both sweet orange varieties. Another main difference was the elevated concentration of a compound with a m/z of 187 amu, which was also visualized as an Ehrlich reagent positive band in normal phase TLC of symptomatic leaf extracts. Ehrlich reagent is useful for the detection of limonoids, as well as secondary amines, including alkaloids. The detection by the Ehrlich reagent and the molecular weight suggest that this compound may contain an odd number of N atoms (an alkaloid). The changes detected in the symptomatic fruit have now been compared to the changes in the profiles of compounds in healthy and symptomatic juice of Hamlin and Valencia oranges.