Secondary Metabolite Profiles of Leaves of Healthy and Huanglongbing-infected Orange (Citrus sinensisL.) Seedlings Measured by HPLC-Fluorescence Detection

John A Manthey, Jose Reyes-De-Corcuera, Faraj Hijaz, Svetlana Y Folimonova, Shelley Jones, Craig Davis

Abstract


Leaves of greenhouse-grown ‘Hamlin’ and ‘Valencia’ orange (Citrus sinensis L.) seedlings were analyzed by high performance liquid chromatography in a study of the progression of changes in secondary metabolite profiles resulting from infection by CandidatusLiberibacter asiaticus (CLas), the Huanglongbing causative pathogenic bacterium. Following graft transmission of CLas into the young trees, infection was monitored in new growth by PCR and visual symptoms. Leaves from healthy non-infected trees and from infected trees were analyzed principally for their profiles of fluorescent secondary metabolites. Two distinct profiles of compounds were observed at later collection dates, one predominantly in leaves of non-infected trees, and the other in visually symptomatic infected leaves. Characterizations of these peaks were made using high performance liquid chromatography coupled with photodiode array, fluorescence, and mass spectrometry. These characterizations showed that fluorescent compounds in the orange leaf extracts included polymethoxylated flavones, coumarins, and conjugated hydroxycinnamates, although other unknowns were also detected. The fluorescence detection of these compounds was optimized by measuring the emission and excitation spectra of purified standards of structurally related citrus leaf compounds.


Keywords


CandidatusLiberibacter asiaticus, flavonoid, coumarin, metabolome, biomarker

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283