Carotenoid extraction and analysis using reversed-phase high-performance liquid chromatography (RP-HPLC) was conducted as previously described (Paine et al., 2005 ; Liu et al., 2007 (link)). For the calli, a 0.2 g homogeneous lyophilized sample was extracted. Because of the abundant carotenoid esters in citrus fruits, the extracts from 0.3 g of lyophilized flavedos were saponified with 15% (w/v) KOH:methanol. The RP-HPLC analysis was performed in a Waters liquid chromatography system equipped with a model 600E solvent delivery system, a model 2996 photodiode array detection (PAD) system, a model 717 plus autosampler and an Empower chromatography manager. A C30 carotenoid column (150×4.6 mm; YMC, Japan) was used to elute the carotenoids. The carotenoids were identified by their characteristic absorption spectra and typical retention time based on the literature and standards from CaroNature Co. (Bern, Switzerland). The quantification of the carotenoids was achieved using calibration curves for standards including violaxanthin, lutein, phytoene, α-carotene, β-carotene, β-cryptoxanthin, and lycopene; phytofluene was quantified as phytoene, and α-cryptoxanthin was quantified as β-cryptoxanthin.