Carotenoids synthesized in citrus callus of different genotypes

Eight carotenoids, such as phytoene, alpha-carotene, violaxanthin, etc., synthesized in citrus callus of 31 genotypes were identified and determined. Though varied with genotypes, the carotenoids composition of callus derived from a certain genotype was stable, while carotenoids contents altered between sub-cultures. Some specific carotenoids were produced in calluses of limited genotypes: beta-citraurin was only synthesized in calluses of Nianju tangerine (Citrus reticulata Blanco) and Page tangelo (C. reticulata x C. paradisi); while 9-Z-violaxanthin was only detected in Nianju tangerine and Skaggs Bonanza navel orange (C. sinensis L. Osbeck). Notably, the only carotenoid detected in calluses of Natsudaidai (C. aurantium L.) and other two sweet oranges (C. sinensis L. Osbeck) was phytoene. It implied that citrus calluses could be employed to produce specific carotenoids in the future. To further elucidate the characters of callus carotenoids profile, comparisons of carotenoids profiles was made among calluses, fruit tissues and leaves of four selected citrus genotypes. Results showed that lycopene was not detected in leaves and calluses; nevertheless, both citrus fruits and calluses accumulated phytoene, whereas leaves did not except those of Cara Cara navel orange. It is postulated that citrus callus featured its carotenoids profile different from fruit tissues and leaves. In conclusion, the advantages of using citrus callus as an alternative model research system in understanding the regulation of carotenogenesis have been discussed.