Effects Of Cultural Condition Alterations On Carotenoids Biosynthesis In Embryogenic Callus Of Citrus

Citrus fruits are rich in carotenoids, a group of functional substances. To characterize carotenoids biosynthesis has significant meaning for genetic improvement in citrus.Carotenoids also existed in citrus callus which was an ideal material for studying on regulation of carotenoids biosynthsis. In this paper, we investigated the accumulation of carotenoids in different species citrus callus under different treatments (light qualities, exogenous sugar, herbicide etc.). The results might reveal some external regulators effected in carotenoid biosynthetic pathway.Carotenoids in 34 different citrus species callus were identified and determined by high performance liquid chromatography. All above callus expect those of red tangerine×trifoliate synthesis carotenoids. The main carotenoids were violaxanthin, 9-z-violaxanthin, antheraxanthin, lutein,α-carotene,β-carotene,β-citraurin and phytoene.The vigour of callus was investigated and thaught to be last for 30 ds, then another subculture cycle is needed. After subcultured for 0 d to 20 d, callus grew rapidly, and then tend to aging on 30 d.Sucrose, glucose and fructose presented a decreasing trend in a subculture cycle, glucose and fructose decreased to the minimum in 30 d, and sucrose almost exhausted; Two main organic acids, citric acid and malic acid were detected in callus. In a subculture cycle, accmunication of organic acids changed with callus growth state.Carotenoids profile varied during a subculture cycle. In 'Red Mursh' grapefruit, phytoene,β-carotene and lutein increased to the maximum after subcultured for 10 d, then trend to decreased. Antheraxanthin and lutein increased to its maximum concentration on 10 d or 20 d after subculture, decreased to minimum on 30 d. However,α-carotene kept stable through out the subcultural cycle.In certain extent (concentration of sucrose in the medium from 20 g/L-80 g/L),low concentration of sucrose in the medium inhibited the growth of callus, but promoted the accumulation of carotenoids. As adding sucrose in the medium, the soluble sugar and organic acid content increased correspondingly. Light-dark treatment had no significantly effect on callus growth, carotenoids biosynthesis, soluble sugar and organic content. Dark culture beneficial to callus growth (callus uneasily browning) and promoted the accumulation ofβ-carotene. Dark inhibited biosynthesis of phytoene in Tarrocco blood orange and the inhibition was stronger than in 'Red Marsh'. Light and dark culture had less affect on soluble sugar and organic acids content.Light quality showed a complex effect on carotenoid biosynthesis. It closely related with the callus growth state, external conditions (eg. Temperature etc.), and the duration of dark culture after treatment. Red light promoted carotenoids biosynthesis mostly; Blue light had less effect on the carotenoids biosynthesis. Both red and blue light inhibited organic acid accumulation and had less effect on soluble sugar.After the CPTA treatment, the total carotenoids content in callus increased significantly, upstream carotenoids biosynthesis were promoted, while downstream carotenoids were inhibited. As well, several new carotenoids were produced, such as phytoene andδ-carotene et al. CPTA promoted the transformation of sugar into glucose and fructose, inhibited biosynthesis of organic acid in callus at the same time.