| Cara Cara navel orange is a bud mutation from the Washington navel orange, its peculiar pink pulp coloration is due to lycopene accumulation. As a member of carotenoids, lycopene is also derivated from terpenoids pathway. Compared with yellow-fleshed Seike navel orange, content changes of terpenoids such as carotenoids, limonoids, ABA, and related contents changes of soluble sugar, organic acid and expression of carotenogenic genes during the fruits development in two succeed seasons were analyzed. In addition, cDNA microarray was performed to decipher the differences. The results could help us get more knowledge on the mechanism involved in the formation of red-fleshed trait in citrus fruit. The main results were as follows:1. The composition and content changes of carotenoids in different fruit tissues of Cara Cara and Seike were measured by HPLC. The result showed that total carotenoids were largely increased in Cara Cara, and the compositions were different too. Phytoene, phytofluene and lycopene were dominantly accumulated in Cara Cara, whileβ-carotene,β-cryptoxanthin and violaxanthin were main carotenoids in Seike.2. Real-time RT-PCR analysis revealed that lycopene accumulation in the juice sacs of Cara Cara was related to up-regulated expression of PSY, while was less related with the expression of LCY. However, the expression of PSY was also up regulated in flavedo, whereas lycopene level was not increased. It suggested that the different regulation models were behind lycopene accumulation in juice sacs and flavedo.3. The content of limonin and nomilin were measured during fruit development. Results showed a significant decline tendence of the two limonoids in fruits of two cultivars during fruit development, but the contents of limonin and nomilin were notablely higher in Cara Cara fruits than in Seike in almost all development stages.4. HPLC analysis indicated that ABA were gradually accumulated at early stages of fruit development but decreased rapidly at maturation, while the content of carotenoids reached to the highest value in matrue stage in both cultivars. Through the fruit development, the level of ABA in Cara Cara was always significant lower than in Seike. Correlation analysis showed that the contentss of carotenoids and ABA were negatively related (r=-0.58).5. Gas chromatography analysis revealed that sucrose and citric acid were dominatedly accumulated in the juice sacs of Cara Cara and Seike, while the content was obviously higher in Cara Cara than in Seike. 6. The microarray analysis results showed that 1453 genes of differential expression were screened out. These genes were involved in many metabolic pathways such as carotenoids biosynthesis, isoprenoids biosynthesis, pyruvate metabolism, starch and sucrose metabolism, citrate cycle, and glycolysis pathways, which was coordinate with our biochemical ananlysis. |
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