Transcriptomic and targeted metabolome analyses revealed the regulatory mechanisms of the synthesis of bioactive compounds in Citrus grandis 'tomentosa'.

Exocarpium Citri Grandis is a popular Chinese herbal medicine prepared from Citrus grandis 'tomentosa', and it is rich in several bioactive compounds, including flavonoids, coumarins, and volatile oils. However, studies are yet to elucidate the mechanisms of synthesis and regulation of these active components. Therefore, the present study examined the profiles of flavonoids and volatile oil bioactive compounds in plant petals, fruits, and tender leaves, and then performed RNA sequencing on different tissues to identify putative genes involved in the synthesis of bioactive compounds. The results show that the naringin, naringenin, and coumarin contents of the fruitlets were significantly higher than those of the tender leaves and petals, whereas the tender leaves had significantly higher levels of rhoifolin and apigenin. A total of 49 volatile oils, of which 10 were mainly found in flowers, 15 were mainly found in fruits, and 18 were mainly found in leaves, were identified. RNA sequencing identified 9,942 genes that were differentially expressed in different tissues. Further analysis showed that 20, 15, and 74 differentially expressed genes were involved in regulating flavonoid synthesis, regulating coumarin synthesis, and synthesis and regulation of terpenoids, respectively. CHI1 (Cg7g005600) and 1,2Rhat gene (Cg1g023820) may be involved in the regulation of naringin synthesis in C. grandis fruits. The HDR (Cg8g006150) gene, HMGS gene (Cg5g009630) and GGPS (Cg1g003650) may be involved in the regulation and synthesis of volatile oils in C. grandis petals. Overall, the findings of the present study enhance our understanding of the regulatory mechanisms of secondary metabolites in C. grandis, which could promote the breeding of C. grandis with desired characteristics.

Fabrication and characterization of hydroxyapatite/sodium alginate/chitosan composite microspheres for drug delivery and bone tissue engineering.

Hydroxyapatite/sodium alginate/chitosan (HA/SA/CS) composite microspheres, which possess good biocompatibility for specific biomedical application, were prepared using an emulsion crosslink technique; calcium ions were used as a cross-linking agent. The effect of the concentration of sodium alginate (SA), the volume ratio of water to oil, the content of hydroxyapatite (HA) nanoparticles, as well as rotation speed, on the morphology and dispersion of composite microspheres were investigated. Also investigated were the drug loading, release behaviors, in vitro hemolysis activity, cytotoxicity, cell adhesion and proliferation capacity of the materials. The results demonstrate that the HA/SA/CS composite microspheres were successfully prepared; their drug loading and encapsulation efficiency are much higher than that of HA nanoparticles. Dox-loaded HA/SA/CS composite microspheres show good pH-sensitive drug-release capability. The hemolysis and cytotoxicity tests suggest that the microspheres have good blood and cell compatibility. Furthermore, the prepared composite microspheres display better cell adhesion and proliferation capacity than HA nanoparticles and HA/SA composite microspheres. Therefore, the HA/SA/CS composite microspheres might have potential as drug carriers in a pH-responsive controlled-release drug delivery system and as candidates for application in bone tissue engineering.