In plants, the role of anthocyanins trafficking in response to high temperature has been rarely studied, and therefore poorly understood. Red-fleshed kiwifruit has stimulated the world kiwifruit industry owing to its appealing color. However, fruit in warmer climates have been found to have poor flesh coloration, and the factors responsible for this response remain elusive. Partial correlation and regression analysis confirmed that accumulative temperatures above 25 °C (T25) was one of the dominant factors inhibiting anthocyanin accumulation in red-fleshed Actinidia chinensis, 'Hongyang'. Expression of structural genes, AcMRP and AcMYB1 in inner pericarp sampled from the two high altitudes (low temperature area), was notably higher than the low altitude (high temperature area) during fruit coloration. AcMYB1 and structural genes coordinate expression supported the MYB-bHLH (basic helix-loop-helix)-WD40 regulatory complex mediated downregulation of anthocyanin biosynthesis induced by high temperatures in kiwifruit. Moreover, cytological observations using the light and transmission electronic microscopy showed that there were a series of anthocyanic vacuolar inclusion (AVI)-like structures involved in their vacuolization process and dissolution of the pigmented bodies inside cells of fruit inner pericarp. Anthocyanin transport was inhibited by high temperature via retardation of vacuolization or reduction in AIV-like structure formation. Our findings strongly suggested that complex multimechanisms influenced the effects of high temperature on red-fleshed kiwifruit coloration.

Seedlings derived from an Actinidia interspecific cross between the hexaploid Actinidia chinensis var. deliciosa 'Jinkui' and the diploid male A. eriantha 9 A. chinensis var. chinensis 'Chaohong' hybrid were analyzed using flow cytometry, SSR markers and phenotypic observations. The results show that the leaf vitamin C content of this hybrid population has a mid-parent heterosis. Separation of flower color in the progeny was also observed, progeny with red flowers lighter than 'Chaohong', white flowers as in 'Jinkui' and intermediate types with a red base to the petals and white margins were all present. Flow cytometry analysis confirmed that most of the progeny were tetraploids, and molecular marker data showed that most of these tetraploid progeny had three alleles from the hexaploid parent and one allele from the diploid parent. UPGMA analysis based on the SSR markers showed that the diploid parent was completely separated from the hexaploid parent and all the progeny.

This study investigated the flavonoid compounds in Actinidia chinensis and Actinidia arguta fruits. A total of 125 flavonoids, including 9 anthocyanins, 12 catechins, 17 flavanones, 48 flavones (including 14 flavone C-glycosides), 29 flavonols, 6 isoflavones, and 4 proanthocyanidins, were identified in "Hongyang" kiwifruit (red flesh), "Jintao" kiwifruit, "Mini Amethyst" kiwiberry (purple flesh), and "Kuilv" kiwiberry. Thirty-nine metabolites showed significantly different contents between "Hongyang" and "Jintao," and 38 of them showed higher content in "Hongyang," whereas 39 metabolites showed significantly different contents between "Mini Amethyst" and "Kuilv," and 31 of them showed higher content in "Mini Amethyst." This result indicates the superior nutritional value of the pigmented kiwi cultivars in terms of flavonoids. Multivariate statistical analysis indicates that the variation in flavonoid profiles contributes to the pigmentation phenotypes of "Hongyang" and "Mini Amethyst." Further comparative transcriptomic analysis revealed that structural genes in the anthocyanin synthesis pathway (AcF3H, AcF3′H, AcDFR, AcUFGT) and transcription factors (AcMYB10, AcbHLH5) may be involved in the pigmentation of the red-fleshed A. chinensis, whereas AaF3H, AaF3GT, and AaMYB110 may play important roles in the pigmentation of the purple-fleshed A. arguta. This study provides broader insight into the variation in flavonoid profiles among kiwifruit/berry, evaluates the flavonoid nutrition of the four cultivars, and provides additional evidence for the correlation between the genes and metabolites involved in flavonoid synthesis.