Temperature and light are important environmental factors that affect flavonoid biosynthesis in grape berry skin. However, the interrelationships between temperature and light effects on flavonoid biosynthesis have not been fully elucidated at the molecular level. Here, we investigated the effects of temperature and light conditions on the biosynthesis of flavonoids (anthocyanins and flavonols) and the expression levels of related genes in an in vitro environmental experiment using detached grape berries. Sufficient anthocyanin accumulation in the grape skin was observed under a low temperature (15 °C) plus light treatment, whereas high temperature (35 °C) or dark treatment severely suppressed anthocyanin accumulation. This indicates that the accumulation of anthocyanins is dependent on both low temperature and light. qRT-PCR analysis showed that the responses of three MYB-related genes (VlMYBA1-3, VlMYBA1-2, and VlMYBA2) to temperature and light differed greatly even though the products of all three genes had the ability to regulate anthocyanin biosynthesis pathway genes. Furthermore, the expression levels of other MYB-related genes and many flavonoid biosynthesis pathway genes were regulated independently by temperature and light. We also found that temperature and light conditions affected the anthocyanin composition in the skin through the regulation of flavonoid biosynthesis pathway genes. Our results suggest that low temperature and light have a synergistic effect on the expression of genes in the flavonoid biosynthesis pathway. These findings provide new information about the relationships between environmental factors and flavonoid accumulation in grape berry skin.

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As a result of natural hybridization and human selection over millennia, the skin colors of grapes have become greatly diversified. The color is determined by the quantity and composition of anthocyanins. Color-skinned cultivars accumulate anthocyanins in their skins, whereas white-skinned cultivars do not. Myb-related transcription-factor genes such as VvmybA1 regulate anthocyanin biosynthesis. VvMYBA2r, VlmybA1-1, VlmybA1-2, and VlmybA2, which are homologs of VvmybA1, also regulate anthocyanin biosynthesis. In this study, we isolated a novel Myb-related sequence, VlmybA1-3, from cultivars of Vitis labruscana (Vitis vinifera x Vitis labrusca) by means of inverse PCR, and confirmed by means of transient gene expression assay that the gene regulates anthocyanin biosynthesis in grape berry skin. Seedlings of V. labruscana with two functional haplotypes at a region of berry color loci accumulated more anthocyanins than seedlings with a single functional haplotype. In addition, we investigated the haplotypes at the region in 35 cultivars (both V. vinifera and V. labruscana), and found certain typical characteristics. These findings will contribute to the selection of seedlings with high anthocyanin quantities in breeding programs for wine and table grapes, and will help elucidate the origin and evolution of Vitis species.

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Mechanisms of sugar accumulation in response to drought stress in Satsuma mandarin (Citrus unshiu Marc.) fruit were investigated. Predawn leaf water potentials averaged -0.35MPa for well-watered, -0.60 MPa for moderately drought-stressed, and -1.00 MPa for severely drought-stressed glasshouse-grown 3-year-old trees. Fruit peel turgor and fruit growth of the moderately drought-stressed trees recovered to a similar value to that of the well-watered trees. Photosynthetic rates and stomatal conductance of both moderately and severely drought-stressed trees were significantly lower than those of the well-watered plants. However, the total sugar content per fruit of moderately drought-stressed trees was the highest among the drought treatments. A 13C-labeling experiment showed that 13C distribution in fruit grown under the moderately drought-stressed condition was the highest. These findings indicate that sugar accumulation in fruit was caused by an increase in translocation of photosynthates into fruit, especially into the juice sacs, under drought stress.