Hideo Bessho

UDP-sugar biosynthetic pathway: contribution to cyanidin 3-galactoside biosynthesis in apple skin

UDP-galactose:flavonoid 3-O-galactosyltransferase (UFGalT) is responsible for cyanidin 3-galactoside (cy3-gal) synthesis from cyanidin (cy) and UDP-galactose (UDP-gal) which are, respectively, catalyzed by anthocyanidin synthase (ANS) and UDP-glucose 4-epimerase (UGE). To clarify the contribution of UDP-galactose pathway to cy3-gal accumulation in apple skin, we analyzed the contents of UDP-gal and UDP-glucose (UDP-glu), cy, and, cy3-gal contents along with UGE activity. We confirmed that transcript levels for apple ANS and UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT) coincided with anthocyanin accumulation in three apple cultivars differing in their skin colors. During fruit development, changes in level of cy coincided with that of cy3-gal, whereas UDP-gal and UGE activity showed no similar trend with cy3-gal. Significant correlation was not observed between the changes in UGE activity and UDP-sugar contents. The effect of temperature and UV-B radiation (different environmental conditions) on the accumulation of UDP-sugars, cy and cy3-gal, and UGE activity were also investigated in a pale-red cultivar. High temperature tended to depress the accumulation of both UDP-sugars and cy concomitant with the decrease in cy3-gal content irrespective of UV-B radiation. Although there was no high inhibition of both cy and UDP-sugars at low-temperature without UV-B, cy3-gal accumulation was highly depressed. UGE activity was highest at low temperature with UV-B, but not much different under other conditions. Most of the parameters under different environmental conditions were significantly correlated with each other. Based on these results, contribution of UDP-sugar biosynthetic pathway to anthocyanin biosynthesis under different environmental conditions as well as during fruit development is discussed.

Determination and confirmation of S-RNase genotypes of apple pollinators and cultivars

Summary We analysed the S-RNase genotypes of 23 crab apple (Malus spp.) pollinators and 102 cultivars of domestic apple (Malus pumila Mill.) by PCR amplification and digestion. Within the 23 pollinators, four pollinators, ‘Hopa’, ‘Jack’, ‘Pink Perfection’ and ‘Profusion B’, each had two unidentified S-RNase alleles. These cultivars should be useful pollinators for all domestic cultivars. Twenty-one of the domestic cultivars exhibited S-genotypes contrary to those expected from their supposed parentage, suggesting that one or both reported parents were wrong. We confirmed many of the S-RNase genotypes by pollination tests.