During maturation of some apple cultivars, changes in anthocyanin synthesis were examined in fruits being exposed to white light (9.3Wm^-2) or white plus ultraviolet light with an emission peak at 312nm (white+UV312, 5.3Wm^-2 in total).
Varying levels of anthocyanin synthesis under white+UV312 light appear to represent changes in the ability of the fruit to accumulate anthocyanin, since white+UV312 light was very influential in anthocyanin synthesis. Under white+UV312 light, bagged fruit which had been covered with paper bags since about one month after flowering produced much higher anthocyanin at immature and mature stages than non-bagged ones, regardless of cultivar. This anthocyanin synthesis, however, remarkably decreased during ripening, as measured by increased ethylene concentration in the cortical tissue. In non-bagged fruit of most red cultivars, increase in anthocyanin synthesis occurred before the fruit began to ripen. Anthocyanin synthesis in ‘Starking Delicious’ (‘SD’), ‘Jonathan’ and ‘McIntosh’ continued increasing during ripening, while that in ‘Tsugaru’, ‘Jonagold’ and ‘Rails Janet’ peaked concurrently with initial stage of ripening, then decreased sharply.
‘SD’ and ‘Jonathan’ produced higher anthocyanin levels under white light as well as under white+UV312 light. In cultivars such as ‘Tsugaru’ and ‘Fuji’, anthocyanin synthesis was less than in ‘SD’ and ‘Jonathan’, especially under white light. ‘Mutsu’ and ‘Golden Delicious’, yellow-colored cultivars, produced small amounts of anthocyanin only under white+UV312 light. Thus the responsiveness to light, especially to white light, differed considerably with cultivars. In cultivars such as ‘Tugaru’ and ‘Mutsu’, the light of UV region is probably indispensable for developing red color. This spectral sensitivity characteristic of anthocyanin synthesis was not altered by bagging treatment. The beginning of increase in anthocyanin synthesis under white light coincided with increasing ethylene concentration; this suggested that ripening led to increase in the responsiveness to white light.