The hunt for the purple strawberry: change in anthocyanin profile leads to a colour change from red to burgundy
Strawberries are traditionally perceived as red fruit, owing to the predominance of the red anthocyanin pigment, pelargonidin. Some fruit breeding lines however, are very dark in colour, displaying an almost burgundy, or purple, pigmentation. This difference in colour is more reminiscent of the anthocyanin cyanidin, rather than pelargonidin, leading to the possibility that a different predominating anthocyanin to pelargonidin may exist in the 'purple' fruit. Strawberry fruit exhibiting red or burgundy skin colour, red or burgundy flesh colour, or a combination of both, were assessed for their anthocyanin profiles in skin and flesh tissues. Achenes were removed from the fruit surface and analysed separately. Anthocyanin was also analysed in other plant tissues, including leaves, petioles, and coloured petals. Pelargonidin-3-glucoside was identified as the predominant anthocyanin in both skin and flesh of red and burgundy-coloured fruit tissue. Cyanidin-3-glucoside was also present, but at a significantly higher percentage in burgundy tissue (12-19%) compared to red tissue (1-7%). In addition, burgundy-coloured tissues had significantly higher total anthocyanin concentration than red-coloured tissues. Interestingly, only cyanidin-3-glucoside was present in leaf lamina, petioles, and coloured petals, and was also the predominant anthocyanin in achenes from the fruit surface. The predominance of pelargonidin only in the fruit flesh of strawberries, may indicate that the ability to convert the pelargonidin precursor, dihydrokaempherol, to the cyanidin precursor, dihydroquercetin, is more actively downregulated in strawberry fruit tissue. The reason for this may have been to increase the visibility of the forest progenitors of strawberry fruit to seed-dispersing herbivores. The current purple-fruited breeding lines would appear to exhibit a partial reversal of this downregulation, and a manyfold increase in total anthocyanin concentration, leading to a deeper overall fruit colour.
O¿Hare, T.J. and Hong, H.T. (2021). The hunt for the purple strawberry: change in anthocyanin profile leads to a colour change from red to burgundy. Acta Hortic. 1309, 1047-1052
purple strawberry, cyanidin, pelargonidin, pigmentation, achene, leaf, flavonoid-3-hydroxylase