Scanning Electron Microscopy of Development of Axillary Buds in ‘Nankoh’ Japanese Apricot

Abstract

Axillary buds were collected at 2-week intervals from middle portion of short, intermediate, long and water shoots of ‘Nankoh’ Japanese apricot trees grown in the field. Inner morphological change of these buds was examined with using scanning electron microscopy. The structure of axils subtended by folded and just unfolded leaves at upper portion of young shoot was also examined.
In the axils at the upper portion of the shoot, a larger tissue was formed in the center and two smaller tissues existed facing each other with the central tissue between. The central tissue had a meristem with broad lobed bracts and the lateral tissues had a meristem with slender bracts, the former and the latter developed as a primary bud and accessory buds, respectively. In the accessory buds, the meristem, which did not show any morphological change until early August, flattened in late August and sepals formed around the flattened meristem in September. The size of the accessory bud became larger than that of the primary bud at this time. Formation of floral organs continued without rest until December when ovule was formed. However, little morphological change occurred in the primary bud until early December. These results indicate that the compound bud is formed early time in the axil, flower differentiation started in the accessory bud from mid-August, and the developmental pattern was very different between primary and accessory bud in ‘Nankoh’ Japanese apricot.