Développement du fruit de Prunus virginiana (Rosaceae)

Abstract

The development of the fruit of Prunus virginiana L. is followed from full bloom to ripening. The maturation process, which lasts 10 weeks is characterized by three distinct stages. Two periods of rapid growth (at the beginning and the end of ripening) are separated by a stage of retarded growth. Soon after the fertilization, the mesocarp increases in thickness, owing to an enlargement of the cells of the later tissue rather than by an increase in the number of cells. By the end of the first period of growth, the endocarp begins to enlarge. In this situation, the increase of thickness is predominantly due to cell division. At the completion of its development, we observed two distinct zones in the endocarp. The inner portion is formed of 6 to 7 layers of lignified cells extending tangentially along the cavity, while the outer portion is composed of 15 to 20 isodiametric sclereids. The second stage of the development is characterized by an important delay in the growth of the pericarp. However, the cessation of the increase coincides with some important changes in the seed, while the endosperm, and almost simultaneously, the embryo rapidly expand. During the maturation of the seed, we noted that the endosperm cells enlarged, their cytoplasm became thicker, and their arrangement in the tissue appeared more regular. Throughout the third phase of the development, a new period of rapid growth is observed. In the mesocarp, the cells enlarged in the radial direction. The development of the fruit of P. virginiana L. and its vascular patterns have been analysed in comparison with those of other fruits of Prunus.