Vessel differentiation in the pedicel of apple and the effects of auxin transport inhibition.

The growth dynamics of vessel formation and the effect of auxin transport inhibition on vessel differentiation were investigated in the pedicel of developing apple (Malus domestica Borkh.). Quantitative microscopic analysis showed that a majority of vessels were differentiated pre-bloom with the commencement of pedicel extension but that the full conducting capacity of the xylem was attained shortly after bloom. The effect of a post-bloom application of N-(1-Napthyl)phthalamic acid showed that an auxin-like signal emanating from the young fruit not only stimulated vessel differentiation in the pedicel but also controlled fruit abscission and the development of the seed and fruit.