Ultrastructural study of the effect of abscisic acid on cell elongation in plant cells

An ultrastructural study is presented of the effect of abscisic acid (ABA) on the elongation of cells in the cortical area of Allium cepa roots between 3 and 4 mm from the tip (the area of differentiation). If we take the size ultimately attained by these cells as our point of reference, the elongation is inhibited to the extent of about 2.6 times. The dictyosomes appear to be as numerous and as active in treated as in untreated cells. There is a demonstrably marked increase in the thickness of the longitudinal cell wall due to the equal supply of Golgi vesicles to cover a smaller surface, and the postulate is advanced that ABA mainly affects the absorption of water and diminishes intracellular swelling, to which cell elongation is linked