The distribution of elongation and surface pH patterns along the primary roots of maize (cv. LG 11), maintained vertically in humid air (darkness, 22°C), have been analysed quantitatively. A new technique employing Sephadex G 25 beads containing a pH indicator dye (bromocresol purple), was used for measuring both the growth gradient of the roots (Sephadex beads as markers) and at the same time, the surface pH changes (referring to a standard scale). The optimal axial growth was located between 2 and 4 mm from the tip. This coincides with the optimal decrease in surface pH.

Roots of Zea mays were maintained in a vertical orhorizontal position and the local elongation rate and H(+) fluxes were measured using Sephadex beads containing a pH indicator. When the roots were kept horizontally, the growth of the lower side was strongly inhibited and that of the upper side slightly stimulated as compared with vertical roots. The H(+) extrusion, which was greatest in the elongation zone, was strongly inhibited on the lower side and slightly stimulated on the upper side as compared with vertical roots.

The elongation rate, the gradient of the local elongation rate and the surface pH of maize roots were measured over 12 h. A data bank was constituted by storing these values. By sorting these results on the basis of different elongation rates, different classes of root were obtained. Two classes were chosen: the low-growth roots and the high-growth roots. The mean growth of these two root classes was stable with time and differed significantly from one another. The surface pH of the elongation zone was the same for the roots of these two classes, but the roots selected for their higher growth rate had a larger acid efflux in this zone.

No abstract