EFFECTS OF ACC (1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID) APPLIED THROUGH THE ROOTS OF MAIZE SEEDLINGS ON VEGETATIVE AND EARLY REPRODUCTIVE DEVELOPMENT OF THE SHOOTS

Maize plants, grown in aerated solution cultures, were exposed, at dif ferent growth stages, to ACC (1-aminocyclopropane-1-carboxylic acid) a pplied through the roots for up to 9 d. Total uptake of ACC increased with seedling size. During ACC treatment, ethylene evolution, by the s hoots, proceeded at an almost constant rate per unit fresh weight that was up to 40-foId faster than that of untreated plants. This stimulat ion extended several days beyond the period of ACC uptake. The effects on growth and development were assessed when plants were 50 - 52-d ol d. ACC application shortened certain stem internodes, leaf-sheaths and laminae. The location of these effects depended on the time of applic ation. The greatest shortening was induced by application, at the 4-le af stage (10 d-old), prior to elongation of the cone of the shoot apex . This is ascribed to effects on meristematic tissue, in addition to t hose on elongating cells. An unexpected response to ACC treatment, at the 4-leaf stage, was an increase of up to four leaf-bearing stem node s compared to untreated plants. This resulted in a parallel elevation of the uppermost ear-bearing axillary shoot to higher nodal positions. The length of leaves high in the canopy (nodes 11-16) was promoted by treating seedlings with ACC. The only clear effect of the ACC treatme nts on emergent axillary shoots per se was a retardation of silk elong ation.