Dynamics of the Elongation of Internodes in Maize ( Zea mays L.): Analysis of Phases of Elongation and their Relationships to Phytomer Development

Abstract The kinetics of elongation of individual internodes of maize stems were studied under field conditions. Thermal time courses of internode length were recorded using non-destructive methods, based on direct measurement of X-ray photographs or on indirect estimates using heights of leaf collars. These data were complemented by serial dissections of maize stems, and by precise observation of the process of sheath emergence, to specify its role in the kinetics of internode elongation. The kinetics of elongation were found to be composed of four phases. The rate of elongation rises exponentially during phase I, and then increases sharply during a short period (phase II), which is followed by a major period of constant growth rate (phase III) and a shorter period in which the rate declines (phase IV). During phase I, elongation appears to be integrated at the level of the whole apical cone. From phase II onwards, elongation becomes determined at the level of the phytomer. The emergence of the sheath attached to the internode appears to be a possible trigger for the transition between phase I and phase II, and it may also be involved in variation in final length among phytomers.