Physical Constraint and Tiller Growth in Wheat

Abstract

Young wheat seedlings were subjected to mild physical constraint by placing short plastic collars with internal diameters of 1.5, 1.7 and 2.0 mm around the coleoptile close to the grain. In others the natural constraint of the coleoptile was reduced experimentally by making a vertical slit just above the site of the coleoptile tiller. The narrowest of the plastic collars reduced the growth of the primary shoot, but the others did not. Collars of all sizes prevented the emergence of all tillers sited immediately within them, though the coleoptile tiller, and occasionally the first tiller 'escaped' through the coleoptile or leaf sheath tissues below the collar. The coleoptile tillers of about half of the surgically treated seedlings grew vigorously, but those of the control plants did not. The results are interpreted as supporting the hypothesis that physical constraint can be an impor- tant determinant of developmental events within shoot apical systems.