Asian Online Journals (www.ajouronline.com) 296 Tassel Initiation is Synchronized to the Elongation Rates of Leaf

ABSTRACT — Plants must coordinate the environmental conditions with internal cues in order to transition from vegetative to floral development at a time when reproductive success is likely. In this study, the association between primordial leaf growth and floral initiation in controlling that transition was examined. Maize plants grown under different photoperiod, light intensity and defoliation treatments were dissected at frequent intervals to measure the growth of exposed and unexposed leaves and determine the developmental stage of apical meristem. A gradual decrease in relative elongation rates of successive leaf primordia and unexposed young leaves was observed as plants increased in size from seedling emergence until tassel initiation. Earlier-formed leaf primordia elongated at a higher relative rate than did younger, latter-formed leaf primordia. More importantly, this gradual decrease in early stage leaf growth and the resultant accumulation of unexposed leaves in the whorl were found to be associated with floral transition. Immediately prior to tassel initiation, the length of corresponding leaf primordia in plants of the same or different treatments was similar. Treatments including photoperiod extension and defoliation that delayed tassel initiation, and shading that reduced growth were also marked by a syncronized modification of leaf primordia elongation. Floral transition occurred when the slow-down in leaf primordia elongation and the resultant accumulation of leaf primordia reached a certain level. The elongation rate of leaf primordia could regulate floral transition in maize