XVI International Botanical Congess

The use of the plastochron index (PI) as a numerical measure of leaf developmental age was introduced for A. thaliana. A standardized statistical methodology was formulated to validate the PI for leaf development. The PI was the ideal choice for determining leaf age because it lowered the temporal variation relative to using plant age in days. Tooth development was compared between the Columbia-1 (Col-1) ecotype and se, a mutant with deeper teeth. The se mutant initiated teeth earlier in leaf development than did Col-1. Besides leaves, the PI can serve as the time variable for other modules such as: flowers, inflorescences, internodes, and stem units. The PI has found utility in physiology, anatomy and growth modeling, but it ought to be used more in quantitative studies of molecular genetics, plant development and testing hypotheses of heterochrony in plants.