A whole-plant analysis of the dynamics of expansion of individual leaves of two sunflower hybrids
Journal of Experimental Botany
Common features in the time-course of expansion of leaves which considerably differed in ®nal area, due to phytomer position, growing conditions and genotype, were identi®ed. Leaf development consisted of two phases of exponential growth, followed by a third phase of continuous decrease of the relative expansion rate. The rate and the duration of the ®rst exponential phase were common to all phytomers, growing conditions and genotypes. Leaves differed in the rate and the duration of the second
... tion of the second exponential phase. The decrease of the relative expansion rate during the third phase depended on neither genotype nor growing conditions. It was phytomerdependent and was deduced from the rate of the second phase via a parameter common to all cases studied. Differences in ®nal leaf area among growing conditions were linked to different expansion rates during the second exponential phase. The duration of the phases at any given phytomer position was the same for the two hybrids in different growing conditions. The dates of developmental events (initiation, end of the two exponential phases, full expansion), and the rate of the second exponential phase, were related to phytomer position, de®ning a strict pattern of leaf development at the whole plant level. Using this framework simpli®ed the analysis of the response of leaf expansion to genotype and environment.