94221420 Howe Daylength, or photoperiod, is one of the most important environmental cues controlling the onset of dormancy in perennial plants. Short days induce growth-cessation, the initiation of cold-acclimation, and the formation of a terminal bud. By responding to daylength, the initiation of dormancy can be closely synchronized with the end of the growing season and plants can begin acclimating prior to the onset of low temperatures in the fall. Because the length of the growing season varies latitudinally, photoperiodic ecotypes have evolved in species with large latitudinal distributions. In the northern hemisphere, for example, trees from nothrern locations respond to longer photoperiods and initiate dormancy earlier in the season than do southern genotypes. Differences in response occur even when the ecotypes are grown in common-garden tests under the same photoperiodic regime, demonstrating that photoperiodism is under strong genetic control. The long-term goals of this project are to determine the genetic basis of photoperiodic ecotypes in perennial plants and to characterize the early events in short-day induced bud set, using black cottonwood as a model species. This research will integrate information on photoperiodism at the populational, whole-plant , and molecular genetic levels in order to understand the evolutionary processes leading to ecotypic variation in plants. Because both the timing of bud set and plant architecture are important determinants of plant productivity, this research has important implications for plant breeding. This research will also add to our understanding of the ecological role of phytochrome in plants.
