Plant Hormones • Five known classes of hormones control plant growth and development • Auxin – promotes fruit growth • Cytokinins – stimulate cell division • Gibberellins – stimulate growth in leaves and stems • Abscisic Acid – slows plant growth • Ethylene – inhibits root growth
Tropisms • Phototropism –bends shoot towards light; enhances photosynthesis • Gravitropism – uses specialized plastids (statoliths). • Roots display positive gravitropism (grows down towards the earth) and the shoot displays negative gravitropism (grows up out of the earth)
Tropisms • Thigmotropism: • Developmental response to mechanical stimulation • Example: thicker stemmed plants are found in locations where the winds are strong
Turgor Movements • Turgor movements are relatively rapid, reversible plant responses
Biological Clocks • Biological clocks control circadian rhythms in plants and other eukaryotes
Photoperiodism • Photoperiodism synchronizes many plant responses to changes of season
Phytochrome • Phytochrome functions as a photoreceptor in many plant responses to light and photoperiod
Control Systems • Control systems enable plants to cope with environmental stress
Plants • The study of plants began when early humans began to distinguish edible plants from poisonous ones. • Then began to make things from wood and other plant products.
Modern Science • Today scientists aim for increasing crop productivity, but the fun of discovery is what motivates most plant scientists.
Plants • Plant biology, one of the oldest branches of science, is driven by curiosity and need – curiosity about how plants work and a need to feed, clothe, and house an increasing human population. Plant biology is in the midst of a renaissance, in which new methods, coupled with clever choices of experimental organisms, have catalyzed a research explosion.