Plants are creatures of the sun—they require light as their source of energy. Plants regulate the directions and rates of the growth of their shoots in ways that maximize photosynthesis. To obtain enough light to meet their needs, plants display their leaves to the sun. Some follow the sun with their leaves as the day progresses. Many adjust their growth rates to avoid shading by competing plants. Growth regulation thus affects the interactions of a plant with other plants.
Plants monitor their environment with the help of photoreceptor molecules that sense light signals. Chemical signals called hormones carry information throughout the plant body about light and other aspects of the environment inside and outside the plant. These signals regulate the development of the plant throughout its life history, affecting processes as diverse as stem growth, flowering, bud dormancy, and the dropping of leaves in autumn. Recent advances in understanding plant growth and development have come largely from work with Arabidopsis thaliana, a little mustard-like weed. This plant is useful to researchers because its shoots and seeds are tiny and because it flowers and forms seeds in a relatively short time after growth begins. In addition, its genome is unusually small for that of a flowering plant. Arabidopsis mutants with altered developmental patterns provide evidence for the mechanisms of hormone and photoreceptor action.
Catching Some Rays Most of us have observed the manner in which plants turn their flowers or leaves toward sunlight. Light signals caught by photoreceptor pigments are transmitted by hormones to other parts of the plant in a finely tuned developmental dance.
In this chapter we will give a brief overview of the life of a flowering plant and its developmental stages. We will explore the environmental cues, photoreceptors, and hormones that regulate plant development and consider their multiple roles.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.