14.4 Plant Growth. The Role of Plant Hormones. Hormones play a part in regulating a plant's growth. One example is gibberellin (gihb ur EHL ihn). About a hundred years ago, Japanese rice farmers observed that some of their rice seedlings grew abnormally tall.
The Role of Plant Hormones
About a hundred years ago, Japanese rice farmers observed that some of their rice seedlings grew abnormally tall.
Gibberellin can make dwarf plants grow tall, flowers produce seedless fruits, and plants flower prematurely.
Turning in response to an environmental stimulus, such as light or gravity, is called tropism (TROH PIHZ uhm).
Auxin causes the stem cells on the shaded side to grow longer, making the stem bend toward the light.
Plants have a light sensitive chemical that helps them measure the length of periods of darkness and light.
Autumn-blooming plants, such as chrysanthemums, are short-day plants.
The life span of a flowering plant is measured in one-year growing seasons.
Some plants, called annuals, complete their entire life cycle within one growing season.
During the first growing season, the plant germinates and develops roots, stems, and leaves.
During the second growing season, the plant flowers, produces seeds, then dies.
Other plants, called perennials (pur EHN ee uhls), live for many growing seasons.