Lecture 7B Notes Plant Science 3500 Lecture 7B - Hormonal Regulation of Growth Plants respond to stimuli in their environment such as temperature , light , gravity , and mechanical disturbance . As we have already seen, many of these responses are controlled by way of plant growth regulators. The responses of plants to their environment allow them to survive seasonal change through effects on growth, reproduction and dormancy. Seasonal changes in the environment of a plant can have a profound effect on development. Probably the most important response for the long-term survival of plants, especially annuals, is flowering.
Some plants flower early in the growing season, while some flower later in the year.
Photoperiodism Garner and Allard noticed that while most of the tobacco plants they were working with flowered in August, a mutant cultivar called Maryland Mammoth didn t flower in the field during the summer, or even in the greenhouse until December. The plant was tall with large leaves, which were desirable characteristics, but to use it in a breeding program, it needed to flower in the field during the same time period as the other tobacco plants. Something other than the age or maturity of the plant was determining flowering date. Garner and Allard tested the effect of different levels of moisture, temperature, nutrition, and light on the flowering of these plants, but it was only when they thought to vary the length of the daylight period that they found the environmental cue that influenced flowering. In further experiments, they found that while some plants, like tobacco and soybeans, flowered in response to daylengths that were shorter than some maximum , other plants, including many of the grasses and cereal grains, flowered in response to daylengths that were longer than some minimum .