Presentation on theme: "Plant Responses to Signals Chapter 39. Plants have to respond to gravity and other stimuli in environment. Growth pattern in plants - reaction to light."— Presentation transcript:
Hormones Plants produce hormones that regulate growth and development. Hormones - chemical signals produced in one part of body, transported to other parts. Growth towards or away from stimuli (regulated by hormones) - tropism.
Gibberellins stimulate growth in leaves and stems - little effect on root growth. Stems, gibberellins stimulate cell elongation and cell division. Gibberellins applied to dwarf plants - grow to normal height. Applied to normal plants - nothing happens.
Abscisic acid promotes plant to become dormant; thought to help leaves drop in fall. Sometimes seed will need to have all abscisic acid removed (through washing) to break dormancy. Also helps to withstand drought - sends plant into dormancy until the conditions are favorable again.
Ethylene promotes leaf dropping as well as fruit ripening. If fruit producing ethylene placed with fruits that are not, those fruits will also ripen in response to hormone. By losing leaves during fall, plants prevent drying out during winter.
Responses to light Plants require light to grow; can absorb various aspects of spectrum of light. Respond differently to different wavelengths of light. 2 different types of plants, short day and long day.
Short-day plants - long-night plants -require minimum length of uninterrupted darkness. Long-day plans - short-night plants - require period of continuous darkness interrupted by few minutes of light. Response to light - photoperiodism.
Tropisms Roots - positive gravitropism (grow in direction of gravity); shoots - negative gravitropism (grow against direction of gravity). Thigmotropism - response to touch; in some plants, causes plant to coil around an object (like tendril).
Some plants cannot grow in extreme temperatures or salinities; others thrive in them. Freezing of cytoplasm can kill plant because excess ions can accumulate.
http://www.learnnc.org/lp/media/collections/cede/resized/cedebwr07.jpg Marsh grasses are often tolerate of extreme salinities
Plant defenses Plants susceptible to many different bacteria and viral infections because of place in food chain. Eaten by herbivores - need protection against excess herbivory – use physical defenses, such as thorns, and chemical defenses, such as production of toxic compounds.