How plants move and communicate Plant Responses How plants move and communicate

The houseplant observation For years, people noticed that houseplants tended to lean toward a source of light. Charles Darwin and his son Francis, wondered why. How does a plant “know” where to lean?

Tropisms Tropisms are the growth of a plant toward (positive) or away (negative) from a stimulus.

Phototropism Tendency for a plant to grow towards light. Look at the sprouts in the bottom picture and the explanatory diagram at the top. Explain why the sprouts are all leaning in the same direction.

Gravitropism In this Impatiens plant, shoots grow upwards and roots grow downwards in response to gravity.

Hydrotropism Hydrotropism is a plants growth response to water concentrations. The response can be positive (towards the water) or negative (away from the water). Roots, for instance, are positively hydrotropic. That means that they grow towards moist soils to avoid draught stress. Once a root cap has sensed water it bends and then the root grows towards it.

Thigmotropism In some plants, vining stems or tendrils will grow in response to touch.

Nastic Movements

Nastic movement in the sensitive plant (Mimosa pudica)

Hinge control in Venus Fly Trap - Nastic movement

How it works Nastic movements are rapid, reversible movements in a plant. Electrical potentials across cell membranes, similar to those in our nerve cells, signal plant cells at the base of the Mimosa leaf to rapidly lose water. This causes the leaf to droop.

Other examples Sunflowers follow the sun during the day. Leaves of many plants turn to follow the sun.

Day/Night length Some plants flower in response to the length of periods of darkness. Spring-blooming flowers are long night (short day) plants, while summer- blooming flowers are short night (long day) plants. Some plants are day-neutral.

Movies Sensitive Plant: http://www.youtube.com/watch?v=BVU1YuDjw d8 Venus Fly Trap: http://www.youtube.com/watch?v=ktIGVtKdgw o&feature=related