Tropism – The Oriented Movement of Plants

What is tropism?

Plants use direct environmental stimuli for orientation in growth and movement. This is called tropism. The responses of the plant may be toward (positive) or away (negative) from the external stimulus or stimuli.

Plants are able to respond to numerous different kinds of external environmental stimuli such as chemicals in the soil, light, water, gravity and more. The growth movements are named according to the stimulus (e.g. stimulus: gravity --> gravitropism).

Click the links below to learn more about the different types of stimuli and the plants reaction to it:

  • Phototropism - Reaction to light and different wavelengths

  • Heliotropism – Reaction to sunlight intensity and direction
  • Photoperiodism - Reaction to the length of light and dark periods
  • Gravitropism (Geotropism) – Reaction to gravity
  • Hydrotropism – Reaction to moisture gradient (water)
  • Thigmotropism – Reaction to touch
  • Thermotropism – Reaction to temperature
  • Chemotropism – Reaction to chemicals

    Despite the above information, plants are generally thought to be immobile. But this is simply not true! Yet, most movements (tropisms) are so slow that our eyes can’t catch them. Speeding up time in time lapse videos show nicely to how extent plants are able to move. This is just amazing and awesome to watch! Actually, producing time-lapse videos of plant movement will be one of my future projects. I just love it!

    However, some plant movements are very quick (nastic movements) and can be observed instantly (opposed to the slower tropic movements). One famous example of a rapid plant movement is the instant reaction of the “touch-me-not”, Mimosa pudica. The leaves fold quickly inward when touched. This is called thigmonasty.

    Another well-known example of a rapid plant movement is the closing of leaves in venus fly traps. These carnivorous plants catch small insects in the blink of an eye.

    But anyway, I got carried away now from the topic of tropism. But plant movement, slow or fast, is a fascinating topic! And, just quickly, what is the big difference between slow and fast movements? Directional stimuli provoke slow (tropic) movements and non-directional stimuli provoke fast (nastic) movements.

    What Causes this Plant Growth Process?

    Ok, we have seen that plants are quite able to move around. But how do they do it? How do they recognize a stimulus and how are they able to react to it?

    Well, it has all to do with stimulus receptors and with plant hormones. The perception of plants (plant physiology) is the ability to sense environmental stimuli and to adequately and most beneficially react to them.

    Plant stimuli receptors act on a cellular level and their nature depends upon the kind of stimulus. They received signals are then amplified and transformed (with the help and interaction of hormones) into a physiological response.

    Auxins are plant hormones that regulate the growth of a plant. These hormones are also believed the most important ones to control the movements towards to or away from an external stimulus, thus tropism.

    Tropism and the involved Plant physiology is a wide topic for me it comes to this: Plants are indeed very complex and not at all fully understood living organisms!

    Return from Tropism to the Plant and Flower Guide

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