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Phototropism

Phototropism In Nature

Laboratory studies of phototropism have a bearing upon the life of plants in nature. It is advantageous for a young seedling, such as a coleoptile, to bend toward the light so that its leaves can intercept more sunlight for photosynthesis and grow faster. Phototropism is also related to solar tracking, the orientation of a plant's leaves in response to the Sun. Unlike the response in coleoptiles, which is caused by differential stem growth, solar tracking responses in most species are caused by pressure changes in special cells at the leaf base. Depending on the species and other factors, the blades of a mature leaf may be oriented perpendicular to the Sun's rays to maximize photosynthesis or parallel to the Sun's rays to avoid over-heating and desiccation.

Resources

Books

Hart, J.W. Plant Tropisms and Other Growth Movements. London: Routledge, Chapman & Hall, 1990.

Peter A. Ensminger

KEY TERMS

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Agar: —Carbohydrate derived from a red alga which biologists use in a gel form for culture media or other purposes.
Bioassay: —Estimation of the amount of a substance, such as a hormone, based upon its effect on some easily measured response of an organism.
Coleoptile: —Hollow sheath of tissue which surrounds the stem of young grass plants.
Gravitropism: —Orientation of an organism in response to gravity.
Nastic movement: —Growth movement controlled by external or endogenous factors in which the orientation of the movement is not determined by an external stimulus.
Tropism: —Orientation of an organism in response to an external stimulus such as light, gravity, wind, or other stimuli, in which the stimulus determines the orientation of the movement.

Additional topics

Science EncyclopediaScience & Philosophy: Philosophy of Mind - Early Ideas to Planck lengthPhototropism - History Of Phototropism Research, Cholodny-went Theory, The Photoreceptor Pigment, Phototropism In Other Organisms