|MadSci Network: Botany|
Why questions are often difficult to answer. Plants respond differently to various colors, or wavelengths, of light because they have evolved pigments that preferentially absorb one color more than others. For example, phototropin is a pigment that preferentially absorbs blue light. Phototropin causes phototropism, a bending response toward a light source. Therefore, phototropism only occurs if the light source contains blue wavelengths. Being able to sense different colors of light with pigments allows plants to respond to their environment in several ways. For example, being able to differentiate between red and far-red light with the pigment phytochrome allows plants to sense the daylength, or photoperiod, and thus, the time of year. Phytochrome is important in timing of flower production and determining when deciduous trees lose their leaves and go dormant in the fall. For more details, try searching for photomorphogenesis, which is defined as light regulation of plant growth and development. References Phototropism - Do Fast Plants Prefer the Blues Photomorphogenesis, Phytochrome Use of Light Quality to Regulate Horticultural Crop Morphogenesis
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