Q.
Through their effects on plant growth regulators, what do the temperature and light control in the plants?
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AIPMTAIPMT 2012Plant Growth and Development
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Solution:
Light and temperature may affect flowering in plants in various ways. The effect of photoperiods or daily duration of light hours (and dark periods) on flowering is called photoperiodism. For example, in short day plants flowering occurs when day length is below critical period, e.g., dahlia, rice etc. In long day plants, flowering occurs when day length is above critical period, e.g., spinach, lettuce etc. In short-long day plants, short photoperiod is required for floral initiation and long photoperiod is required for blossoming and vice-versa for long-short day plants. Photoperiodic response is mediated by Plant Growth and Development 203 phytochrome, a pigment which perceives the photoperiod stimulus in leaves. It shows reversible change in red and far-red wavelength. Besides correct photoperiod, some plants require low temperature for flowering. These plants remain vegetative during the warm season flower in winters on receiving low temperature. This was found by Lysenko, that the cold requiring annual and biennial plants can be made to flower in one growing season by providing low temperature treatment (vernalization). Stimulus of vernalization is perceived by meristematic cells, e.g., shoot tips, root apex, etc., and is named as vemalin.