photoperiodism


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Related to photoperiodism: vernalization

photoperiodism

 [fo″to-pēr´e-o-dizm]
the physiologic and behavioral reactions brought about in organisms by changes in the duration of daylight and darkness.

pho·to·per·i·od·ism

(fō-tō-pēr'ē-ō-dizm),
The periodic (seasonal or diurnal) activities, behavior, or changes in plants or animals brought about by the action of light.

photoperiodism

(fō′tō-pîr′ē-ə-dĭz′əm)
n.
An organism's response or ability to respond to changes in photoperiod.

photoperiodism

the response observed in an organism to the relative length of light and dark periods. While all organisms can be affected by PHOTOPERIODS (See also BIOLOGICAL CLOCK the term is most commonly used in connection with higher plants, particularly their flowering. The regulation of flowering is rather complex and difficult to generalize about, but it is possible to divide plants into three categories: LONG-DAY PLANTS, SHORT-DAY PLANTS and DAY-NEUTRAL PLANTS (the latter being unaffected by photoperiod).

Plants appear to detect the photoperiod with the pigment PHYTOCHROME which can exist in two forms in the leaves, P660 in red light and P725 in far-red light. If there is more P660 than P725 in a short-day plant, or P725 than P660 in a long-day plant, then flowering is induced as a vegetative apical MERISTEM is changed to a flowering one.

Phytochromes are also present in the seed coat, the correct balance of P660 and P725 stimulating enzyme activation and hence GERMINATION. See also FLORIGEN.

References in periodicals archive ?
Lewis, "Photoperiodism and seasonal cycles of development," Insect Clocks, pp.
Hardeland, "Photoperiodism and effects of indoleamines in a unicellular alga, Gonyaulax polyedra," Science, vol.
Statistical research has documented seasonal patterns described in terms of sociological and biological factors such as the variations of the circadian biological clock and photoperiodism, variety in terms of neurotransmitters, a.s.o.
Cannabis sativa is an annual plant, growing vegetatively in the early part of its life cycle, and induced to flower by photoperiod, the timing of induction being one of many adaptive features of the plant, discussed in this review (in the "Evolution of Photoperiodism Under Domestication" section).
Specific topics covered include insect-insect and insect-plant interactions, insect biotechnology for pest control, insect photoperiodism and many more.
Study of photoperiodism on gonadal weight in a Readhead bunting under natural day length [Ndl].
Extraretinal photoreception in entrainment and photoperiodism in invertebrates.
Note, however, that flowering, bulb development and pre-dormancy preparation are controlled by length of day (photoperiodism).
Among the topics are lessons on circadian clocks from fish, an update of the morning and evening oscillator model in Drosophila, dynamic neuronal network organization of the circadian clock and possible deterioration in disease, circadian modulation of sleep in rodents, local aspects of sleep revealed by observations from intra-cerebral recordings in humans, feedback actions of locomotor activity to the circadian clock, managing neurobehavior capability when social expediency trumps biological imperatives, the evolutionary physiology of photoperiodism in vertebrates, and circannual rhythm in the varied carpet beetle Anthrenus verbasci.
They are growing their winter fur based on photoperiodism, not temperature.