Ecology: Biology of Interaction. 5.18. Photoperiodism
Photoperiodism is regulation of the seasonal cycle depending on day length, a regulatory mechanism widespread in temperate zones. Unlike circadian rhythms, which are controlled by alternation of light and darkness, annual (circannual) rhythms are controlled by day length.
Ukrainian language (latest version) / Russian language (updates stopped)
5.17. Adaptive Biological Rhythms
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction, Chapter 5. Autecology and Fundamentals of Environmental Science
5.19. Thermobiological Types of Organisms
5.18. Photoperiodism Photoperiodism is the reaction of organisms (animals, plants, fungi) to the relative duration of day and night (photoperiod). Photoperiodism ensures the seasonal synchronization of biological processes. Day length and seasons The duration of daylight depends on latitude and season (Fig. 5.18.1). Unlike temperature and precipitation, it is absolutely predictable. This makes it an ideal signal for predicting upcoming seasonal changes. That is why evolution has developed mechanisms of photoperiodic responses in most groups of living organisms. Types of photoperiodic reactions Photoperiodism determines numerous seasonal phenomena: — in plants — the beginning and end of the growing season, the transition to flowering, the formation of storage organs, leaf fall; — in animals — migrations, hibernation, reproduction, molting. Depending on the duration of illumination required for a particular reaction to occur, the following are distinguished: — short-day plants (SD) — react when the daylight duration decreases below a critical value; — long-day plants (LD) — react when the critical day length is exceeded; — day-neutral plants (DN) — react very little to day length. Animals with long-day reproduction begin to spawn with increasing day length in spring; with short-day reproduction — with its decrease in autumn. Mechanism of photoperiodic response In plants, photoperiodism is associated with phytochrome, a photoreceptor that exists in two interconvertible forms: Pr (active, absorbs red light) and Pfr (inactive, absorbs far-red light). At night, Pr slowly converts to Pfr. If the night break is long enough, the plant registers a "long night" (i.e., a "short day"). Interrupting the night with even a short flash of light cancels this reaction. In animals, the photoperiodic signal is perceived through the visual pathway and regulated by melatonin (a hormone of the pineal gland produced in darkness). The duration of nocturnal melatonin secretion informs the organism about the length of the night. Additional materials: Educational model: Photoperiodism
5.17. Adaptive Biological Rhythms
D. Shabanov, M. Kravchenko. Ecology: Biology of Interaction, Chapter 5. Autecology and Fundamentals of Environmental Science
5.19. Thermobiological Types of Organisms