Photoperiodism

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Photoperiodism

Photoperiodism (/ˌfoʊtoʊˈpɪriədɪzəm/) is a biological response of organisms to the length of day or night. It is a phenomenon in which the physiological reactions of an organism, especially the initiation of flowering and reproduction in plants and the regulation of reproduction and coat growth in animals, are controlled by the length of daylight and darkness in a 24-hour period.

Etymology

The term "Photoperiodism" is derived from three Greek words: "photo" meaning light, "period" meaning a cycle or length of time, and "ism" denoting a practice or system. It was first described in 1920 by the American scientists Garner and Allard.

Types of Photoperiodism

Photoperiodism can be classified into three types:

  • Short-day plants (SDPs): These plants flower when the night length exceeds a certain duration. They require a long period of darkness and short day length to induce flowering.
  • Long-day plants (LDPs): These plants flower when the day length is longer than a certain duration. They require a short period of darkness and long day length to induce flowering.
  • Day-neutral plants (DNPs): These plants flower regardless of the length of day or night. They are not influenced by the photoperiod.

Mechanism of Photoperiodism

The mechanism of photoperiodism involves the perception of light by a pigment called phytochrome. This pigment absorbs red and far-red light and undergoes a transformation between two forms: the red light-absorbing form (Pr) and the far-red light-absorbing form (Pfr). The ratio of these two forms in the plant cells influences the plant's response to photoperiod.

Related Terms

  • Circadian rhythm: The physical, mental, and behavioral changes in an organism that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism's environment.
  • Chronobiology: The field of biology that examines periodic (cyclic) phenomena in living organisms and their adaptation to solar- and lunar-related rhythms.

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