|
Photoperiodism is the physiological reaction of organisms to the length of day or night. It occurs in plants and animals. Photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light and dark periods. == Plants == Many flowering plants (angiosperms) use a photoreceptor protein, such as phytochrome or cryptochrome, to sense seasonal changes in night length, or photoperiod, which they take as signals to flower. In a further subdivision, ''obligate'' photoperiodic plants absolutely require a long or short enough night before flowering, whereas ''facultative'' photoperiodic plants are more likely to flower under the appropriate light conditions, but will eventually flower regardless of night length. In 1920, W. W. Garner and H. A. Allard published their discoveries on photoperiodism and felt it was the length of daylight that was critical,〔 but it was later discovered that the length of the night was the controlling factor. Photoperiodic flowering plants are classified as ''long-day plants'' or ''short-day plants'' even though night is the critical factor because of the initial misunderstanding about daylight being the controlling factor. Each plant has a different length critical photoperiod, or critical night length.〔 Modern biologists believe that it is the coincidence of the active forms of phytochrome or cryptochrome, created by light during the daytime, with the rhythms of the circadian clock that allows plants to measure the length of the night. Other than flowering, photoperiodism in plants includes the growth of stems or roots during certain seasons and the loss of leaves. Artificial lighting can be used to induce extra-long days.〔 === Long-day plants === Long-day plants flower when the night length falls below their critical photoperiod. These plants typically flower in the northern hemisphere during late spring or early summer as days are getting longer. In the northern hemisphere, the longest day of the year (summer solstice) is on or about 21 June. After that date, days grow shorter (i.e. nights grow longer) until 21 December (the winter solstice). This situation is reversed in the southern hemisphere (i.e., longest day is 21 December and shortest day is 21 June).〔〔 Some long-day obligate plants are: * Carnation (''Dianthus'') * Henbane (''Hyoscyamus'') * Oat (''Avena'') Some long-day facultative plants are: * Pea (''Pisum sativum'') * Barley (''Hordeum vulgare'') * Lettuce (''Lactuca sativa'') * Wheat (''Triticum aestivum'') 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Photoperiodism is the physiological reaction of organisms to the length of day or night. It occurs in plants and animals. Photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light and dark periods.== Plants ==Photoperiodic plant redirects here -->Many flowering plants (angiosperms) use a photoreceptor protein, such as phytochrome or cryptochrome, to sense seasonal changes in night length, or photoperiod, which they take as signals to flower. In a further subdivision, ''obligate'' photoperiodic plants absolutely require a long or short enough night before flowering, whereas ''facultative'' photoperiodic plants are more likely to flower under the appropriate light conditions, but will eventually flower regardless of night length.In 1920, W. W. Garner and H. A. Allard published their discoveries on photoperiodism and felt it was the length of daylight that was critical, but it was later discovered that the length of the night was the controlling factor. Photoperiodic flowering plants are classified as ''long-day plants'' or ''short-day plants'' even though night is the critical factor because of the initial misunderstanding about daylight being the controlling factor. Each plant has a different length critical photoperiod, or critical night length.Modern biologists believe that it is the coincidence of the active forms of phytochrome or cryptochrome, created by light during the daytime, with the rhythms of the circadian clock that allows plants to measure the length of the night. Other than flowering, photoperiodism in plants includes the growth of stems or roots during certain seasons and the loss of leaves. Artificial lighting can be used to induce extra-long days.=== Long-day plants ===Long-day plants flower when the night length falls below their critical photoperiod. These plants typically flower in the northern hemisphere during late spring or early summer as days are getting longer. In the northern hemisphere, the longest day of the year (summer solstice) is on or about 21 June. After that date, days grow shorter (i.e. nights grow longer) until 21 December (the winter solstice). This situation is reversed in the southern hemisphere (i.e., longest day is 21 December and shortest day is 21 June).Some long-day obligate plants are:* Carnation (''Dianthus'')* Henbane (''Hyoscyamus'')* Oat (''Avena'')Some long-day facultative plants are:* Pea (''Pisum sativum'')* Barley (''Hordeum vulgare'')* Lettuce (''Lactuca sativa'')* Wheat (''Triticum aestivum'')」の詳細全文を読む スポンサード リンク
|