Photoperiodism

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Photoperiodism describes the dependence of growth, development and behavior in plants on the length of the day (photoperiod). The minimum power density is around 10 −2 down to 10 −3  W / m² - full moon light (≈ 5 · 10 −3  W / m²) can already be effective.

Short day plant (KTP) or long day plant (LTP)

In practice, this means a day-length dependence (daily light-dark period) of development processes in plants , in particular the flower induction (flower formation). The dark or night phase is decisive for the behavior of the plant. Photoperiodism is genetic. There are roughly three types of plants: short-day plants (KTP), long-day plants (LTP) and day- neutral plants . Short-day plants wait with the beginning or the intensification of a process, usually the formation of flowers, until the days (daily lighting duration) fall below a certain length of time. Plants that bloom with a daily illumination of less than twelve hours are called short-day plants and those that bloom with more than twelve hours of illumination are called long-day plants. Long-day plants wait with the beginning / intensification of about the bloom formation until the day length exceeds a certain number of hours.

This is not an all-or-nothing event, rather this reaction is more pronounced in different species . In some species thus reaches a single induction cycle ( Ipomoea nil ) , while others require up to 25 cycles ( Plantago lanceolata ) . A further distinction is made between qualitative (absolute) and quantitative short and long-day plants. The latter can be seen as a kind of intermediary link between the photoperiodic and the day-neutral plants, in which the duration of lighting has no influence on flower formation, as they bloom in both permanent darkness and permanent light, an extension (LTP) or shortening (KTP) However, the photoperiod leads to a strong promotion of the flower induction. In addition, there are short long day plants (KLTP) and long short day plants (LKTP) that require two successive photoperiods of different lengths. The purpose of this is to distinguish between short days in spring and autumn .

Detection of the length of the day

The length of the day is not recognized directly from the length of the photoperiod, but from that of the dark period, which also explains why a bright full moon night is enough to delay the induction of flowering in plants that are sensitive in this regard. In this context, one speaks of short or long night plants. With some KTPs, stray light from just one minute is enough to prevent flowering, whereas stray light with LTPs must be given for several hours to prevent flowering.

Furthermore, the area that is exposed to the light is almost completely irrelevant for the effect, since individual correctly exposed parts of a sheet are sufficient. At a rate of 2 to 4 mm / h, this information by means of the FT (Flowering Locus T) protein, which is also known as florigen is referred to the rung - meristems transported.

However, through experiments with grafting it was found that these systems are very similar or identical in many plants, since with grafted KTP leaves LTPs with short day lengths could be made to flower and vice versa.

Strategic sense

The meaning of this system is suspected in the range of different plants. At the equator there are mainly KTPs and day-neutral ones and at high latitudes more LTPs. B. the short vegetation window in summer must be carefully adjusted.

Examples

Qualitative long day plants

Quantitative long day plants

Day-neutral plants

Qualitative short day plants

Quantitative short day plants

Long short day plants

Short long day plants

See also

literature

Individual evidence

  1. ^ Photoperiodism . In: Lexicon of Biology . Spectrum of Science ( Spektrum.de [accessed on June 15, 2014]).
  2. ↑ Christel Kasselmann : aquarium plants. Ulmer Verlag, Stuttgart 1995; 2nd, revised and expanded edition 1999, ISBN 3-8001-7454-5 , p. 480.
  3. ↑ L. Corbesier, G. Coupland: The quest for-pile: a review of recent progress . In: Journal of Experimental Botany . tape 57 , no. 13 , 2006, p. 3395-3403 , doi : 10.1093 / jxb / erl095 .

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