Photoperiodism

Photoperiodism includes all Morphosen of plants, depending on the duration of the photoperiod ( light period ) are induced. The threshold energy is then about 10-2 to 10-3 W/m2 [ it may already full moon light (~ 5 x 10-3 W/m2) be effective ].

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

In practice this means one day length dependence ( daily light-dark cycle) of developmental processes in plants, especially the flowering induction ( flower formation ). The dark or night phase here is crucial for the behavior of the plant. Photoperiodism is genetic. It can roughly distinguish three types of plants: short-day plants (KTP ), long-day plants ( LTP) and day-neutral plants.

This is not an all-or -nothing event, this reaction is rather different pronounced in different species. Thus, in some species reaches a single induction cycle ( Ipomoea nil ), other need, however, up to 25 cycles ( Plantago lanceolata). There is a further distinction between qualitative ( absolute ) and quantitative near-or long-day plants. These can be viewed as a kind of mediating link between the photoperiodic and the neutral plants because they bloom in both permanent darkness and in continuous light, an extension ( LTP) or shortening ( KTP) of the photoperiod, however, but a strong promotion of floral initiation result has. Moreover, even Kurzlangtagpflanzen ( KLTP ) and Langkurztagpflanzen exist ( LKTP ) that require two different lengths consecutive photoperiods. This has the sense to distinguish between short days in spring and autumn.

The distinction between KTP and LTP, however, has less to do with the respective day length than with the direction from which the critical day length is exceeded. So bloom LTPs, when the days finally long enough and KTP when the days finally are short enough. Since the critical day length is species-specific, it may well be an overlap here.

Recognition of daylength

The day length is not recognized, however, directly over the length of the photoperiod, but over which the dark period, which explains why a bright full moon night already sufficient to delay the induction of flowering of sensitive plants in this regard. One speaks in this context of short - or long- night plants. Some KTP stray light is already enough from just one minute to prevent the bloom, whereas stray light at LTPs must be given over several hours to reach a flower induction.

Furthermore, the surface which is exposed to light, almost irrelevant to the effect, as already sufficient individual properly exposed portions of a sheet. At a rate of 2 to 4 mm / h, this information is by means of FT ( Flowering Locus T ) protein, which is also referred to as florigen, transported to the shoot meristems.

Through experiments with grafts was found, however, that these systems in many plants very similar or the same, as could be brought with grafted KTP leaves LTPs with short day length to flower, and vice versa.

Strategic sense

The purpose of this system is justified in the area of ​​distribution of various plants. To be found at the equator mainly KTP and day-neutral and at high latitudes rather LTPs, as in this example, the short growing time windows must be well-timed in the summer. Even in areas where there is drought or other adverse weather events, these systems are calibrated out.

Examples

Qualitative long-day plants

Quantitative long-day plants

  • Arabidopsis thaliana
  • Solanum tuberosum

Day-neutral plants

  • Poa annua
  • Thlaspi arvense
  • Helianthus tuberosus
  • Senecio vulgaris

Qualitative short day plants

Quantitative short-day plants

Langkurztagpflanzen

Kurzlangtagpflanzen

Range (biology) Timothy-grass Soybean Bryophyllum daigremontianum Bolting (horticulture) Eduard Strasburger
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