Tsirkadnye rhythms. Whether it is valid rhythms endogenny?

you are: Tsirkadnye rhythms

Some authors believe till now that tsirkadnye rhythms are actually regulated not endogennymi, and any yet not revealed external factors. against this representation following facts most convincingly testify: 1) tsirkadnye rhythms remain and at the organisms quickly addressing round the Earth in artificial companions; 2) under constant external conditions duration of the period is not equal in accuracy to 24 hours. Under natural conditions exact periodicity ' is imposed ' by periodicity in surrounding conditions. It means that ' natural ' the period changes under the influence of any external signal, ' adjusting ' an internal rhythm to an environment rhythm a little. At the majority of organisms rhythms are corrected by daily changes of light exposure (fig. 12.2 see) and temperatures.

The Pigments serving by photoreceptors for updating of a rhythm, at different organisms are various. At many animal and some plants it is a pigment absorbing dark blue light, but at the majority of plants such role is played by phytochrome. Rhythms in these plants are corrected by transformation of Fk into Fdk. It would be possible to expect daily interconversions of Fk and Fdk in a vegetative fabric soon after rising and before a sunset. Apparently from fig. 12.6, the relation of energy of red light to energy of distant red light in solar beams about a terrestrial surface makes in the afternoon 1,3, but at a sunset quickly falls to 0,7.

It conducts to small decrease in the maintenance of Fdk which and further continues to decrease within night as a result temnovogo transformations of Fdk into Fk. In the morning, soon after sunrise, level of Fdk in process of increase in the mentioned parity of energy again raises. from this! It is clear, how increase of level of Fdk with sunrise could ' arrange ' internal clocks.