Regulation of growth by light. Phytochrome opening

you are: Regulation of growth by light

The History of opening of phytochrome in the early fifties group of researchers of the Ministry of Agriculture of the USA makes one of the most exciting heads in the history of studying of plants. This history has begun approximately for 30 years earlier with work of two experimenters dealing with tobacco. U.Garner and X. Allard tried to multiply mutant type krupnolistnogo tobacco - Maryland Mammot who has casually grown in the single copy among other tobacco plants. During certain time the initial type has plentifully blossomed, and Maryland Mammot - is not present. Wishing to receive seeds of this valuable new type and being afraid that the plant can not blossom to autumn colds, scientists have decided to transfer it to a hothouse. However, despite all taken measures, a plant persistently remains in a vegetative condition approximately to the middle of December when on it there were rudiments tsvetkov - in some months after at normal plants formation of seeds has successfully come to the end.

The Analysis of various factors which could be responsible for this unusual behaviour, has resulted Garnera and Allarda in an inevitable conclusion that the plant has blossomed under the influence of very small length of day northern hemisphere before Christmas. They have established that flowering it is possible to cause carrying over of plants Maryland Mammot in special chambers with is artificial in the reduced light afternoon.

The Tobacco Maryland Mammot blossoming only in the event that length of day less of some critical size, began to name a plant of short day. Many other plants, including some forms of a soya, chrysanthemums concern this category and puansettii also. On the contrary, spinach and some grain blossom only when the length of day exceeds certain critical size; these are plants of long day. At last, there is a group of plants (tomatoes, etc.) which flowering does not depend on length of day (neutral plants). Reaction of plants to length of day is called fotoperiodizmom.

The Critical photoperiod for different kinds and even grades of plants both short, and long day considerably varies. It makes 14 ch for Biloxi - korotkodnevnogo the grade of a soya growing at width 35 ° whereas the grade of Batoravka which is usually grown up at width 45 ° and above, will blossom even at continuous illumination. These distinctions in the critical photoperiod play the important role in distribution of plants globe.

In the years which have followed opening fotoperiodizma, herd it is clear that many plants react to duration of continuous darkness, instead of for length of the light period. Differently, the so-called plant of short day is actually a plant ' long night '. For zalozhenija flower bugorkov certain minimum duration of the darkness which is not interrupted with light is necessary for it. Similarly the plant of long day can be actually a plant ' short night ': it will blossom only in the event that the night period not more long some maximum.

The Effective period of darkness for korotkodnevnogo can be made plants an inefficient way of simple dodge - to truncate it (all for some minutes) a little enough or to interrupt in the middle with flash of weak light. It means that the plant can ' measure ' duration of darkness to within several minutes and that fotoperiodizm is connected with work extraordinary sensitive svetovosprinimajushchej systems. The korotkodnevnoe plant durnishnik blossoms at a mode 15 ch light + 9 ch darkness, but will not blossom, if the dark period makes 8,5 ch or the 9-sentry the dark period interrupts the short light period (fig. 11.2). Only one suitable period of darkness can lead to flowering even if the subsequent dark periods are insufficiently long. This phenomenon is known as a photoperiodic induction. At many plants of long day back directed phenomenon takes place similar, but: Interruption of too long dark period by light flash leads to an induction and to zalozheniju tsvetkov.

Thus, plants of long and short day, probably, possess the similar photoperiodic mechanism, but last somehow operates divergently.

Korotkodnevnyj a grade of a soya of Biloxi so is sensitive to light that the inductive effect long temnovyh the periods can be removed even a minute irradiation by means of lamps nakalivanija (without the filter) in the middle of night. For this reason X. The Board-vik and S.Hendrix with employees have come to a conclusion that this plant would be ideal object for finding-out of a question on what lengths of waves most effectively prevent initsiatsiju flowerings; and these data in turn could help with identification fotoretseptornogo a pigment participating in the control of flowering. Therefore they have defined a spectrum of action for the given process, using big spektrograf for a simultaneous irradiation of groups of plants light with different length of a wave (fig. 11.3).

The Received spectra of action for flowering inhibition korotkodnevnyh plants of a soya and durnishnika and for flowering activation dlinnodnevnyh plants Hordeum (barley) and Hyoscyamus (henbane) have appeared amazingly similar (fig. 11.4).

In all cases the activity maximum in red area of a spectrum (about 660 nanometers) has been found out at almost full inefficiency of other areas. Similarity of spectra allowed to consider probable that zatsvetanie plants both short, and long day is supervised by the same pigment. The analysis of a spectrum of action has led to the assumption that the absorbing pigment is similar to a pigment of seaweed fikotsianinom, which rodstven to bilious pigments of animals. Unfortunately, authors have not found such pigments in the experimental plants and consequently began to conduct searches in other direction.

For a long time it was known that light strongly influences germination of some seeds. For example, the humidified seeds of salad of a grade the Grandee Slow motion sprout badly in full darkness, but quickly and well at exhibiting on - to light within several minutes. It has appeared that the spectrum of action for this effect is similar to a spectrum of action for flowering! To similarly it the sprout of the peas which have been grown up in full darkness, has very long, thin neligmentirovannyj the stalk bent apikalnyj a bend and almost not dismissed leaves. If such etiolirovannyj a sprout to expose only for short time for light, leaves after that are developed, the bend starts to be straightened and stalk lengthening is slowed down (fig. 11.5). The action spectrum is here again actually identical to a spectrum for flowering. It is necessary to conclude that such diverse reactions as germination of seeds, change etiolirovannogo a sprout (it ' deetio-ljatsija ') and a flowering induction, are regulated by the same pigment-receptor.

But what it for a pigment? The answer has been found in result of New interpretation of old experiences on germination of seeds of the salad spent to 1935 of L.Flintom and E.Mak-Alisterom. These researchers have shown that germination of seeds of salad the Grandee Slow motion not only is stimulated with red light, but also chokes with light of distant red area of a spectrum with length of a wave about 730 nanometers (fig. 11.6).

This opening has led to a hypothesis that red light changes a pigment in one direction, and distant red - in other. Experiences with consecutive influence red (and distant red light (recreation centres) have confirmed this hypothesis. In such conditions the seed reacted only to last irradiation as though the form of a pigment fixed at last exposition, was the unique effective factor (fig. 11.7).

Even the seeds irradiated of 100 times with Alternately red and distant red light, sprouted the same as and irradiated with that and other light one time. In all cases germination reaction was defined by last light influence previous darkness.

Then Bortvik and Hendrix have studied influence of distant red light on reactions of flowering and dietiolirovanija, caused by red light. Has been here again found out ' convertibility To - a recreation centre ' (fig. 11.8). It has allowed to foretell that there is one active pigment in two mutually photoreversible forms one of which is formed under the influence of red, and another - of distant red light (fig. 11.9).

Reversible, absorption shifts at 660 and 730 nanometers after an irradiation according to red and distant red light have given the chance to reveal easily a pigment and to measure its quantity, especially in etiolirovannyh plants where shielding by a chlorophyll does not create difficulties (see more low). Soon the pigment has been found out in extracts of plants, concentrated, cleared, will subject to the analysis and is partially characterised. It named phytochrome (from the Greek words meaning ' a plant ' and ' dye '). Its two forms have been named according to Fk (phytochrome,

Absorbing red light) and Fdk (absorbing distant red light). Phytochrome is synthesised in the form of Fk. Therefore etiolirovannye sprouts contain Fk, instead of Fdk. The irradiation red light transforms the phytochrome most part in Fdk - physiologically active form whereas the subsequent irradiation distant red light transforms Fdk back in Fk. (Fig. 11.10).