a flowering Induction. Participation of phytochrome and hours

you are: a flowering Induction

Many developments which should proceed on exact ' to the seasonal schedule ', also depend on interaction between phytochrome and hours. These processes cover all life cycle of a green plant, including transition from vegetative growth to reproductive, formation of tubers, an induction of rest and ageing (fig. 12.10). The Most studied from these processes - a flowering induction.

For a long time it is noticed that the majority of plants at certain geographical width annually blossoms approximately at the same time - we have got used to that violets appear in the spring, roses - in the summer, and chrysanthemums - in the autumn. Flowering of these and many other plants is supervised by the photoperiod in which measurement participate both phytochrome, and rhythmic processes. to find out a role of each of them sensitive by the photoperiod of a plant placed for unusually long time in the darkness interrupted at a given time with short-term influence of red light. At korotkodnevnogo plants Chenopodium rubrum the irradiation red light in certain phases of the dark period promotes zatsvetaniju, and in other phases - suppresses it. It follows from this that depending on a phase of the dark period of Fdk can or favour zatsvetaniju, or it ingibirovat. Phases in which activating action of phytochrome of Fdk is maximum, will defend from each other on 24 ch, as well as phases of the greatest ingibirujushchego actions. It means that sensitivity to Fdk changes with okolosutochnoj periodicity.

The Induction of flowering at plants in the conditions of the normal 24-sentry sveto-temnovogo a cycle too is connected with a number of processes from which one are activated by Fdk, and others choke with it. The Time sequence and duration of these processes is regulated by internal clocks. At plants of short day which blossom when the length of the dark period becomes more critical, the reactions demanding high level of Fdk, proceed in the afternoon and in the beginning of night; the reactions proceeding is better at low levels of Fdk, begin during more later night time. earlier many physiologists thought that the critical length of the dark period is defined by speed of transformation of Fdk in Fk. However now this representation seems already incorrect. Apparently, the critical length of the dark period depends on duration of processes, ingibiruemyh phytolame Fdk which are in turn regulated by hours. Thus, we can see that photoperiodic measurement of time at plants of short day is connected not with phytochrome or hours separately, and with their interaction.

The Role of hours in an induction of flowering at a plant of long day is less clear. These plants if you remember, do not put flower kidneys until night will not be shorter than certain critical length. To some dlinnodnevnym to plants some hours of an irradiation distant red light (710-730 nanometers) too are necessary to high intensity during each 24-sentry of a cycle. Illumination in the afternoon shirokospektralnym a light source (for example, the sun) which lets out both distant red, and shorter light waves, quite effectively as well as the irradiation waves is shorter 700 nanometers in the afternoon after a long-wave irradiation at night. this requirement for long influence of intensive distant red light is a little similar to reaction to a high-intensity irradiation etiolirovannyh plants; probably that in both cases the big role plays ' krugoobrashchenie ' a pigment (I eat. gl. 11). However thus there is also an important difference: The irradiation etiolirovannyh the plants which had before illumination only Fk, distant red light raises level of Fdk whereas the similar irradiation of the plants which have been grown up on light, usually reduces level of Fdk. Thus, the requirement of plants of long day for strong illumination can be connected partially with requirement for Fk (or in low level of Fdk) throughout some part of a daily cycle.