This proves that there are indeed flowering stimulating substances transmitted between plants through grafting healing.
In addition, short-day plants after short-day treatment, such as high-cold vegetables, can be grafted on long-day plants, so that Babao can bloom under short-day conditions. On the contrary, if the long-day plants after long-day treatment are grafted on the short-day plants, the short-day plants can bloom under long-day conditions. This shows that the flowering stimuli produced by two plants with photoperiod response have almost the same properties. Treating petiole or stem with steam or anesthetic can prevent the transport of flowering irritants, indicating that the transport route is phloem. Chelaxuan of the Soviet Union called this stimulant forigen, but this substance has not been isolated yet. Photoperiodic induction: As long as plants get the right photoperiod for enough days, they can still bloom even if they are placed in an inappropriate photoperiod. This phenomenon is called photoperiodic induction.
The number of days (that is, several photoperiods) for plants to complete the photoperiodic induction varies from plant to plant:
Xanthium sibiricum: a photoperiod. That is, light 15 hours and darkness for 9 hours (15L-9D). Japanese Petunia: One day. The induction period of most short-day plants needs more than 1 day, such as soybean 3 days, hemp 4 days, red perilla 7-9 days, chrysanthemum 12 days, etc. It takes one day for diurnal plants: white mustard, spinach, rape, toxin, etc. More than one day: fairy: 2-3 days, quasi-southern cuisine for 4 days, annual beet 13- 15 days, etc.
The number of days required for photoperiodic induction of different plants is related to plant age, temperature, light intensity and day length. The plants are tender (reaching photoperiodic induction), and the induction period is shortened due to high temperature and strong light. ① Light intensity in photoperiodic induction: Under natural conditions, the light intensity required by photoperiodic induction is weak, far lower than that required by photosynthesis. It is generally believed that some plants are even lower in the range of 50 ~ 100 lux. For example, when rice is supplemented with light at night, the light intensity is only 8 ~ 10 lux, which can obviously stimulate the photoperiod response. It shows that the photoperiod response of plants is extremely sensitive to light.
② Dark-phase light blocking and physiological effects Dark-phase light blocking shows the relationship between photoperiod reaction and light intensity, light quality and substances involved in light reaction.
The dark period is more important for the flowering of plants. For short-day plants, their flowering depends on the length of dark period. As long as the dark period exceeds the critical night length (critical dark period), no matter how long the light period is, it will bloom. Therefore, it is more accurate to call short-day plants "night plants". On the other hand, diurnal plants do not need constant darkness. If the short-day plants are interrupted by a flash with a certain intensity in the middle of the dark period, then the short-day plants can't blossom, and the long-day plants can. This phenomenon is called light interruption in the dark period.
The experiment of interrupting the dark period with different wavelengths of light shows that red light is the most effective whether it is to inhibit the flowering of short-day plants or to induce the flowering of long-day plants. If far red light is used immediately after red light, the effect of stopping flashing will disappear during the dark period. It shows that photosensitizer is involved in the intermittent effect of flash in dark period. The maximum action spectrum of flash interruption effect in dark period is just the maximum absorption spectrum of photosensitizer, and the minimum action spectrum is just the minimum absorption spectrum of photosensitizer.
① Physical and chemical properties of photosensitive pigment
Phytochrome can be extracted from almost all parts of higher plants, that is, it exists in all tissues of higher plants (roots, stems, leaves, flowers, fruits, seeds, coleoptiles). In cells, photosensitizers may concentrate on the surface of cell membranes. The content of phytochrome is low in green tissue, but high in etiolated tissue, and the concentration level is 10-7— 10-5M.
High purity phytochrome has been prepared from etiolated monocotyledonous plant seedlings (corn, etc.). ). It was identified as a blue protein. Its chromophore is similar to chlorophyll and heme and has four pyrrole rings. But they are not cyclic, but open into a straight chain, which is connected with protein through covalent bonds, that is, they are composed of protein and chromophore. The molecular weight of natural phytochrome is about 120kDa.
② phytochrome and flowering induction
There are two forms of photosensitive pigments, Pr and Pfr. In etiolated tissues, most of the phytochrome exists as red light absorption type (Pr), and its absorption peak is at 660nm. When irradiated with red light, the absorption spectrum of Pr changes, and the absorption peak is at 725 nm. This shows that Pr is transformed into another form (Pfr) by red light irradiation.
At present, it is not clear how phytochrome produces physiological effects during flowering. Phytochrome itself is not a flowering stimulus, but it can trigger the formation (synthesis or activation) of flowering stimulus. It is generally believed that the flowering of short-day plants (SDP) and long-day plants (LDP) is related to the ratio of Pfr to Pr. For SDP, at the end of photoperiod, the Pfr/Pr ratio is high (because the proportion of red light is large during the day, which is beneficial to the formation of Pfr), and the synthesis of flowering stimuli is hindered. After the night, Pfr reversed to Pr, and the Pfr/Pr ratio became smaller. When this value reaches a certain level, it will trigger the metabolic process leading to the formation of flowering stimuli, and the flowering reaction of SDP can occur. If the dark phase is interrupted by red light, Pr will be converted into Pfr, and the Pfr/Pr ratio will increase, which will prevent the formation of flowering stimulation.
For LDP, the formation of flowering stimulation requires a high Pfr/Pr ratio, which can be obtained at the end of long light period. If the dark period is too long under short sunshine, Pfr will be converted into Pr, or Pfr will be destroyed, and the Pfr/Pr value will not reach a high level, and flowering stimulation will not be formed. The interruption of red light in the dark period can increase the Pfr/Pr value again, so that flowering stimuli can be synthesized and daytime plants can bloom.