What is the photoperiod phenomenon?

The response of an organism to changes under sunlight, especially the photoperiod phenomenon manifested by biological processes.

The phenomenon that plants control flowering by feeling the change of day and night is called the response of flowering to the relative length of day and night. Some people have given a broad definition of photoperiod phenomenon, which means that plants control their physiological reactions by feeling the length of day and night. The phenomenon that plants control flowering by feeling the change of day and night is called the response of flowering to the relative length of day and night. Some people have given a broad definition of photoperiod phenomenon, which means that plants control their physiological reactions by feeling the length of day and night. The phenomenon that plants control flowering by feeling the change of day and night is called the response of flowering to the relative length of day and night. Some people have given a broad definition of photoperiod phenomenon, which means that plants control their physiological reactions by feeling the length of day and night. The phenomenon that plants control flowering by feeling the change of day and night is called the response of flowering to the relative length of day and night. Some people have given a broad definition of photoperiod phenomenon, which means that plants control their physiological reactions by feeling the length of day and night. The discovery of photoperiod was made by Ghana and Allard in the United States. 19 10, Ghana and Allard worked in the Batesville Agricultural Experimental Station of the US Department of Agriculture in Maryland, USA. They found two unexplained phenomena. One is Maryland mammoth, a tobacco variety, which can reach 3-5 meters in summer, but does not bloom. If the plant height in the greenhouse is less than 1 m in winter, it can bloom. Another phenomenon is that a soybean variety is sown at different times in spring, but it blooms at the same time in summer, although the vegetative size of soybean is different at different sowing dates. The above phenomenon shows that plants bloom in a specific season, and they think that there must be some environmental factors controlling flowering. As we all know, the main environmental factors are temperature, light, moisture, gas and mineral nutrition, so temperature and sunshine length are the main factors that change with the seasons. Therefore, they tested the influence of sunshine length on tobacco flowering, and found that only when the sunshine is shorter than 14 hours, tobacco will bloom, otherwise it will not bloom. Later, it was found that many plants need a certain length of sunshine to bloom, such as winter wheat, spinach, radish, pea, cactus and so on. This is the discovery of photoperiod phenomenon. Edit this paragraph 1 for plant photoperiod response type, short-day plants.

In the 24-hour day and night cycle, plants that bloom only when the sunshine time is shorter than a certain number of hours. Such as American tobacco, soybean, rice, corn, millet, chrysanthemum, xanthium and so on.

2. Perennial plants

A plant that blooms only when the sunshine time exceeds a certain number of hours in a 24-hour day and night cycle. Such as barley, wheat, rye, radish, spinach, Chinese cabbage, Chinese cabbage, fairy, beet and so on.

① Plants with absolute long sunshine or absolute short sunshine

24-hour flowering has a clear critical day length, that is, the limit sunshine length required for flowering. Plants that can't bloom when sunshine hours exceed this critical day length are called absolute short-day plants, while plants that can bloom when sunshine hours exceed this critical day length are called absolute long-day plants.

Corresponding to the critical day length is the critical dark period. Critical night length refers to the minimum dark period length of short-day plants flowering or the maximum dark period length of long-day plants flowering in the day-night cycle.

Table: Critical day length of some absolute short-day plants and absolute long-day plants

Plant name Photoperiod type Critical day length in 24-hour day and night cycle (hours) Beijing soybean (medium-ripe) short-day plant 15 poinsettia short-day plant 12.5 American tobacco short-day plant 14 Xanthium sibiricum short-day plant 15.5 day fresh (28.5℃) long-day plant/

For example, in the above table, the critical daily length of soybean flowering in Beijing is 15 hours, which means that if it exceeds 15 hours, the flowering reaction will be affected. Then its corresponding critical night length is 9 hours. In other words, the night should not be shorter than 9 hours, otherwise it will affect flowering. Perennial plants are the opposite.

In a sense, the critical night length is more important to flowering than the critical day length. Long night induces short-day plants to bloom, but inhibits long-day plants to bloom. Therefore, short-day plants are also called night plants. Diurnal plants are called short-night plants.

② Plants with relatively long sunshine or relatively short sunshine.

There is no absolute critical day length for flowering of many short-day plants and long-day plants. Under the unsuitable sunshine length, they can hardly become flowers after a long time. For example, Xanthium sibiricum is a relatively short-day plant.

3. Japanese neutral plants (DNP)

The flowering of these plants is not affected by the length of sunshine, and they can bloom normally under any sunshine. Such as cotton, tomatoes, eggplant, green beans and some perennial flowers (roses).

4. Short-day plants and long-day plants

In this kind of plants, the two processes of flower induction and flower formation need different sunshine lengths. For example, the rooting of big leaves and the attraction of fragrant trees all need long sunshine. After that, if you continue to grow in long sunshine, you can't form flower organs, but you can only bloom in short sunshine. This plant is called a diurnal plant. Campanula platycodon grandiflorum and Pinus elliottii are just the opposite. The induction of flowers is completed under the condition of short sunshine, while the formation of flower organs needs long sunshine. This plant is a short-day plant. Geographical latitude and photoperiod response types Edit The different types of photoperiod response of plants in this section are the result of long-term adaptation to the environment. Due to the different photoperiods at the same latitude, different seasons and different latitudes in the same season, the regular distribution of plant photoperiod response types has been formed.

China is located in the northern hemisphere, and the temperature is low in short days in spring, so plants are generally in the seedling stage and have nothing to do with flowering for the time being. The temperature is high in autumn, which is suitable for plant growth, so the sunshine at this time will significantly affect the flowering of plants. In summer, the natural sunshine time is long and the temperature is high, which is a suitable period for plant growth and development. In a year, it is basically these two seasons that affect the flowering and fruiting of plants. In low latitudes, the temperature is very high all year round, but there is no condition for long sunshine, so plants with only short sunshine usually germinate in early spring and bloom at any time in summer and autumn. Some plants can have multiple seasons, such as rice; In mid-latitude areas, there are both long and short sunshine conditions, and the temperature is high in autumn, so plants with long and short sunshine are distributed. Long-day plants bloom in late spring and early summer, and short-day plants bloom in autumn; In high latitudes (Northeast China), although there are days, the seasonal variation of temperature is obvious. When the sunshine is short in autumn, the temperature is already very low and plants can't grow. Therefore, some plants that need longer sunshine cannot survive. The mechanism of photoperiod induction is edited in this paragraph 1. Feel the part of the light cycle.

Experiments show that the part that feels the photoperiod response is the leaves of plants: for example, experiments are carried out with chrysanthemum, a short-day plant. First, all the leaves at the top of the plant are removed.

2. The conduction of flowering stimuli

The part receiving photoperiodic induction is the leaf, and the part undergoing photoperiod reaction is the growing point of the stem tip. There is a petiole and a stem between the leaf and the reactive part. Then, there must be a problem of flowering stimulation conduction. Take the grafting experiment of Xanthium sibiricum as an example. Five plants of Xanthium sibiricum were grafted with each other, and only one leaf on one plant was in the photoperiod suitable for Xanthium sibiricum flowering (short sunshine), while the other plants were in the photoperiod unsuitable for Xanthium sibiricum flowering (long sunshine), so they could all blossom.

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.

3. photoperiodic induction

Photoperiodic induction: As long as plants don't get enough suitable photoperiod, they can still bloom even under unsuitable 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.

4. Dark light interruption phenomenon

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.

5. Photosensitive pigment and its role in flower formation

The maximum action spectrum of dark flash interruption effect 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 ring-linked, but open into a straight chain, which is connected with protein by a valence bond of * * *, 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. Quote /view/70526 1.html to edit this paragraph? fromTaglist