The products and output of medicinal plants are formed through the development (growth and differentiation) of plant organisms. The development of plants is a very complicated life phenomenon. It is accomplished through the interaction between plant genetic material and internal and external conditions.
Here, genetic material is the basis of development, which stipulates the mode and temporal and spatial order of physiological metabolic reaction, and through it, the internal and external factors of cells can regulate the development of individual plants. The regulation of intracellular factors, including the regulation of gene activity and enzyme, will lead to the synthesis of specific protein or polypeptide (including the synthesis of enzyme protein). The regulation of intercellular factors is just like the regulation of plant hormones. Plant hormones are chemical messengers and play an important role in plant growth and differentiation. They can be transported from synthesis site to action site through plant vascular bundle system, which can activate genes and activate or inactivate enzyme activities. The regulation of external factors of cells includes the regulation of environmental factors such as temperature, light, moisture, CO2, O2 and mineral nutrition, so as to supply the materials and energy needed for plant nutrition and stimulate and induce the development process. These internal and external factors have a very subtle relationship of mutual coordination and restriction, and the change of any one factor will directly or indirectly cause the fluctuation of genetic gene activity and affect the development of plants.
Generally speaking, the growth and development of plants can be summarized as meristem and differentiation. Through cell meristem and expansion, plants can grow from small to large, from seedlings to plants. This irreversible increase in volume and weight is for growth. Cell differentiation leads to the transformation of plant structure and function from simple to complex, forming vegetative bodies such as roots, stems and leaves, from vegetative bodies to reproductive organs, flowers, fruits and seeds. This qualitative change process is for development. In the life process of medicinal plants, cell differentiation and differentiation are combined, but the conditions they need are different after all. Therefore, development and research are of great significance in the production of medicinal plants. Vegetative growth of medicinal plants, such as roots and rhizomes, whole grass, stems and trees, bark, etc. Whether it is intact or not has a great relationship with improving the output and quality of products. At the same time, vegetative growth is the basis of reproductive growth, and vegetative organs provide material and energy for the development of reproductive organs. Therefore, in order to harvest medicinal plants such as flowers, fruits and seeds used as medicines, more attention should be paid to the process of vegetative growth and qualitative change from nutrition to reproduction in order to obtain high-quality and high-yield economic products.
First, the life cycle of medicinal plants.
Plants feel the periodic changes of the external environment (such as day and night cycle, seasonal changes, etc.) through the rhythm of the internal "biological clock". ), and adjust their own physiological activity rhythm, so that it starts, goes on or ends in a certain period of time. If plants bloom in a certain season every year, it is because of the "biological clock". However, this endogenous rhythm should work at the same time as the periodic changes of the external environment, affecting the growth and development process or behavior of plants, thus strengthening or weakening them.
(A) the life cycle of plants
Generally speaking, the life of a plant is from the beginning of a fertilized egg to the formation of the next fertilized egg, or a plant begins with seed germination, goes through infancy, maturity, senescence and finally dies. This process is called the life cycle (life history) of plants. According to the difference of plant life cycle, it can be divided into:
1. Annual plants
The process from seed germination to flowering and fruiting to plant death, plants completed within one year, such as perilla frutescens, Schizonepeta tenuifolia, cassia obtusifolia, etc.
2. Biennial plants
Also known as perennial plants. Motherwort, Abelmoschus manihot, Euphorbia lathyrifera and other plants that grow nutritionally after their seeds germinate in the same year can only bolting, blossom, bear fruit and even die in the winter of the following year. The underground organs of many plants are formed by economic products of vegetative growth, such as Isatis indigotica.
3. Perennial plants
The life span is more than two years, forming a nutrition-reproduction cycle every year, and the growth and dormancy cycles alternate. The aboveground parts of herbaceous perennial plants die after flowering and fruiting every year, and the underground parts of perennial roots such as roots (ginseng), rhizomes (mint) or bulbs (Fritillaria), corms (saffron) and tubers (corydalis) can survive for many years. However, some perennial herbs, such as Ophiopogon japonicus, Evergreen, Ophiopogon japonicus, remain evergreen in winter. Perennial woody plants constantly increase their volume through the cambium at the top of growth cone or branch and root tip (or both) every year. Most plants can blossom and bear fruit many times in their lifetime; A few plants only blossom and bear fruit once in their lifetime, such as bamboo and agastaches; Other plants bloom several times a year, such as honeysuckle and plum twice.
(2) Individual growth of plants
There are many kinds of cultivated medicinal plants, most of which are seed propagation, and a considerable number of them are asexual propagation or both, such as Pseudostellaria heterophylla and Radix Rehmanniae. Sometimes it is difficult to distinguish between annual and biennial plants, or biennial and perennial plants. So, here is just a summary. The individual growth of plants is mostly from the beginning of seed germination to the re-acquisition of seeds, and some even get seeds year after year. In cultivation, the growth process of plants is divided into three growth periods.
1. Seed period
The stage from seed formation to germination is called seed stage. This period can be divided into three stages:
(1) embryonic development stage
This is the period of seed formation. From egg fertilization to ovule development into mature seeds. This period is completed on the mother, and there is a remarkable process of nutrient accumulation and synthesis, which is related to the growth and health of the mother and is easily influenced by the climate and environment at that time. Creating good water, fertilizer and photosynthetic conditions suitable for the growth of mother plants in cultivation management is the basis for promoting the robust development of seeds and the key to obtaining economic products of seeds.
(2) Seed dormancy period
Seeds have different degrees of dormancy after maturity and harvest. Because of the different types and characteristics of seed dormancy, some seeds have a long dormancy period, such as Coptis chinensis, Paeonia suffruticosa and Cornus officinalis. Some are shorter, such as safflower. The underground persistent organs of medicinal plants propagated by nutrition also have bud dormancy. For example, the bulbs of crocus sativus are dormant in summer, and during the storage of bulbs, leaves and buds differentiate. Therefore, in the storage and preservation of persistent organs such as seeds, attention should be paid to the regulation of adverse environmental conditions in order to promote the differentiation of buds of mature seeds and persistent organs and maintain their vitality.
(3) budding stage
After dormancy, the seeds and buds of vegetative organs can germinate or germinate under suitable conditions of temperature, moisture and oxygen (some plants also require light or dark conditions for seeds). During germination, nutrients stored in seeds or vegetative organs are transformed into structural substances of seedlings. The length of germination period varies greatly with different plant species. In this period, the most important thing is to provide suitable conditions for the germination of seeds and buds and the excavation of seedlings. Perennial woody plants germinate and grow new branches after dormancy in winter or summer.
2. Vegetative growth period
That is, the period of vigorous growth of vegetative organs such as roots, stems and leaves of plants. The germination of seeds into seedlings marks the beginning of plant autotrophic life. Photosynthesis of green leaves has become the main source of nutrition. The material and energy that seedlings get from the outside world are used for the growth of vegetative organs such as roots, stems and leaves and the accumulation of nutrients, which is manifested by the increase of plant dry weight, volume and height. The quality of vegetative growth is related to internal and external conditions. For example, it is controlled by growth regulators such as auxin, gibberellin and kinetin, and is influenced by sunlight, temperature, carbon dioxide supply, nutrition and moisture of minerals such as nitrogen, phosphorus, potassium, calcium and magnesium. Different plants have different requirements for fertilizer and water in different growth periods, so proper water and fertilizer management is an important field control measure. This period can be divided into three stages:
(1) seedling stage
The seeds germinate and enter the seedling stage. Which is the initial stage of vegetative growth. The nutrients produced by photosynthesis are not only consumed by respiration and metabolism, but also used for the growth of roots, stems and leaves. During this period, the seedlings grew rapidly, their metabolism was vigorous and their adaptability to temperature was weak. Some plant varieties still need proper shading to prevent strong light, such as ginseng, coptis, notoginseng and so on. Although the amount of soil moisture and nutrients absorbed by plants at seedling stage is not much, the requirements are very strict. Seedling has a great influence on future growth and development, so it is necessary to strengthen seedling management, arrange seedling in a suitable season, and ensure that organs of economic products grow at a suitable temperature. Perennial plants began to sprout new seedlings and branches at this time, and turned green quite early.
(2) vigorous vegetative growth period
After the seedling stage, plants began to grow vigorously. According to its genetic pattern and sequence, vegetative organs with different shapes and structures were constructed. The branches, leaves and roots of annual plants grow vigorously, which lays a nutritional foundation for flowering and fruiting. The assimilates (photosynthetic products) of perennial plants have been used for the growth of roots, stems and leaves, and gradually turned into the stage of nutrient accumulation, forming tubers, tubers, bulbs, corms and other organs, such as Radix Curcumae, Rhizoma Pinelliae, Fritillaria, Crocus sativus, etc. In cultivation, we should arrange this period in the most suitable environment for nutrient accumulation, or create conditions suitable for high yield.
Woody plants, the time from seedling growth to flowering varies, 1-2 years, such as Lycium barbarum; Older people can reach several years to more than ten years, such as Eucommia ulmoides, Magnolia officinalis and Cornus officinalis. The vegetative growth of this plant becomes a growth cycle every year.
(3) dormant period
Biennial and perennial herbs, after the formation (including expansion) of vegetative storage organs, the aboveground organs gradually wither or stagnate and enter dormancy, which is not suitable for the external environment, such as Fritillaria. In cultivation, this period is often associated with harvested products, so it is necessary to apply good storage methods or protective measures to make them spend hot or cold seasons and minimize the consumption of nutrients during storage to meet the needs of germination or bolting, flowering and fruiting in the coming year. This dormancy and seed dormancy are different in nature, and most of them are forced dormancy.
Several vegetative growth periods of plants are closely related and inseparable, and each growth period lays the foundation for their longevity. But not every plant has these three growth periods. For example, annual medicinal plants have no dormancy period of vegetative organs.
3. Reproductive growth period
On the basis of vegetative growth, plants not only increase in size and weight significantly, but also undergo a series of physiological and biochemical changes, turning to reproductive growth, that is, budding, flowering, fruiting and seed formation. This period can be divided into three stages:
(1) flower bud differentiation stage
Flower bud differentiation is a turning point from vegetative growth to reproductive growth. When a plant grows to a certain period, some factors in the external environment, such as the seasonal changes of sunshine and temperature, can toggle the "biological clock" in the plant, induce the metabolic type of the apical meristem of the plant to change, make its shape and structure change accordingly, and make the growth cone differentiate into flower buds and enter reproductive growth. Then it will sprout and blossom. For example, the flower bud differentiation of crocus sativus bulb is carried out during summer storage. First assimilate leaves from flower buds, and then start flower differentiation. According to the order of bud leaves, flower primordium, perianth, stamen, pistil and large and small spores, flower organs are formed from outside to inside. Temperature is the main inducing factor in the process of flowering. Different plants have different flower bud differentiation periods and ways, and the length of their pregnant buds is quite different. Some plants can last for more than a year, and buds can be seen with the naked eye, such as Cornus officinalis. Generally speaking, during flower bud differentiation, stems, leaves and roots grow simultaneously. In training, we should try our best to create a suitable environment and promote development.
(2) Flowering period
From budding to pollination and fertilization, it is sensitive to temperature, light and water. Too high or too low temperature and drought, as well as insufficient light, will affect the opening of flowers.
(3) fruiting period
After flowering and fertilization, the ovary expands to form fruits and seeds. This is an important period for producing fruit and seed economic products. In cultivation, this period should be arranged in the most suitable season, and water and fertilizer should be supplied in time to facilitate the normal growth of fruits and vegetative organs, so that nutrients in stems and leaves can be input into fruits and seeds. On the one hand, most perennial herbs blossom and bear fruit, on the other hand, they still have vigorous vegetative growth and form storage organs. At this time, appropriate promotion and control measures should be taken according to the training purpose.
It should be pointed out that not every plant has these periods. The vegetative growth and reproductive growth of many plants alternate or overlap with each other. The growth process of some plants is quite special and cannot be summarized by the above periods. For example, some plants are mainly cultivated through asexual reproduction, and their individual development is not a new beginning, but a continuation of maternal development. Although it will also blossom and bear seeds, it is not the same as sexual reproduction.
Second, the growth cycle of plants.
In the evolutionary history of phylogeny, plants adapt to the external environment for a long time, thus forming a variety of cyclical rhythms in plant growth, such as seed dormancy, bud germination and so on. This rhythm is called periodicity. The time and speed of the individual growth process of plants are also obviously synchronized with the periodic changes of environmental conditions, such as germination, growth, budding, flowering, fruiting, fruit ripening and other processes, all in a certain order. These periodic manifestations are closely related to the formation of reproductive organs, the composition, yield and quality of economic products. Grasping the periodic law of plant growth in cultivation is conducive to formulating various cultivation measures according to local conditions. Only three main growth cycles are described here.
(1) annual growth cycle
Plants adapt to the rhythm of climate change (seasonal change) for a long time, forming an annual growth cycle. In nature, most temperate plants germinate and grow when the temperature rises in spring, and then flower buds appear; Flowering, fruiting and fruit ripening under high temperature in summer and autumn; In late autumn and early winter, when the temperature is low, the leaves fall off or wither and enter the dormant period. Although the phenology of various plants growing in various places is early or late, they all have their own annual growth cycle rhythm. This rhythm, whether in the growth of cell number, the weight of the whole plant, the elongation of stems, the expansion of leaf area or the development of fruits, the increase of product organs, or even the change of body content, shows a * * * feature, that is, the initial growth or accumulation is slow, then it reaches the highest value with the gradual acceleration of plant growth process, and then the growth or accumulation speed gradually slows down or even stagnates. This slow-fast-slow basic law of plant growth is called annual growth cycle or large growth period. The "S" curve plotted with the test data is called the long-period growth curve (Figure 4- 1).
Fig. 4 ——1plant growth curve
On the basis of observing the annual growth cycle of plant organs and product inclusions, according to the expected cultivation purpose, before the fastest growth period of plants or organs comes, reasonable technical measures are taken to regulate the growth process and speed of plants and obtain ideal economic yield. These periodic laws can also be used to reasonably arrange intercropping, determine sowing time, and make plants make full use of sunlight and soil fertility.
(2) Daily growth cycle
The growth rate of plants includes not only the annual growth cycle that adapts to seasonal changes, but also the daily growth cycle that adapts to daily diurnal changes. The growth factors of plants mainly include temperature, light and water in the body. During the growth of a day, plants go through day and night, which is inevitably influenced by the growth factors of circadian rhythm, showing periodic changes. In the daily growth cycle, the growth rate of plants is most closely related to temperature. Generally speaking, under the condition that plants are not short of water, proper high temperature during the day is beneficial to enhance photosynthesis, while proper low temperature at night weakens plant respiration, reduces the consumption of photosynthetic products and increases net accumulation. When plants are short of water, the growth rate will decrease at noon, and there will be two growth peaks before noon and at night in a day. Plants grow fastest at night only when there is a serious shortage of water during the day. Therefore, in the circadian rhythm of a certain temperature level, the greater the temperature difference between day and night, the higher the yield and the better the quality of plants. The diurnal cycle characteristics of plant growth are related to the circadian temperature rhythm of origin.
(3) culture cycle
Plant cultivation cycle refers to the planting period and period determined according to the biological characteristics of various plants and the requirements of environmental conditions under certain natural geographical environment conditions, as well as the economic products needed for artificial cultivation purposes. The concepts of plant cultivation cycle and life cycle are different. The roots of cultivated plants are the result of long-term planting and selection from the wild state, and have become the current cultivated state and good economic characters. The whole growth period of cultivated plants and wild species will be different, and their adaptability will be different. The geographical location and ecological environment of the introduction place and origin (main origin) will cause the change of cultivation cycle. Some plants need to shorten the growth period from perennial to biennial or annual according to the quality of economic products in introduction and cultivation, such as aster. The culture cycle generally has obvious regional characteristics. Due to the wide variety of medicinal plants, different organs and parts of economic products, diverse propagation methods and obviously different cultivation periods. Due to the limitation of natural climatic conditions, the growth period of some herbs has changed. The same herbs are cultivated perennial in warm areas, but they may be cultivated annually or biennially in cold areas, such as andrographis paniculata and fennel. Even in the same area, due to different cultivation purposes, the cultivation years are different. For example, the roots (Radix Isatidis) and leaves (Folium Isatidis) of Isatis indigotica in biennial plants are medicinal, so they are only cultivated as annual plants in production, sowing in spring and harvesting in autumn. This can make full use of the suitable natural growth season, maintain a long vegetative growth time, promote the growth of roots and leaves, and obtain high-quality economic products. If seeds need to be obtained, they should be sown in autumn to meet the requirements of low temperature at seedling stage and complete the vernalization process. In the second year, they will bolt, blossom and bear fruit and be cultivated once every two years. In order to reduce the impact of diseases on yield, the cultivation cycle can also be changed. For example, foxglove is a perennial herb, its leaves are used as medicine and its properties are mild. High temperature and humidity are not conducive to plant growth. Whenever the rainy season is concentrated in summer, the root rot is serious and the mortality rate is high, which leads to a large number of plants shortage in the field. Although the content of glycoside per plant is high, the total yield of glycoside is not high due to the shortage of plants. Therefore, it is often changed from three years to two years, and the spring sowing seedlings are changed to autumn sowing seedlings, and the leaves are harvested in the next summer. The yield of plants in the field is ensured, and the yield of leaves is also improved. Although the glycoside content in the leaves of a single plant is slightly lower than that of a three-year-old plant, its total glycoside content is much higher than that of a three-year-old plant, which has achieved results. It can be seen that the cultivation cycle of plants can be adjusted according to different cultivation objects and purposes through cultivation measures adapted to local conditions. Especially with the development of modern science and technology, artificial can create various conditions suitable for plant growth and development, promote cultivation and shorten the cultivation cycle.
Third, the conditions from vegetative growth to reproductive growth
Among the cultivated objects of medicinal plants, most species are harvesting their roots, stems, leaves, skins or whole grass; Others collect flowers, inflorescences, fruits or seeds. Therefore, in order to improve the yield and quality in cultivation, it is sometimes necessary to promote the flowering of plants, and sometimes it is necessary to delay the flowering or even not to bloom. And such requirements are closely related to flowering. Generally, when the vegetative growth of plants reaches a certain physiological state or a certain age, it will turn into reproductive growth. This is determined by the genotype of the plant. When plants are induced by suitable external conditions, the stem growth cone begins to differentiate into flower buds, and morphological and physiological changes occur. The flower primordium is formed at the position where the Ye Yuan primordium was originally formed, and then the flower primordium splits into various parts of the flower, and finally the reproductive organs (flowers) are formed. Usually flower bud differentiation is the turning point from vegetative growth to reproductive growth. The appearance of reproductive organs (flowers) marks the great changes in morphological structure, physiological function and genetic information during the individual development of plants. This change is based on vegetative growth, which is far more complicated than vegetative growth and requires more stringent external conditions. Now the main external conditions are light and temperature; The internal conditions are hormones and nutritional status in the body.
(A) the external conditions for inducing flowering
1. Photoperiod phenomenon
Photoperiod refers to the relative alternating length of day and night. The photoperiod at different latitudes on the earth varies seasonally (Figure 4-2).
Figure 4-2 Sunshine Length at Different Latitudes
(1) Photoperiodic Reaction Types
The ratio of light to dark in a day and night has an important influence on the development of plants, especially on the formation and flowering of induced buds. The response of plants to the relative length of day and night is called photoperiod phenomenon. This is because plants have adapted to the sunshine conditions in the growing season of their origin in the long history of systematic development. Therefore, the response of various plants and varieties to photoperiod is very different. According to the different responses of plant flowering to photoperiod, medicinal plants can be divided into three types:
(1) Perennial plants bloom or promote flowering under the sunshine length (critical day length) longer than a certain period of time; However, it does not bloom or delay flowering under short sunshine, such as scopolamine, Sedum, mustard seed, fennel, gardenia, pyrethrum and so on.
② Short-day plants, such as chrysanthemum and xanthium sibiricum. Perilla frutescens, Petunia Petunia and Rehmannia glutinosa can promote flowering when the sunshine length is shorter than a certain time (critical day length), and will not bloom or delay flowering when the sunshine is longer.
(3) Chinese and Japanese plants are not strict about the length of sunshine, and have a wide range of adaptation to photoperiod, and can bloom under longer or shorter sunshine, such as Euphorbia peltata, Impatiens, Catharanthus roseus, Achyranthes bidentata, Lonicera japonica, Pinellia ternata, etc.
There are also some plants that need double sunshine conditions, such as the short-day plant Vasong, which must bloom for a short time and then for a long time.
(2) Critical day length and critical night length
The difference of photoperiod between long-day plants and short-day plants is not defined by the light and dark signal of 12 hour, nor is it reflected by the absolute value of sunshine length, but depends on the response of each plant to the critical day length and critical night length. Every factory has a minimum or maximum critical value of sunshine requirements. The minimum sunshine length (lower limit) leading to flowering of perennial plants is called critical day length; The maximum day length (upper limit) that causes ephemeral plants to bloom is called critical day length. According to the above concepts, it is used to distinguish the two. Perennial plants bloom or promote flowering when the day length is longer than the critical day length. For example, the critical day length of a fairy is 1 1 hour, and that of a hibiscus is 12 hour. Short-day plants bloom or promote flowering when the day length is shorter than the critical day length. For example, the critical daily length of Xanthium sibiricum and Chrysanthemum morifolium is 15 hours. Plants in China and Japan have no critical day length and can bloom all year round.
In nature, day and night always appear alternately in a 24-hour cycle. Corresponding to the critical day length is the critical night length. Critical night length refers to the minimum dark period length for short-day plants to bloom or the maximum dark period length for long-day plants to bloom. The critical night length is more important to flowering than the critical day length. Therefore, short-day plants are often called night plants, and long-day plants are called short-night plants.
(3) Induction time and position of photoperiod
The so-called photoperiodic induction refers to the appropriate photoperiod acting on plants, thus causing flowering reaction. The part that feels the photoperiod signal is the leaf, and the part that induces flowering is the growth cone (meristem) of the stem tip. After the leaves feel the photoperiod effect, they produce flowering stimuli (possibly hormones), which are transferred to the growth cone to cause flower bud differentiation. Whether the plants with short or long sunshine feel the effect of photoperiod signal, it is not when the seeds germinate, but when the plants reach a certain physiological age or grow to a certain size, they will produce photoperiod response. For example, kenaf is sensitive to photoperiod response only when it is near the 6-leaf stage. Generally speaking, the older plants are, the more sensitive they are to the photoperiod. The sensitivity of immature leaves and mature leaves is small, and the sensitivity of leaves is the strongest around the complete jointing stage. Various plants are sensitive to photoperiod at different ages.
The number of days of photoperiod (sunshine length) induced by plants varies with plant species, age, sunshine length, illumination and external temperature, for example, the induction days of perennial plants are 2-3 days. Short-day plants such as Xanthium sibiricum and Chenopodium album can bloom in 5-8 days after receiving 10- 16 hour photoperiod (long dark period). Some plants have completely different photoperiod effects at different temperatures. For example, morning glory is a short-lived plant at higher temperature, but it becomes a long-lived plant at lower temperature. Under natural conditions, long-day high temperature in summer and short-day low temperature in winter always accompany each other. In the physiological sense of flowering, high temperature is equivalent to light, and low temperature is equivalent to darkness. These two factors should be coordinated with the biological characteristics of crops under cultivation.
2. Temperature sensing
The temperature changes in nature are always seasonal and diurnal. Plant life has also adapted to these two periodic changes. The growth rate of plants also changes during the day, and the growth rate is the fastest at night and in the morning. Because the temperature is high during the day and low at night; There is sunshine during the day, photosynthesis is vigorous, and there is no photosynthesis at night, but it still has breathing function. If the temperature is low at night, the consumption of photosynthetic products by breathing can be reduced. Therefore, the periodic changes of hot days and cold nights in a day are beneficial to the growth of plants. For example, the daily range of tropical plants should be 3-6℃; Temperate plants are at 5-7℃, and desert plants are more than 10℃. The response of plants to periodic temperature change signals is called temperature cycle phenomenon. Temperature period and photoperiod are always closely related. Plants respond to day and night light intensity, and also to day and night temperature changes. For example, scopolamine must have a temperature of 28.5℃ in addition to a certain photoperiod to induce flower formation.
In the process of flower formation, flower induction and flower organ formation are two processes. Therefore, when plants are induced by certain environmental conditions (mainly photoperiod and temperature), the flowering process itself needs suitable external environmental conditions. Only in this way can the whole flowering process be completed and the quality and quantity of flowers be guaranteed.
(1) low temperature induction
The formation of flowers is not only affected by photoperiod, but also by temperature induction. Some biennial medicinal plants sown or planted in autumn and winter, such as Isatis indigotica, Arctium lappa, etc., spend the cold winter at the seedling stage, experience the low temperature period in the following spring, bolting and flowering, and bear fruit in summer and autumn. Low temperature is a necessary condition for inducing flowering of this kind of plants. The phenomenon that plants need a certain period of low temperature to blossom and bear fruit is called vernalization. Artificial methods are used to meet the low temperature requirements of plants and make them complete the vernalization process, which is called vernalization treatment. Some perennial herbs can also promote flowering through vernalization. For example, when Angelica sinensis is planted at a low temperature of 4-4℃ 150 days, its bolting rate can reach 96- 100% (Wang Wenjie). For plants with strong winterness, the lower the vernalization temperature, the longer the vernalization time. However, it must be pointed out that when the vernalization process is not completed, if the plants are restored to normal temperature, the effect of low temperature induction will disappear, and the so-called vernalization removal must be repeated to be effective.
In addition, there is a phenomenon of inducing flowering from low to high and then to low in perennial medicinal plants. For example, it takes more than one year for the flower buds of Cornus officinalis to differentiate into flowers.
(2) High temperature induction
Among medicinal plants, some plants need high temperature induction to bloom. Crocus sativus, for example, is a perennial plant with sexual abortion, vegetative propagation of bulbs, long leaves in spring, dormancy in summer, and regenerative flowering of bulbs in autumn. During the dormancy of bulbs in summer, a series of physiological, biochemical and morphological changes occurred in vegetative bodies, completing the morphogenesis process of reproductive organs such as leaf differentiation, flower bud differentiation and flower organ formation, and it did not bloom until autumn. Studies have confirmed that the change of bulb storage temperature plays an important role in inducing the formation of reproductive organs (flowers) of crocus sativus. In the process of flower bud differentiation to flowering, the temperature changes from high to low. The optimum high temperature is 28℃ and the critical low temperature is 15℃. The early or late appearance of high temperature not only affects flower bud differentiation, but also affects the early or late flowering. After flower bud differentiation, it needs a certain low temperature condition to bloom and grow normally. On the contrary, the high temperature in the late stage of flower bud differentiation not only makes the flowers shrink and retreat, but also inhibits flowering and delays flowering. This is obviously influenced by the temperature and precipitation rhythm of the plant's origin climate (Mediterranean coast), so natural regeneration is carried out to adapt to and spend the hot and dry summer, while maintaining the temperature cycle rhythm formed in the past. Another example is Aster.
(3) Induction period and position of temperature
The parts that feel the temperature are diverse, which are different from those that respond to the photoperiod. The influence of temperature on flower induction can generally be seen in seed germination, seedlings or dormant buds, dormant storage organs (such as tubers, bulbs, bulbs, etc. ) and other parts where plants grow. The parts that feel the temperature at seedling stage are mainly the growth cone of the stem tip, but some of them are roots and leaves. Seedlings must reach a certain size (young age), have a certain amount of growth (stem diameter, number of leaves) and weight in order to pass vernalization reaction. Without a certain amount of growth, even if it encounters low temperature, it is difficult to show the effect of vernalization treatment, such as foxglove, angelica sinensis and angelica dahurica. Temperature sensing is also related to the size or weight of the storage organ.