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Schematic diagram of apical dominance The phenomenon that the terminal buds of plants are long and the lateral buds are inhibited. (According to Cihai) The inhibitory effect of plant terminal bud growth on lateral bud germination and lateral branch growth (see the schematic diagram of terminal advantage in the figure), including the influence on the growth angle of lateral branches or leaves. According to the Encyclopedia of China, there is a close relationship between terminal buds and lateral buds in the process of plant growth and development. When the terminal bud grows vigorously, it will inhibit the growth of lateral buds. If the terminal buds stop growing for some reason, some lateral buds will grow rapidly. This phenomenon that the terminal buds grow first and the development of lateral buds is inhibited is called apical dominance.

catalogue

brief introduction

meaning

Genetic auxin theory

Nutrition theory

Nutrition transport theory

Brief introduction of application

meaning

Genetic auxin theory

Nutrition theory

Nutrition transport theory

App application

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Most plants have apical dominance, but the form and degree of expression vary with plant species. Plants with strong apical dominance have almost no branches, such as many varieties of sunflowers. Plants such as tomatoes have weak apical advantages and can grow many branches. The top advantage of shrubs is very weak, and there is almost no difference between trunk and branch. Most plants belong to intermediate types, such as rice and wheat. With the increase of distance, the inhibition degree of the top to the lateral buds decreased. Therefore, the inhibitory effect of lower lateral buds is lighter than that of upper lateral buds. Many trees have thus formed a pagoda-shaped crown. The difference of apical dominance and expression forms leads to the difference of plant growth posture. The apical dominance is also obvious in the growth of stolons, tubers, bulbs, bulbs and roots. The intensity of apical dominance varies with plant age, and is also affected by nutrition and environmental conditions. The top advantage of young plants is strong, but it is weakened when old plants are growing. The light intensity is too low, the soil is poorly ventilated or short of water, and the top advantage is enhanced; Nitrogen supply is sufficient, and the apical advantage is weakened.

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The number of plant lateral buds usually greatly exceeds the number of branches that can be maintained by water and organic and inorganic nutrients. The strength of apical dominance changes with the environment, which enables plants to adjust the number of branches according to the supply of water and nutrition, which is the main link for plants to regulate their own growth.

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At present, the cause of the phenomenon of "climax advantage" is still inconclusive. There are three main theories that can explain this phenomenon.

Auxin theory

Or auxin inhibition theory. Proposed by K.V. Timan and F. Schoug in 1933. Their experiments have proved that applying auxin to the cross section of broad beans after topping is the same as not topping. They believe that the terminal bud is the center of auxin synthesis, where the synthesized auxin is transported along the stem to the base, inhibiting the growth of lateral buds. This is the theory of auxin direct inhibition. Si Nuo proposed in 1937 that auxin does not directly inhibit the growth of lateral buds, but causes an indirect inhibition, which is the theory of auxin indirect inhibition. Apical dominance

This theory is also the most popular at present, and its experimental basis is the rapid growth of lateral buds after topping. If lanolin containing auxin is coated on the cut after decapitation, the lateral buds will not grow, that is, external auxin can replace the inhibitory effect of terminal buds on lateral buds. However, it was later found in lupine and other plants that the content of auxin in the lateral bud inhibited by the top was far below the optimal concentration required for the growth of the lateral bud. In recent years, it has been found that the inhibited lateral buds can grow (that is, the apical dominance is relieved) by applying cytokinin, so it is considered that the reason why the lateral buds are inhibited is that there is not enough cytokinin. Cytokinins are synthesized in roots, and the auxin produced by terminal buds may control the transport of cytokinins. Because of the high concentration of auxin in the terminal bud, it becomes the repository of input substances and obtains cytokinin before the lateral bud. Because of the low concentration of auxin, the lateral buds can't get enough cytokinin, and their growth is inhibited.

Nutrition theory

K was put forward by Gabel in 1900. He summarized the phenomenon of plant-related inhibition, and thought that cells grew rapidly and metabolized vigorously, and needed more nutrition. Because the terminal buds enjoy the nutrients transported by roots and leaves first, the lateral buds can't get enough nutrients, so the growth is inhibited.

Nutrition transport theory

F.W. Winter proposed in 1936 that the cells in the apical meristem are active in growth, metabolism and synthesis. The high concentration of hormones in the terminal bud promotes the transport of nutrients to the terminal bud, so that the lateral buds can not get enough nutrition and are inhibited. The relationship between the function of hormones and material transport in apical dominance phenomenon is quite complicated, and more than one hormone may include stimulation and inhibition.

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In agricultural production, in order to increase the yield and control the plant type of flowers and trees, the growth of crops, fruit trees and flowers and trees is often controlled by eliminating or maintaining the top advantage. Removing terminal buds to protect lateral buds, such as "topping" and "topping", can make plants branch more and bloom more. Topping is often used to remove apical dominance, so as to promote lateral bud germination, increase the number of lateral branches, or promote the growth of lateral branches. For example, for fruit trees, the tree shape can be expanded to produce more fruit branches; For tea trees and mulberry trees, the relatively low-lying lateral branches are easy to pick; For street trees, the shade area can be expanded. Some chemicals can eliminate the advantage of terminal buds, promote the growth of lateral buds and increase crop yield, and the effect is similar to that of cutting terminal buds. For example, triiodobenzoic acid (TIBA) has been successfully applied to soybean production. This method is called chemical topping.