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.