In the process of plant growth and development, in addition to the supply of water and nutrients, it is also regulated by some physiologically active substances. These substances that regulate and control plant growth and development are called plant growth substances. Plant growth substances include two types: one is produced in the process of plant metabolism, which is called phytohormone. Second, synthetic organic substances with phytohormone activity are called plant growth regulators.
I. Plant hormones
Plant hormones have four important characteristics: endogenous, which is the product of cells in plant life activities and widely exists in the plant kingdom. Regulation can regulate the growth and development of plants through their own life activities. Mobility, which can be transported from the synthetic site of plants to the functional site. Significantly, the content in plants is very small, mostly calculated in micrograms, but it can play an obvious synergistic role. There are five internationally recognized plant hormones: auxin, gibberellin, cytokinin, abscisic acid and ethylene.
1. Plant hormones
Characteristics of auxin: auxin is indoleacetic acid, referred to as IAA (figure 12- 1). Because auxin is easily destroyed in plants, plants are generally not treated with indoleacetic acid, but with similar growth regulators such as indolebutyric acid and naphthylacetic acid.
The role of auxin: promoting the elongation and growth of plants, promoting the rooting of cuttings, inducing parthenocarpy, and controlling male and female sex. The most basic physiological function of auxin is to promote growth, but it is related to the concentration of auxin, plant species, age of organs and cells. Low concentration of auxin can promote growth, while high concentration of auxin can inhibit growth. Dicotyledons are usually more sensitive than monocotyledons. Roots are more sensitive than buds, buds are more sensitive than stems, and young cells are more sensitive than mature cells.
2. Gibberellin
Characteristics of gibberellin: Gibberellin is called GA for short (Figure 12-2). The prepared solution is easy to fail, and it is suitable to be stored in powder form under the condition of low temperature drying.
Physiological functions of gibberellin: promoting the growth of stems and leaves, inducing bolting and flowering, promoting gender differentiation, breaking dormancy, preventing shedding, inducing parthenocarpy and promoting the formation of seedless fruits.
3. Cytokinin
Characteristics of cytokinin: Cytokinin is abbreviated as CTK (Figure 12-3). It mainly includes kinetin, zeatin and so on. The nature is relatively stable.
Physiological functions of cytokinin: promoting cell expansion and growth, inducing bud differentiation, preventing aging and promoting axillary bud growth.
4. abscisic acid
Characteristics of abscisic acid: ABA for short (figure 12-4). It is a powerful natural inhibitor existing in plants, with minimal content, high activity and great effect.
Physiological functions of abscisic acid: inhibiting plant growth, promoting abscission, promoting dormancy and regulating stomatal closure.
5. Ethylene
Characteristics of ethylene: ethylene is abbreviated as ETH (Figure 12-5). It is a gaseous hormone that promotes the maturation of tissues and organs. Because ethylene is a gas, it is difficult to use, so it is generally replaced by its analog ethephon.
Physiological functions of ethylene: accelerating fruit ripening, promoting abscission and senescence, regulating plant growth and promoting flowering.
In the process of plant growth and development, any physiological reaction is not the result of a single hormone, but the result of the interaction of multiple hormones. The interaction between various hormones is very complicated, sometimes it is synergistic and sometimes it is antagonistic. It is of great significance in agricultural production to understand the physiological effects of various hormones on plants, the interaction between hormones and the relationship with the environment.
Second, plant growth regulators.
With the research and development of plant hormones, in order to control the growth and development of plants more effectively, many substances with hormone activity have been synthesized, which are widely used plant growth regulators at present.
1. growth promoter
Naphthylacetic acid (NAA): Cutting rooting, controlling branch growth, thinning flowers and fruits, preventing fruit drop before harvest and promoting pineapple flowering, is widely used for rooting in tissue culture (Figure 12-6).
Indobutyric acid (IBA): It is mainly used to promote the rooting of cuttings on fruit trees and produce many slender adventitious roots. It is used for rooting in tissue culture. Indoleacetic acid is the most important regulator at present because of its wide adaptability and high safety (figure 12-7).
2,4-Dichlorophenoxyacetic acid (2,4-d): It can be used as herbicide at high concentration, prevent tomato from falling flowers and fruits and induce seedless fruit formation at low concentration, and induce explant dedifferentiation at appropriate concentration in tissue culture (Figure 12-8).
Naphthoxyacetic acid (NOA): Promote cuttings to take root and prevent fruits from falling off before harvest (Figure 12-9).
6- benzyl adenine (6-BA, BAP): scientific name: Green Dan. It can significantly increase the fixation of grape fruit grains and fruit stalks, reduce the abscission of fruit grains, promote the germination of apple lateral buds and increase the branching angle, which is widely used in tissue culture (figure 12- 10).
Dihydrozeatin: promotes cell division and plant growth (Figure 12- 1 1).
2. Growth promoters and growth inhibitors
Ethephon (CEPA): Ethephon is the most widely used regulator in production at present, and its optimum temperature is 20℃-30℃. Promoting fruit ripening, inhibiting vegetative growth, promoting flower bud formation, inducing female flower formation and male flower sterility, promoting rubber milk secretion, delaying flowering, early dormancy and improving cold resistance (figure 12- 12).
Chlormequat chloride (CCC): inhibits vegetative growth, makes the stems of plants thicker, leaves darker, leaves thicker and wider, can better carry out photosynthesis, resist lodging, promote flower bud formation, and increase fruit setting rate (Figure 12- 13).
Triiodobenzoic acid (TIBA): A substance that hinders the transport of auxin. Eliminate apical dominance, promote axillary bud growth, increase branches and dwarf plants (figure 12- 14).
Bijiu (B9): Inhibit the apical dominance, stimulate the growth of new shoots of fruit trees, promote the formation of flower buds, reduce the fruit drop before harvest and promote the fruit coloring. Bijiu is widely used in agricultural production, but some experiments show that Bijiu has toxic and side effects on people and livestock, and is highly carcinogenic, so it should be banned in agricultural production (Figure 12- 15).
Paclobutrazol (PP333): delaying vegetative growth and promoting reproductive growth (figure 12- 16).
Maleic hydrazide (MH fresh element): inhibit the elongation of stems and prevent onions, potatoes, garlic, etc. Germinate during storage, and inhibit the growth of tobacco axillary buds (figure 12- 17). However, maleic hydrazide may cause cancer and distort animal chromosomes, so it is best not to use it for edible plants.
Morphogen: It can inhibit the elongation of stems and seed germination, and promote the seedless fruits of grapes, tomatoes and other crops (Figure 12- 18).
Uniconazole (S3307): Its physiological function is the same as that of paclobutrazol, but it is 2-4 times stronger than paclobutrazol. It is a widely used plant growth regulator at present (figure 12- 19).
Plant hormones and plant growth regulators are widely used in agricultural production. For the convenience of use, their functions and applications are listed in the attached table for your reference.