The differences between plant hormone and plant growth regulator
Plant growth substances include two broad categories: the first one is generated in the metabolic processes of plants, which can be called the plant hormone. The second one is called the growth regulator which is a kind of organic matter artificially synthesized and has the plant hormone activity.
Plant hormone has four kinds of important characteristics: endogenous, it is the product inside the cells in the plant life activity and is widely existed in the plant kingdom. Regulatory, it can control plant growing development by adjusting their life activities. Mobility, it can transport from the synthetic site to acting site in the plant. Remarkable results, although it has little content in the plant body and mostly calculated with micrograms, it can play an obviously synergistic effect. There are five broad categories of internationally recognized plant hormones which are auxin, gibberellin, cytokinin, abscisic acid and ethylene.
The speciality of auxin: auxin is the same with indole-acetic acid which can be called IAA for short. As auxin can be easily destroyed in the plant body, we mostly use the growth regulators similar to indole-acetic acid such as the indolebutyric acid and naphthalene acetic acid in treatment of plant in the production instead of indole-acetic acid.
The effect of auxin: it can promote the plant elongation growth, promote the cuttings rooting, induce the parthenocarpy and control male and female gender. The most basic physiological effect of auxin is reflected in promoting growth which also has relations with the auxin concentration, plants types, organs and cells age and other factors. For example, it will promote the plants growth under low auxin concentration and will inhibit the plants growth under high auxin concentration. Dicotyledons are more sensitive than monocotyledons. Root is more sensitive than bud, bud is more sensitive than stem and the young cells are more sensitive than mature cells.
The speciality of gibberellins: it can be called GAA for short. As it can easily lose its effect in the form of solution, it should be stored in the form of powders under low temperature and dry conditions.
Physiological effects of gibberellins: it can promote the growth of stem and leaf, induce the bolting flowering, accelerate sex differentiation, break dormancy, prevent fruit drop, induce parthenocarpy and promote the formation of stenospermocarpy.
The speciality of cytokinin: it can be called CTK for short which mainly includes kinetin, zeatin, and so on. It also has stable characteristic.
Physiological effects of cytokinin: it can promote cell expansion growth, induce buds differentiation, prevent aging and promote axillary bud growth.
The speciality of abscisic acid: abscisic acid can be called ABA for short which is a strong natural inhibitor in the plant and has minimal content, very high activity and huge effect.
Physiological effects of abscisic acid: it can inhibit the plant growth, promote the fruit drop and dormancy and adjust stomatal closure.
The speciality of ethylene: it can be called ETH for short which is a kind of gaseous hormone in promoting the tissues and organs mature. As ethylene is gas and is difficult to use, it is often replaced by its analogue of ethephon.
Physiological effects of ethylene: it can accelerate fruit maturation, promote the fruit drop and aging, adjust the plant growth and promote flowering.
In the process of plant growth and development, any kind of physiological reaction is not the result of single hormone function, but the result of various hormones interaction which is very complex, sometimes reflected in the synergism and sometimes reflected in antagonism. Understanding the physiological effect of various homones on plant, the interactions between the homones and the relationship with environment will have very important significance in agricultural production.
Plant growth regulator
With the research and development of plant hormones, people compound many substances that have hormonal activity so as to effectively control the plant growth, which is the currently widely used plant growth regulator.
Naphthalene acetic acid (NAA): it is used in cutting and rooting, controlling branch growth, blossom and fruit thinning, preventing preharvest fruit drop, promoting pineapple flowering and widely used in taking root in the tissue culture.
Indolebutyric acid (IBA): it is mainly used in promoting the cutting and rooting of fruit trees, which will lead to numerous and tenuous adventitious root. It is also can be used in taking root in the tissue culture. Due to its wide applicable range and safety, it has become the leading modifier at present.
24-dichlorophenoxyacetic acid (24-D): it can be used as weed killer with high concentration and can prevent the blossom and fruit drop of tomatoes and induce the formation of seedless fruits with its low concentration. Besides, it can induce explants dedifferentiation with appropriate concentration in the tissue culture.
Naphthoxyacetic acid (NOA): it can be used in cutting and rooting and preventing preharvest fruit drop.
6-Benzylaminopurine (6-BA, BAP): its scientific name is verdan. It can obviously enhance the fitness of grape fruit and carpopodium and reduce the fruit drop. It can also promote apple lateral bud germination and increase the branching angle. It is widely used in the tissue culture.
Dihydrozeatin: it can promote cell division and promote plant growth.
Growth continued agent and growth inhibitor
Ethephon (CEPA): it is the most widely used modifier in the production. With the optimal temperature of 20-30 degrees Celsius, it will begin to take effect. It can promote fruit mature, inhibit the nutrition growth, promote the flower bud formation, induce female flower formation and male infertility, promote rubber milk secretion, delay flowering period, early dormancy and improve cold resistance.
Chlormequat chloride (CCC): it can inhibit vegetative growth, bold plant stems, deepen leaf color, thicken and widen blade, thus the plant will be able to carry out photosynthesis better. It also can be resistant to lodging, promote the flower bud formation and increase fruit-set.
Triiodobenzoic acid (TIBA): it is a kind of substance that can hinder the auxin transportation. It can eliminate the apical dominance, promote the growth of axillary buds, increase the branch and dwarf the plants.
Daminozide (B9): it can inhibit the apical dominance, stimulate new shoot growth of fruit trees, facilitate the flower bud formation, reduce preharvest fruit drop and promote fruit coloring. Although it has relatively wide application on the agricultural production, it should be prohibited to use in the agricultural production as it has toxic and side effect on humans and will have intense carcinogenicity.
Paclobutrazol (PP333): it can delay the plant vegetative growth and promote reproductive growth.
Maleic hydrazide (MH maleic hydrazide): it can inhibit stem elongation, prevent the sprout of onions, potatoes and garlic in their duration storage and inhibit the growth of tobacco axillary bud. However, it may cause cancer and animal chromosomal aberrations. Therefore, it should not be used in the edible plants.
Chlorflurenol-methy (morphactin): inhibit the stem growth and elongation, suppress the seed germination and promote the seedless fruit of grapes, tomatoes and other crops.
Uniconazole (S3307): it is a kind of plant growth regulator widely used at present that has same physiological effects with paclobutrazol and 2-4 times stronger than paclobutrazol.