The relationship between plant hormones
Regulation of plant growth is influenced by a variety of growth substances. It worked by several hormones more often than a single hormone. There is a balance between them, which has both mutually reinforcing effects, but also the role of mutual antagonism.
Auxin and gibberellic acid
Low concentrations of auxin and gibberellic acid have the growth-promoting effect on isolated organ, such as coleoptiles, hypocotyls and stem. The effects of Auxin are not significantly than gibberellic acid when used alone, but when combined with the effect of promoting growth is better than alone, this shows that auxin and gibberellic acid have mutually reinforcing additive effect.
Auxin and Cytokinin
Cytokinin enhanced polar auxin transport, which can enhance the physiological effects of auxin. Nevertheless, they are mutually antagonistic in the interaction of top buds and lateral buds. For example, auxins can promote growth of apical buds and the maintenance of apical dominance. Cytokinins promote lateral buds growth breaks apical dominance.
Furthermore, these two hormones also control callus roots and buds. Stem Center of tobacco callus culture experiments have shown that if the ratio of CTK/IAA is high, the callus on differentiation budding; when CTK/IAA ratio is low, it is conducive to the differentiation of roots; when the ratio is in the middle level, callus only growth without differentiation. This effect has been widely utilized in tissue culture.
Auxin and ethylene
a. Auxins promote ethylene biosynthesis
In the process of promoting pineapple flowering and cucumber female flower differentiation, auxin and ethylene have the same physiological effects. What is the relationship between them? It turned out that it is the role of ethylene in the above process. Auxins promote ethylene biosynthesis, and while auxin concentration is significantly higher, the more production of ethylene. Therefore, high concentrations of Auxin inhibit growth.
b. The inhibitory effect of ethylene on Auxin
The effects of auxin on ethylene present in three aspects: inhibition of polar transport of IAA and biosynthesis of auxin and the promotion of the activity of IAA oxidase. In short, auxin content decreased under the action of ethylene. Therefore, ethylene has the inhibitory effect on the growth.
GA and ABA
In the relationships of germination and dormancy, the roles of GA and ABA are opposite: GA can break dormancy, and ABA is able to inhibit the germination and promote sleep. It is worth noting that, in the GA and ABA biosynthesis, two hormones have common precursor substances, and some of the intermediate steps are the same. But the environmental conditions affect both the synthesis, thereby affecting the growth of plants. When in long-day conditions, it will synthesize GA, and promote growth; under short-day conditions, it will synthesize abscisic acid, and promote sleep.
Cytokinins and Abscisic acid
Abscisic acid strongly inhibits growth and accelerates the aging process, but this might be changed by cytokinin. Cytokinin inhibited the degradation of chlorophyll, nucleic acid and protein, thereby inhibiting leaf from senescence. But ABA inhibited the synthesis of nucleic acids and proteins, increasing the activity of nucleic acids so as to accelerate leaf senescence. They can also adjust the opening and closing of stomata with ABA promoting the closing while cytokinins promoting the opening.