Gibberellin contains (-)-gibberellin skeleton, which is a diterpene compound with complex chemical structure. The closest precursor of gibberellin in higher plants is usually considered to be kaurene. Different gibberellins differ in the number and position of double bonds and hydroxyl groups. Free gibberellin is a mono-,di-or tri-carboxylic acid with 19c or 20c. Most of the bound gibberellins are glucosinolates or glucoesters, which are easily soluble in water.
Gibberellin can be extracted with methanol. Different gibberellins can be separated by various chromatographic analysis techniques. The purified gibberellin was diluted and treated with dwarf plants such as dwarf corn, and its biological activity could be identified by observing its effect of promoting high growth. Different gibberellins have different biological activities, and gibberellic acid (GA3) has the highest activity. Compounds with high activity must have a gibberellin ring system (cyclic ABCD), with carboxyl groups on C-7 and lactone rings on A ring.
The content of gibberellin in different parts of plants is different, and it is the most abundant in seeds, especially at maturity.
1. Distribution: It is widely distributed in angiosperms, gymnosperms, ferns, brown algae, green algae, fungi and bacteria, and mostly exists in vigorous growth parts, such as stem tips, tender leaves, root tips, fruit seeds and so on. Content:1~100 ong g-1fresh weight. The gibberellin content of fruits and seeds (especially immature seeds) is two orders of magnitude higher than that of vegetative organs. Every organ or tissue contains more than two kinds of gibberellins, and the species, quantity and state (free or bound) of gibberellins change with the development period of plants.
2. Transportation-GA is different from auxin, and its transportation does not show polarity. (Root tip synthesis-transported upward along the catheter, young leaves generated-transported downward along the sieve tube). The transportation speed of different plants is quite different, such as 5 cm h- 1 for dwarf pea, 2. 1 for pea and 0.42 mm h- 1 for potato.
3. Form of existence: free gibberellin)-does not bind with other substances in the form of bonds, and is easily extracted by organic solvents. Belonging to physiological activities; Conjugated gibberellin)-Gibberellin combines with other substances (such as glucose), and only through acid hydrolysis or protease decomposition can free gibberellin be released, which is physiologically inactive. Binding type: This is a storage form of GA. When seeds mature, GA is transformed into bound storage, and when seeds germinate, GA is transformed into free storage, which plays its regulatory role.
4. Main dosage forms and contents: 4% Gibberellic acid emulsifiable concentrate, 6% gibberellin aqueous solution, 40% Gibberellic acid granules, 20% soluble tablets, 75% crystalline powder and 85% crystalline powder. The main manufacturers are: Qingdao Lily Source Bioengineering Co., Ltd., Zhejiang Qianjiang Biochemistry Co., Ltd. and Shanghai Tongrui Biotechnology Co., Ltd.
The most prominent physiological function of gibberellin is to promote stem elongation and induce short-day bolting and flowering of long-day plants. Different plants are sensitive to gibberellin. Genetic dwarf plants, such as dwarf corn and pea, are most sensitive to gibberellin, and the plant type after gibberellin treatment is similar to that of non-dwarf plants. Non-dwarf plants have only a slight reaction. Some plants are genetically short because they lack endogenous gibberellin (others are not). Gibberellin plays a regulatory role in seed germination. Starch in the seeds of many cereal plants, such as barley, is rapidly hydrolyzed during germination; If the embryo is removed, the starch will not hydrolyze. When gibberellin is used to treat non-embryonic seeds, starch can be hydrolyzed again, which proves that gibberellin can replace embryos to cause starch hydrolysis. Gibberellin can replace red light to promote the germination of lettuce seeds, and replace the vernalization of carrots. Gibberellin can also cause parthenocarpy in some plants. For some plants, especially seedless grape varieties, gibberellin treatment at flowering stage can promote the development of seedless fruits. But sometimes it can also inhibit some physiological phenomena.
Regarding the mechanism of gibberellin, the starch hydrolysis induced by gibberellin in degerminated barley seeds was deeply studied. The sterilized degerminated barley seeds were treated with gibberellin. It was found that GA3 significantly promoted the new synthesis of aleurone layer α -amylase and caused starch hydrolysis. When the whole barley seed germinates, the embryo contains gibberellin, which is secreted to aleurone layer. In addition, GA3 also stimulated aleurone layer cells to synthesize protease and promoted the secretion of ribonuclease and glucanase.
The application of gibberellin in agricultural production has good results in some aspects. For example, increase the yield of seedless grapes and break the dormancy of potatoes; When brewing beer, GA3 was used to promote the germination of barley seeds to prepare maltose. When heading of late rice is slow due to rainy weather and low temperature, gibberellin treatment can promote heading; Or adjust the flowering period in hybrid rice seed production to make parents meet at this flowering period.
If excessive gibberellin is used, the side effect will cause lodging, so it is necessary to use growth-promoting hormone to adjust and increase potassium fertilizer.
A plant hormone with tetracyclic diterpenoids as the basic skeleton of trans-erythromelamine. Biosynthesis by ent- ka-urene. According to the sequence of separation, it was named gibberellin A (abbreviated as GA). More than forty kinds of gibberellins have been identified, but not all of them have physiological functions. C 19-GA exists in the form of bound gibberellin with r- lactone and its precursor C20-GA. GA was isolated from the culture solution of rice bakanae fungus [the complete generation was GI-B Berella Fujikuroi (Sawada) W λ, and the incomplete generation was Fusarium moniliforme. Sheldon was discovered by Hideki Kurosawa in 1926, and later by Kenichiro Toshida and Yukuke Sumi (650). The effective components of this crystal were later identified as the mixture of GA 1, GA2 and GA3. Since J. MacMilan and J. Suter (1958) isolated GA 1 from higher plants, more than 20 lower plants containing gibberellin have been obtained so far, and they also exist widely in the plant kingdom. In higher plants, gibberellin is synthesized in immature seeds, terminal buds and roots. The typical physiological function of GA is to promote the growth of branches, especially the overall growth of harmless plants. Dwarfing of plants is considered to be mainly caused by genetic abnormality of GA synthesis system in vivo. In order to supply GA, dwarfing can return to normal. Even under the condition of no induction, GA treatment can make plants bolting in rosette shape. Generally, it has no effect on the growth of roots. The role of GA in promoting growth is considered to be promoting cell division and cell elongation, but it is considered that the role of GA in promoting cell elongation is closely related to the role of auxin. In addition, GA can break the dormancy of seeds and buds, promote short-day flowering of long-day plants, induce parthenocarpy of grapes, and inhibit leaf senescence of some plants. In aleurone layer of cereal seeds, it can induce the re-synthesis of hydrolases such as α -amylase (endosperm assay), ribonuclease and protease.
Gibberellin is a plant hormone belonging to diterpenoids. During 1926, Japanese pathologist Akira Kurosawa found that the overgrowth of rice plants was caused by the secretion of Gibberella. 1935 An active product was isolated from Gibberella in Putian, Japan, and was named gibberellin (GA) after crystallization. Gibberellin was first isolated and identified as gibberellic acid (GA3), and more than 70 gibberellins have been isolated from higher plants and microorganisms. Gibberellin is acidic because it contains carboxyl groups. Endogenous gibberellin exists in free and combined forms and can be transformed into each other.
Gibberellin is the most stable solution with a pH of 3~4. Too high or too low pH will make gibberellin become pseudogibberellin or gibberellic acid with no physiological activity. The precursor of gibberellin is kaurene. Some growth retardants such as Amo-16 18 and chlormequat can inhibit the formation of kaurene, while Fosfon -D can inhibit the transformation of kaurene into gibberellin. Gibberellin is usually formed in tender leaves, buds, young roots and immature seeds of plants. Different gibberellins exist in different organs of various plants. Gibberellin formed at the top of young leaves and shoots is exported through phloem, and gibberellin produced at the root is transported upward through xylem.
Among gibberellins, GA3 has the strongest physiological activity, and it is also the most studied one. It can significantly promote the growth of plant stems and leaves, especially for genetically and physiologically dwarfed plants. It can replace the light and low temperature conditions needed for germination of some seeds, thus promoting germination; It can make long-day plants bloom under short-day conditions and shorten their life cycle; It can induce flowering, increase the number of male flowers in melons, induce parthenocarpy, improve fruit setting rate, promote fruit growth and delay fruit senescence. In addition, GA3 can also be used to prevent pericarp rot. Spraying cotton at full flowering stage can reduce the shedding of buds and bolls; Soaking potato seeds can break dormancy; Soaking barley seeds can increase maltose production and so on.
Many physiological effects of gibberellin are related to its regulation of nucleic acid and protein in plant tissues. It can not only activate various hydrolases in seeds, but also promote the synthesis of new enzymes. The most studied is the significant effect of GA3 on the production of α -amylase in barley grains. In addition, it also induces the synthesis of protease, β- 1, 3- glucosidase and ribonuclease. Gibberellin stimulates stem elongation, which is related to nucleic acid metabolism. It first acts on deoxyribonucleic acid (DNA) to activate DNA, then transcribes it into messenger ribonucleic acid (mRNA), and then translates it from messenger ribonucleic acid into specific protein.
Physiological function of gibberellin
Promoting the transformation of maltose (inducing the formation of α -amylase); Promote vegetative growth (not promoting the growth of roots, but significantly promoting the growth of stems and leaves), prevent organ loss, and break dormancy.
Gibberellin's most prominent function is to accelerate cell elongation (gibberellin can increase the content of auxin in plants, which directly regulates cell elongation), and it can also promote cell division and cell expansion (but it will not cause cell wall acidification).