Brassinolides hormones

In 1979, a novel plant growth regulating steroidal substance called brassinolide was isolated from rape (Brassica napus) pollen. Brassinosteroids are thought by some to be a new class of plant hormones. The evidences are ... 

The use of Z-ray diffraction to assign structures to unusual steroid derivatives has been briefly reviewed.3 It includes reference to brassinolide (3), a steroidal plant growth hormone. Another unusual product assigned its structure by the X-ray method is the spiro-lactone (4), derived by thallium triacetate oxidation of 5a-cholestane-3,4-dione.4... 

J.H. Yopp, Southern Illinois University, Carbondale, became interested in the brassins project in its early stages (36) and he conducted cooperative brassins studies with both Mitchell and Mandava. Yopp et al. (37, 38) evaluated brassins responses in a number of auxin, gibberellin, and cytokinin bioassays and showed that brassins responded similarly to some of the known hormones in certain systems but not in others. These studies led to more cooperative investigation of brassinolide and other brassinosteroids (39, 40). 

Generally, immature seeds have been demonstrated to be one of the richest sources of plant hormones. Thus, Yokota et al. examined brassinosteroids in immature seeds ofDolichos lablab (12-15). As a result, two brassinosteroids with a 24-exomethylene [ dolicholide (2) and dolichosterone (4) ] two Cs brassinosteroids with a 24(E>ethylidene [ homodolicholide (10) and homodolichosterone (11) ] and two 6-deoxodihydro brassinosteroids [ 6-deoxodihydrocastasterone (5) and 6-deoxodihydrodolichosterone (6) ] were unequivocally identified and later the presence of brassinolide and castasterone were determined. The content of the major brassinosteroid, dolicholide, was 200 ig/kg, which paralleled the concentration of brassinolide in rape pollens. 

The identification of brassinolide (1) by workers at the USDA laboratories in Beltsville, Maryland in 1979 (1) was a most significant event because it established steroids as a new class of plant hormones. We were particularly interested in the structure of brassinolide as a result of our studies with somewhat... 

Specificity. Using the first member of the family, brassinolide (BR), an extensive survey of its effects in 17 bioassays, which varied in their responses to gibberellins, auxins and cytokinins, showed that BR did not behave exclusively as any one of those hormones. In some supposedly specific bioassays BR was as effective, or more so, as the hormone the assay was supposed to detect (9,10). This also applies to the rice lamina inclination assay (11), which is now frequently used. 

Thus it is no longer possible to assume standard bioassays are specific, and brassinolide cannot be classified as belonging to any of the known groups of plant hormones. Indeed, one reviewer has remarked ". . it could be considered to belong to all of them " (12). The "brassin response" of swelling and splitting in... 

We conclude that the conditioning seems to be a very complex and not yet well known phenomenon in which hormones, such as brassinolide, may have a synergistic effect with conditioning factors. 

In wheat, the ear weights of both tillers and the main stem were increased, in comparison with untreated controls by brassinolide (BR) sprays (I). In corn, BR treatment had significant influence on the length of the unfertile tip portion of the ear and on the number of vacant kernels. The yield increased compared with untreated controls (2). Little is known of the effect of BR on the ripening of rice plants, and the mode of action of BR on the ripening of rice has not been studied. To increase crop yield, it is necessary to improve the photosynthetic efficiency and promote the translocation of photosynthetic products in the panicles. Therefore, we assessed the ripening of rice, the translocation of photosynthetic products, and plant hormone levels in panicles. 

Flowers of Morita navel oranges were treated with brassinolide solution at anthesis. Fruit set of trees treated with 0.1 and 0.01 ppm brassinolide increased by ca. 5 and 2.5 times respectively, when surveyed 50 days after treatment. At harvest there were no differences in quality between treated and untreated fruits. Since brassinolide-treated squash segments only showed slight changes in hormone content, brassinolide may have a direct action on stimulating fruit set without marked changes in the levels of other endogenous phytohormones. 

Historical Background. This chapter summarizes the USDA s contributions to brassinolide research, a field that has attracted very much attention since the discovery of brassinolide from rape pollen in 1979. For several decades, plant scientists have been investigating the reproductive process in plants, but without much success. In vertebrates, it is known that sex hormones are involved in the reproductive process. Such a process is poorly understood in plants. In the late 1930s, USDA scientists initiated pollen research to gain some insight into the plant reproductive system. We consider this initiative to be the beginning of brassinolide research. 

Discovery of Brassinolide. Being thoroughly convinced that the pollen growth factors were different from the known hormones, Mitchell collaborated with Bhushan Mandava to determine the factors responsible for biological activity. 

Until the discovery of brassinolide by USDA scientists in 1979, it was thought that only five groups (indole auxins, gibberellins, cytokinins, abscisic acid, and ethylene) of hormones were responsible for regulating plant growth and development. Following this discovery, a number of compounds similar to brassinolide both in structure and physiological activity were isolated from different parts of plants. On the basis of published... 

Hormonal properties on plants. The occurrence and distribution of the brassinosteroids in assorted plant tissues has been comprehensively discussed (2). They occur in immature seeds, leaves, stems, shoots, pollen, and fruit. Furthermore, they have been found in insect galls and the corresponding healthy tissues. Although the chemical species remained the same in both sets, only brassinolide occurred in galls, but not in healthy tissues. Again, these compounds... 

There is further evidence to support the claim that brassinosteroids are hormonal in their action (6). These are the effects of brassinolide on gravitropism (7), effects in conjunction with light quality (8), effects on photosynthate partitioning (9), probable effects on phytochrome (10), substitution for indole-3-acetic acid in soybean epicotyls (11), enhancement of xylem differentiation (11), stimulation of membrane permeability in cucumber hypocotyls (12), and stimulation of ATPase activity (12). Taken objectively, many of these specific physiological and biochemical functions which are attributed to brassinolide, and by inference to the brassinosteroids in general, have been attributed to the other plant hormones, especially indole-3-acetic acid and the gibberellins (6, 13). 

The results of the rice lamina inclination test (RLIT) indicated an extraordinary high activity of 25-hydroxy-24-epibrassinolide (90). This compound is about ten times more active than 24-epibrassinolide (12), indicating that the hydroxylation at C-25 is an activating step in the brassinosteroid metabolism. Therefore, 25-hydroxy-24-epibrassinolide (90) is, next to brassinolide (1), one of the most active brassinosteroids known until now. In comparison with 25-hydroxy-24-epibrassinolide (90), the 26-hydroxylated metabolite (91) was clearly less active. As in other groups of steroidal hormones, for instance vitamine D metabolites, hydroxylation at C-25 seems to be essential for high activity. ... 

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