Brassinolide, a growth‐promoting steroidal lactone

We have studied the effect of brassinolide (BR), a plant steroidal lactone, on the expression of auxin-regulated genes in soybean (Glycine max L. cv Williams 82) epicotyls. BR caused up to 4-fold increases in epicotyl length during extended assays at 10-M, in the absence of added auxin. Structurally related steroids failed to induce elongation or to alter the BR effect. Northern blot analysis, using sequences corresponding to auxin-regulated genes as probes, has shown that the molecular mechanism of BR-induced elongation is likely to differ from that of auxin-induced elongation in this system. BR does not rapidly induce members of the GH, SAUR, or ICW auxin-inducible gene families before the onset of elongation. BR enhances SAUR and GH1 transcripts after 18 h but has no effect on JCW1 or GH3 transcripts at any time examined. We have shown by two-dimensional gel analysis of in vitro translated mRNA that a submicromolar concentration of BR alters the pattern of gene expression in elongating soybean epicotyls.BR2, a plant growth-promoting steroidal lactone, is the most biologically active compound of a group of related natural products termed brassinosteroids (reviewed in ref. 13). BR elicits a broad spectrum of responses in plants including enhanced cell elongation (13) and division and differentiation (6), and a strong case recently has been made for brassinosteroids as a sixth class of endogenous plant growth regulators (25). Like auxin, BR has pronounced effects on the elongation of stem tissue. Maize mesocotyls, pea, Azuki bean, and mung bean epicotyls (9, 13, 30), bean and cucumber hypocotyls (12,14), and wheat coleoptiles (23) all respond to submicromolar concentrations of BR by elongating. It has been suggested that the effects of BR are mediated through auxin or that BR increases tissue sensitivity to endogenous auxins (13). Despite numerous physiological studies addressing BR-auxin interactions, there have been few studies reported in which molecular techniques were utilized to clarify the interaction of these growth regulators (6). '

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confidence: 99%

Effect of Brassinolide on Gene Expression in Elongating Soybean Epicotyls

Clouse

Zurek²,

McMorris³

et al. 1992

“…(13) and needles of spruce (14). Because IAA appears to play an important role in the regulation of cambial activity in woody plants (6), and BR is known to interact synergistically with IAA (1,3,8,10,16,17), we looked for BRs in scrapings ofthe cambial region of Scots pine (Pinus silvestris) harvested during the cambial growing period. In the process, we also developed a sensitive and simple dwarfrice lamina inclination bioassay based on the intact seedling assay of Takeno and Pharis (10).…”

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confidence: 99%

Identification of Two Brassinosteroids from the Cambial Region of Scots Pine (Pinus silverstris) by Gas Chromatography-Mass Spectrometry, after Detection Using a Dwarf Rice Lamina Inclination Bioassay

Kim¹,

H²,

Little³

et al. 1990

A simple and improved dwarf rice (Oryza sativa var Tan-ginbozu) lamina inclination bioassay for brassinosteroids (BRs) was developed based on a previously published method (K Takeno, RP Pharis [1982] Plant Cell Physiol 23: 1275-1281). The assay used 3-day-old intact seedlings, and detection of BR was made more sensitive by synergizing the response to BR with indole-3-acetic acid (IAA). The minimum detectable amount of BR was less than 0.1 nanogram/rice plant (brassinolide equivalents). Purification steps for isolation of BR from tissue scrapings taken from the cambial region of Scots pine (Pinus silverstris) harvested during the period of rapid wood production were guided by this assay. After column chromatography (silica gel and PrepPak C18) and reversed phase Cie high performance liquid chromatography, the biologically active fractions were analyzed by gas chromatography-mass spectrometry (GC-MS) and/or GC-MS-selected ion monitoring. Two BRs, castasterone (major) and brassinolide (minor) were identified. This is the first identification of BR from the cambial region of a conifer.Brassinosteroids (BRs)4 are steroidal hormones that promote plant growth. To date, 28 naturally occurring BRs have been identified in various plant tissues (2,4,5,8,16), ranging from higher plants to a green alga ( 15). In conifers, castasterone (scheme 1, structure 2) and typhasterol (2-deoxycastasterone (scheme 1, structure 3) have been identified in pine pollen

“…It also means that the membrane potential reflects proton pumping more sensitively than medium acidification does, thereby allowing a discrimination with respect to the potency of the substances (no unambiguous effect of stigmasterol on the membrane potential in the light, in the dark occasionally hyperpolarization of transient character). These results suggest the existence ofa mechanism ofaction brought about by steroids on proton pumping that varies from that of IAA (15) and FC, respectively. The reasons for this are: (a) in contrast to FC, the effect of the steroids on the membrane potential and on medium acidification is reversible; and (b) SSHB significantly stimulated FeCN reduction also in the light.…”

Section: Discussionmentioning

confidence: 76%

“…Egeria leaves (10)(11)(12)(13)(14)(15) were incubated for 1 h in 2 mL of a solution containing 4 nm (reference 500 nm). The experiments were peformed at least three times with five replicates.…”

Section: Reduction Of Fecnmentioning

confidence: 99%

Effects of (22S,23S)-Homobrassinolide and Related Compounds on Membrane Potential and Transport of Egeria Leaf Cells

Dahse¹,

Sack²,

Bernstein³

et al. 1990

ABSTRACT(22S,23S)-Homobrassinolide was tested for its effect on the electric cell potential, proton extrusion, ferricyanide reduction, and amino acid and sucrose uptake of leaves of Egeria densa Planchon. In the light, (22S,23S)-homobrassinolide and its derivative, 2a-3a-dihydroxy-5a-stigmast-22-en-6-one, were similar to each other and similar to fusicoccin in causing hyperpolarization and proton extrusion, whereas stigmasterol was less effective. In darkness, the three sterols showed comparable effects.(22S,23S)-Homobrassinolide slightly stimulated ferricyanide reduction and promoted uptake of sucrose and a-aminoisobutyric acid. The results are compatible with a stimulation of an electrogenic proton pump mechanism at the plasmalemma by (22S,23S)-homobrassinolide.behavior to auxin in corn roots (14) suggests an FC3-like mechanism of action for this compound. Unfortunately, the structural requirements of the steroid backbone, responsible for the stimulation of transport by brassinosteroids, is not yet clear, although some work was dedicated to this issue (10). In order to characterize further the role of the steroid structure in modifying transport on the cellular level, we here describe the effects of another potent synthetic analog, SSHB (1 in Fig. 1), on the membrane potential and on proton and solute transport of Egeria densa, a submerged aquatic weed well characterized in this respect (5, 6, 12), and we compare the SSHB effect with those induced by related substances and FC. MATERIALS AND METHODS Plant CultivationBrassinosteroids are a new class of growth regulators found in many plants (1, 10). Among them brassinolide, (22R,23R,24S)-2a,3a,22,23-tetrahydroxy-24-methyl-Bhomo-7-oxa-5a-cholestan-6-one, is the best characterized and causes the highest growth promotion. The comparison with other plant hormones in a series of bioassays revealed auxinlike properties, albeit a powerful synergism between brassinolide and IAA was reported (1 1, 15