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At least 343 records · Page 19Linked to original sources
PubMed2005

Phloem and xylem specification: pieces of the puzzle emerge.

The plant vascular system is composed of two tissue types, xylem and phloem, which originate from the vascular meristem, the procambium. Recently, several regulatory mechanisms that control the specification of these two tissue types have been uncovered. These include the asymmetric patterning of xylem and phloem in the vascular bundle by the class III HD-ZIP and KANADI genes, the tissue-type-specific control of vascular cell proliferation by brassinosteroids and class III HD-ZIP genes, the regulation of vascular tissue identity by the MYB-like transcription factor APL, and inductive signalling during xylem differentiation by xylogen. These findings define an emerging developmental framework for the control of vascular tissue specification.

Body Patterning↗
PubMed2005

Sending the right signals: regulating receptor kinase activity.

Knowledge of the functions of plant receptor-like-kinases (RLKs) is increasing rapidly, but how their cytoplasmic signalling activity is regulated and how signals are transduced to cytoplasmic or nuclear proteins remain important questions. Recent studies, particularly of the BRASSINOSTEROID INSENSITIVE1 RLK, have begun to shed light on the mechanistic details of RLK activation, including the possible role of ligand binding. Studies of this and other RLKs have also highlighted the potential importance of hetero-oligomerisation and receptor internalisation in RLK signalling. Finally, a range of potential regulatory proteins and putative downstream signalling substrates have been identified for various RLKs. Despite some similarities with animal receptor kinase signalling systems, mechanisms that affect the intracellular behaviour, regulation and interactions of RLKs appear to be very diverse, potentially explaining how signalling specificity is maintained at the cytoplasmic level.

Arabidopsis↗
PubMed2006

Novel signals for plant development.

Classic signal molecules such as auxin, cytokinin, gibberellins, abscisic acid and more recently brassinosteroids have been extensively studied in the context of their role in morphogenetic processes in plants. In the past five years, it has become apparent that there are novel signaling molecules, such as N-acylethanolamides, alkamides, glutamate and nitric oxide, that might play important roles in the regulation of morphogenetic and adaptive processes. There is information pointing out that these molecules might be involved in diverse processes, including seed germination, pathogenesis, modulation of plant architecture and response to abiotic factors. In animals, alkamides and N-acylethanolamides act as endogenous signaling molecules that activate cannabinoid receptors, which are coupled to signal transduction cascades involving glutamate and nitric oxide. Hence, there is a possibility that cannabinoid signaling represents an evolutionary conserved pathway that modulates cellular and physiological processes in eukaryotes.

Amides↗
PubMed2006

Common regulatory themes in meristem development and whole-plant homeostasis.

The maintenance of meristems throughout plant ontogeny allows the development of a diversity of structural forms from the same genetic base. Examination of the common and contrasting features of these meristems leads to the outline of common regulatory themes in meristem development. In particular, by including comparisons with embryogenesis research, we see that hormones and factors that are generally attributed roles in stress response, such as redox potential, carotenoids, flavonoids, brassinosteroids, jasmonic acid and ethylene, are emerging as major candidates for long-distance or short-distance signalling molecules in meristem development. In each case, hormone response appears to be influenced greatly by the developmental window or transition stage at which the meristem resides.

Homeostasis↗
PubMed2003

AXR1 is involved in BR-mediated elongation and SAUR-AC1 gene expression in Arabidopsis.

Limited information is available concerning the interactions between the brassinosteroid (BR) and auxin signaling pathways. The expression pattern of the SAUR-AC1 gene, an early auxin-inducible gene in Arabidopsis, was studied in response to brassinolide (BL), in the presence of a BR-biosynthesis inhibitor, in a BR-deficient mutant, and in combination with auxin. The results suggested that the SAUR-AC1 gene is regulated by BRs independently of auxin levels, and that it is important in BR-mediated elongation. The axr1 (auxin insensitive 1) mutant was less sensitive to BL-induced elongation and BL-induced SAUR-AC1 expression, suggesting that a ubiquitin ligase-mediated system is involved in BR-mediated elongation.

Arabidopsis↗
PubMed2001

Chromatographic procedures for the isolation of plant steroids.

In this review, we consider the general principles and specific methods for the purification of different classes of phytosteroids which have been isolated from plant sources: brassinosteroids, bufadienolides, cardenolides, cucurbitacins, ecdysteroids, steroidal saponins, steroidal alkaloids, vertebrate-type steroids and withanolides. For each class we give a brief summary of the characteristic structural features, their distribution in the plant world and their biological effects and applications. Most classes are associated with one or a few plant families, e.g., the withanolides with the Solanaceae, but others, e.g., the saponins, are very widespread. Where a compound class has been extensively studied, a large number of analogues are present across a range of species. We discuss the general principles for the isolation of plant steroids. The predominant methods for isolation are solvent extraction/partition followed by column chromatography and thin-layer chromatography/HPLC.

Plants↗
PubMed2001

Synthesis and bioactivity of natural and C-3 fluorinated biosynthetic precursors of 28-homobrassinolide.

In this paper we describe the synthesis of two new fluorinated brassinosteroids: (22R,23R)-22,23-dihydroxy-3alpha-fluorostigmastan-6-one and (22R,23R)-22,23-dihydroxy-3beta-fluorostigmastan-6-one. Their bioactivities were evaluated in the rice lamina inclination test and compared with that of 28-homocastasterone, 28-homotyphasterol and 28-homoteasterone, possible biosynthetic precursors of 28-homobrassinolide. Results confirmed expected similarities between the biosynthesis of 24-ethylbrassinosteroids (named as the 28-homo series) and that described for 24-methylbrassinosteroids, and also indicated that these precursors might exhibit per se activities.

Cholestanones↗
PubMed2002

Biosynthesis of cholestanol in higher plants.

To understand the early steps of C(27) brassinosteroid biosynthesis, metabolic experiments were performed with Arabidopsis thaliana and Nicotiana tabacum seedlings, and with cultured Catharanthus roseus cells. [26, 28-2H(6)]Campestanol, [26-2H(3)]cholesterol, and [26-2H(3)]cholestanol were administered to each plant, and the resulting metabolites were analyzed by gas chromatography-mass spectrometry. In all the species examined, [2H(3)]cholestanol was identified as a metabolite of [2H(6)]campestanol, and [2H(3)]cholest-4-en-3-one and [2H(3)]cholestanol were identified as metabolites of [2H(3)]cholesterol. This study revealed that cholestanol (C(27) sterol) was biosynthesized from both cholesterol (C(27) sterol) and campestanol (C(28) sterol). It was also demonstrated that cholestanol was converted to 6-oxocholestanol, and campestanol was converted to 6-oxocampestanol.

Arabidopsis↗
PubMed2003

Biosynthesis of 2,3-epoxybrassinosteroids in seedlings of Secale cereale.

Two new brassinosteroids, (22R,23R,24S)-22,23-dihydroxy-24-methyl-5alpha-cholest-2-en-6-one (secasterol) and (22R,23R,24S)-22,23-dihydroxy-2alpha,3alpha-epoxy-24-methyl-5alpha-cholest-6-one (2,3-diepisecasterone) have been identified together with a known 2,3-epoxybrassinosteroid, secasterone, in seedlings of Secale cereale. Deuterated secasterol, teasterone, and typhasterol, upon administration to rye seedlings, were incorporated into secasterone and 2,3-diepisecasterone, indicating a biosynthetic route via teasterone/typhasterol to secasterol to 2,3-epoxybrassinosteroids.

Hydroxycholesterols↗
PubMed2000

Synthesis of 6-oxy functionalized campest-4-en-3-ones: efficient hydroperoxidation at C-6 of campest-5-en-3-one with molecular oxygen and silica gel.

As a reference compound library for the investigation of biosynthesis of brassinosteroids, focused on a pathway from campesterol (1) to campestanol (2), 6-oxy functionalized campest-4-en-3-ones as well as campest-5-en-3-one (7) and campestane-3,6-dione were prepared from 1. Oxidation of 1 with pyridinium chlorochromate buffered by calcium carbonate gave 5-en-3-one (7) in 76% yield. Treatment of 7 with silica gel under an oxygen atmosphere in ethyl ether at room temperature produced efficient hydroperoxidation at the C-6 position to give 6alpha-hydroperoxycampest-4-en-3-one and 6beta-hydroperoxycampest-4-en-3-one in 34% and 49% yields, respectively. These compounds were converted to 6alpha-hydroxycampest-4-en-3-one and 6beta-hydroxycampest-4-en-3-one by reduction with triethyl phosphite. This provided the first example of the practical use of hydroperoxidation at C-6 of a Delta(5(6))-unsaturated 3-oxo-steroid with molecular oxygen and silica gel. On the other hand, oxidation of 1 with pyridinium chlorochromate in the absence of calcium carbonate gave campest-4-ene-3,6-dione in 64% yield. This compound was then converted in a highly stereoselective manner to campestane-3,6-dione with A/B trans ring junction by reduction with titanium (III) chloride in 85% yield.

Biochemistry↗
PubMed2002

Spirostanic analogues of castasterone.

The synthesis, spectroscopic characterization, and biologic activity of two bioactive spirostanic analogues of the naturally occurring brassinosteroid castasterone are described.

Borohydrides↗
PubMed2002

Synthesis of hexadeuterated 23-dehydroxybrassinosteroids.

Two hexadeuterated brassinosteroids (BS) ([26,27-2H(6)]-23-dehydroxycastasterone and [26,27-2H(6)]-cathasterone) containing a hydroxy group at C(22) instead of the 22R,23R-diol function characteristic for most compounds of this class were prepared for biochemical studies. The corresponding non-deuterated compounds are considered intermediates in brassinolide biosynthesis. The carbon skeleton of the side chain with proper stereochemistry at C(24) was prepared from commercially available (2R)-3-hydroxy-2-methylpropanoate. This low molecular fragment was coupled to the tetracyclic steroidal fragment through the reaction of the appropriate sulfone with C(22) aldehyde. Formation of the necessary configuration of the 22-hydroxy group was achieved by hydride reduction of the corresponding ketone. Deuterium atoms at C(26) and C(27) originated from [2H(3)]methyl iodide used for alkylation of the intermediate sulfone.

Deuterium↗
PubMed2002

Repressors of photomorphogenesis.

The internal programs of plant development are informed in a profound way by environmental light conditions. This review summarizes the contribution of repressor proteins to the light-signaling machinery during seedling development, and discusses the integration of repressors with other, positively acting, light-signaling pathways and auxin and brassinosteroid hormone-signaling pathways. The main focus is placed on the mode of action of the COP/DET/FUS proteins, which were first identified in Arabidopsis but are now emerging in other plants. Their role in regulating protein turnover through ubiquitination is reviewed in light of parallel ongoing investigations of COP/DET/FUS homologues in metazoans and fungi.

Arabidopsis↗
PubMed2005

Gravitropic bending and plant hormones.

Gravitropism is a complex multistep process that redirects the growth of roots and various above-ground organs in response to changes in the direction of the gravity vector. The anatomy and morphology of these graviresponding organs indicates a certain spatial separation between the sensing region and the responding one, a situation that strongly suggests the requirement of phytohormones as mediators to coordinate the process. The Cholodny-Went hypothesis suggested auxin as the main mediator of gravitropism. So far, ample evidence has been gathered with regard to auxin asymmetrical detection, polar and lateral transport involving influx and efflux carriers, response signaling pathway, and possible modes of action in differential cell elongation, supports its major role in gravitropism at least in roots. However, it is becoming clear that the participation of other hormones, acting in concert with auxin, is necessary as well. Of particular importance is the role of ethylene in shoot gravitropism, possibly associated with the modulation of auxin transport or sensitivity, and the key role implicated for cytokinin as the putative root cap inhibitor that controls early root gravitropism. Therefore, the major advances in the understanding of transport and signaling of auxin, ethylene, and cytokinin may shed light on the possibly tight and complicated interactions between them in gravitropism. Not much convincing evidence has been accumulated regarding the participation of other phytohormones, such as gibberellins, abscisic acid, brassinosteroids, jasmonates, and salicylic acid, in gravitropism. However, the emerging concept of cooperative hormone action opens new possibilities for a better understanding of the complex interactions of all phytohormones and their possible synergistic effects and involvement in the gravitropic bending process.

Gravitropism↗
PubMed2001

Searching for the physiological function of 17beta-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus: studies of substrate specificity and expression analysis.

17beta-hydroxysteroid dehydrogenase from the filamentous fungus Cochliobolus lunatus (17beta-HSDcl) has recently been characterized. Since its function is still unclear, we performed substrate specificity studies to obtain some indications about its physiological function. Different steroids were studied as putative substrates of recombinant 17beta-HSDcl, androgens and estrogens, brassinosteroids, and the fungal steroid herbarulid. Among these androgens and estrogens were most efficiently converted. The following substrates in decreasing order were best reduced: 4-estrene-3,17-dione, 5alpha-androstane-3,17-dione, 4-androstene-3,17-dione and estrone. Two typical inhibitors were tested: carbenoxolone--a representative inhibitor of the SDR family and quercetin--a diagnostic inhibitor of carbonyl reductases. Among these two quercetin was more efficient. Expression studies revealed that 17beta-HSDcl is mainly expressed in the stationary phase of growth indicating its possible involvement in secondary metabolism.

17-Hydroxysteroid Dehydrogenases↗
PubMed2003

Making inroads into plant receptor kinase signalling pathways.

Cell-membrane-located receptor kinases play important roles in many plant signal-transduction pathways. Exciting progress has been made in recent years with the characterization of four ligand-receptor systems involved in physiological processes as diverse as self-pollen rejection, stem-cell maintenance and differentiation at the shoot meristem, the response to the brassinosteroid hormones and the innate response to bacterial pathogens. These new findings emphasize the remarkably high diversity of these signalling pathways, although some downstream components are shared. This observation supports the idea that the wide diversification of plant receptors is associated with a high degree of specialization, one receptor potentially regulating a single developmental process. However, the possibility that one receptor might have a dual recognition function cannot be ruled out.

Ligands↗
PubMed1998

Challenges in understanding RLK function.

Plants use receptor-like kinases (RLKs) to transduce extracellular signals into the cell. Recent advancements in RLK research include the cloning of the BRASSINOSTEROID INSENSITIVE 1 and CLAVATA 1 genes, revealing RLK roles in development. Our understanding of RLK function has also been broadened by transgenic approaches in the study of the RLKs pollen receptor kinase 1, and wall associated kinase 1. These results extend the observations that RLKs function in developmental processes and plant defense responses. Additionally, expression based studies suggest roles for other newly reported RLKs in development and light responses. Taken together, the studies confirm the importance of RLKs in diverse plant processes, yet major challenges remain. These include identifying ligands that activate RLKs and characterizing downstream pathways. These challenges can be conquered by coordinated efforts from investigators using molecular, genetic, and biochemical approaches.

Amino Acid Sequence↗
PubMed1989

Effects of potential inhibitors on Brugia pahangi in vitro: macrofilaricidal action and inhibition of microfilarial production.

A series of compounds that apparently disrupt hormonally regulated processes in insects have been examined for effects on the viability and microfilarial production of adult Brugia pahangi cultured in vitro. The azasteroids, 25-azacoprostane and 25-azacholestane, inhibited the production of microfilariae at 5 ppm, the former also exhibiting macrofilaricidal activity at this concentration. The brassinosteroids examined inhibited microfilarial production at 5 ppm but did not affect worm viability. Azadirachtin also proved to be a significant inhibitor of microfilarial release without effect on worm motility or viability. Of all the compounds tested, the non-steroidal amines appeared to be the most promising as potential filaricides, several of them proving to be macrofilaricidal at 1 ppm and affecting microfilarial production at even lower concentrations.

Amines↗