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At least 235 records · Page 13Linked to original sources
PubMed2001

Cell death of barley aleurone protoplasts is mediated by reactive oxygen species.

The barley aleurone layer is a terminally differentiated secretory tissue whose activity is hormonally controlled. The plant hormone gibberellic acid (GA) stimulates the secretion of hydrolytic enzymes and triggers the onset of programmed cell death (PCD). Abscisic acid (ABA) antagonizes the effects of GA and inhibits enzyme secretion and PCD. Reactive oxygen species (ROS) are key players in many types of PCD, and data presented here implicate ROS in hormonally regulated death of barley aleurone cells. Incubation of aleurone layers or protoplasts in H(2)O(2)-containing media results in death of GA-treated but not ABA-treated aleurone cells. Cells that are programmed to die are therefore less able to withstand ROS than cells that are programmed to remain alive. Illumination of barley aleurone protoplasts with blue or UV-A light results in a rapid increase in intracellular H(2)O(2) production. GA-treated protoplasts die rapidly in response to this increase in intracellular H(2)O(2) production, but ABA-treated protoplasts do not die. The rate of light-induced death could be slowed by antioxidants, and incubating protoplasts in the dark with the antioxidant butylated hydroxy toluene reduces the rate of hormonally induced death. Taken together, these data demonstrate that GA-treated aleurone protoplasts are less able than ABA-treated protoplasts to tolerate internally generated or exogenously applied H(2)O(2), and strongly suggest that ROS are components of the hormonally regulated cell death pathway in barley aleurone cells.

Abscisic Acid↗
PubMed2005

Two-component phosphorelay signal transduction systems in plants: from hormone responses to circadian rhythms.

One of the most fundamental and widespread mechanisms of signal perception/transduction in prokaryotes is generally referred to as the "two-component regulatory system (TCS)." The concept of TCS has already been introduced a decade ago from extensive studies on the model prokaryotic bacterium Escherichia coli. Results of recent studies on the model higher plant Arabidopsis thaliana have led us to learn a new scenario as to the versatility of TCS in eukaryotic species. In the plant, on the one hand, TCS are crucially involved in the signal transduction mechanism underlying the regulation of sophisticated plant development in response to hormones (e.g., cytokinin and ethylene). On the other hand, a unique TCS variant is essentially integrated into the plant clock function that generates circadian rhythms, and also tells us the time and season on this regularly spinning and revolving world. In this review, recent progress with regard to studies on TCS in higher plants will be discussed, focusing particularly on the model higher plant Arabidopsis thaliana.

Arabidopsis↗
PubMed2026

A group of TCP transcription factors is a missing link in strigolactone signaling.

Strigolactones (SLs) are plant-specialized butenolide signaling molecules, recognized as endogenous plant hormones, that control plant development and environmental adaptation. In Arabidopsis (Arabidopsis thaliana), the repressor D53-like SMXLs regulate the expression of a vast number of genes in an EAR-motif-dependent manner to mediate SL signaling. However, it remains unclear how the SMXLs are recruited to specific genes and implement unique functions in vivo. Based on chromatin co-distribution analysis, we constructed a chromatin co-localization map of SMXL6 with 108 transcription factors. Among the candidate transcription factors, the Class II TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP) family member TCP4 shows the highest frequency of chromatin co-localization with SMXL6. SMXL6 and TCP4 co‑localize at the promoter regions of 18 SL-induced SMXL6 target genes (SISGs), including BRC1. We confirmed that TCP4 interacts with SMXL6 and can bind directly to these co‑localized sites. The loss of CIN-TCPs function reduces the hormone responsiveness of the SL-induced genes. Introducing the tcp3/4/10 into SL‑deficient mutants restored the BRC1 expression to a level exceeding that of the wild type. However, the branching phenotype of the SL‑deficient mutant was only partially rescued, suggesting a limited role for BRC1 in SL‑mediated branching control and implicating the involvement of additional factors. An unexpected finding was that tcp3/4/10 rescued the dwarf phenotype of the SL‑deficient mutants, providing an opportunity to elucidate the mechanisms underlying SL‑regulated plant height. These findings demonstrate that TCP4 mediates SMXL6 chromatin recruitment during SL signaling, and provide a new understanding of how SMXL6 participates in SL signaling-mediated gene expression and plant development.

Lactones↗
PubMed1983

Gravitational effects on plant growth hormone concentration.

Numerous studies, particularly those of H. Dolk in the 1930's, established by means of bio-assay, that more growth hormone diffused from the lower, than from the upper side of a gravity-stimulated plant shoot. Now, using an isotope dilution assay, with 4,5,6,7 tetradeutero indole-3-acetic acid as internal standard, and selected ion monitoring-gas chromatography-mass spectrometry as the method of determination, we have confirmed Dolk's finding and established that the asymmetrically distributed hormone is, in fact, indole-3-acetic acid (IAA). This is the first physico-chemical demonstration that there is more free IAA on the lower sides of a geo-stimulated plant shoot. We have also shown that free IAA occurs primarily in the conductive vascular tissues of the shoot, whereas IAA esters predominate in the growing cortical cells. Now, using an especially sensitive gas chromatographic isotope dilution assay we have found that the hormone asymmetry also occurs in the non-vascular tissue. Currently, efforts are directed to developing isotope dilution assays, with picogram sensitivity, to determine how this asymmetry of IAA distribution is attained so as to better understand how the plant perceives the geo-stimulus.

Avena↗
PubMed1997

Recent developments in the field of plant steroid hormones.

Brassinolide and related brassinosteroids are a novel group of steroids which appear to be ubiquitous in plants. There is compelling evidence, particularly from recent genetic studies, that these steroids are essential for normal plant growth and development. Synthesis of brassinosteroids and aspects of their biochemistry are reviewed.

Brassinosteroids↗
PubMed2001

Plants steroid hormones, brassinosteroids: current highlights of molecular aspects on their synthesis/metabolism, transport, perception and response.

Brassinosteroids (BRs) are plant steroids essential for normal growth and development and can be defined as steroids that carry an oxygen moiety at C-3 and additional ones at one or more of the C-2, C-6, C-22 and C-23 carbon atoms. BR biosynthesis and metabolism mutants have been obtained and the corresponding genes cloned. These include genes encoding 5alpha-reductase and cytochrome P450 enzymes, that are similar to enzymes associated with mammalian steroid synthesis. Perception and/or response mutants have also been identified via screening for altered sensitivity to BRs. Some of these mutants have been found to be defective in a leucine-rich repeat receptor kinase and in a component of a vacuolar ATPase. This review highlights the recent advances in unraveling BR synthesis/metabolism, transport, perception and response through the analysis of BR mutants.

Biological Transport↗
PubMed1995

Cytokinins affect spore formation but not cell division in the yeast Saccharomyces cerevisiae.

Cytokinins are N6-substituted adenine derivatives that function as essential growth hormones in higher plants. In experimental systems, cytokinins can influence cell growth and differentiation among both plant and non-plant tissues. The single-celled yeast, Saccharomyces cerevisiae, has served as an effective and useful model system for the study of a wide range of cellular phenomena generally associated with higher eukaryotes, including mammals. In an attempt to assess the efficacy of its use to dissect the molecular basis for plant hormone action, the effects of cytokinins on S. cerevisiae with respect to cell division rates and sporulation efficiencies were monitored. While none of the cytokinins tested influenced mitotic generation times, micromolar concentrations of kinetin enhanced the formation of yeast haploid ascospores and even lower concentrations of isopentenyladenine inhibited ascus formation.

Adenine↗
PubMed2005

Arabidopsis KNOXI proteins activate cytokinin biosynthesis.

Plant architecture is shaped through the continuous formation of organs by meristems. Class I KNOTTED1-like homeobox (KNOXI) genes are expressed in the shoot apical meristem (SAM) and are required for SAM maintenance. KNOXI proteins and cytokinin, a plant hormone intimately associated with the regulation of cell division, share overlapping roles, such as meristem maintenance and repression of senescence, but their mechanistic and hierarchical relationship have yet to be defined. Here, we show that activation of three different KNOXI proteins using an inducible system resulted in a rapid increase in mRNA levels of the cytokinin biosynthesis gene isopentenyl transferase 7 (AtIPT7) and in the activation of ARR5, a cytokinin response factor. We further demonstrate a rapid and dramatic increase in cytokinin levels following activation of the KNOXI protein SHOOT MERISTEMLESS (STM). Application of exogenous cytokinin or expression of a cytokinin biosynthesis gene through the STM promoter partially rescued the stm mutant. We conclude that activation of cytokinin biosynthesis mediates KNOXI function in meristem maintenance. KNOXI proteins emerge as central regulators of hormone levels in plant meristems.

Arabidopsis↗
PubMed2006

Identification and functional analysis of bifunctional ent-kaurene synthase from the moss Physcomitrella patens.

ent-Kaurene is the key intermediate in biosynthesis of gibberellins (GAs), plant hormones. In higher plants, ent-kaurene is synthesized successively by copalyl diphosphate synthase (CPS) and ent-kaurene synthase (KS) from geranylgeranyl diphosphate (GGDP). On the other hand, fungal ent-kaurene synthases are bifunctional cyclases with both CPS and KS activity in a single polypeptide. The moss Physcomitrella patens is a model organism for the study of genetics and development in an early land plant. We identified ent-kaurene synthase (PpCPS/KS) from P. patens and analyzed its function. PpCPS/KS cDNA encodes a 101-kDa polypeptide, and shows high similarity with CPSs and abietadiene synthase from higher plants. PpCPS/KS is a bifunctional cyclase and, like fungal CPS/KS, directly synthesizes the ent-kaurene skeleton from GGDP. PpCPS/KS has two aspartate-rich DVDD and DDYFD motifs observed in CPS and KS, respectively. The mutational analysis of two conserved motifs in PpCPS/KS indicated that the DVDD motif is responsible for CPS activity (GGDP to CDP) and the DDYFD motif for KS activity (CDP to ent-kaurene and ent-16alpha-hydroxykaurene).

Alkyl and Aryl Transferases↗
PubMed2006

Transgenic rice plants ectopically expressing AtBAK1 are semi-dwarfed and hypersensitive to 24-epibrassinolide.

Brassinosteroids (BRs) are endogenous plant hormones essential for plant growth and development. Brassinosteroid insensitive1 (BRI1)-assocaiated receptor kinase (BAK1) is one of the key components in the BR signal transduction pathway due to its direct association with the BR receptor, BRI1. Although BRI1 and its orthologs have been identified from both dicotyledonous and monocotyledonous plants, less is known about BAK1 and its orthologs in higher plants other than Arabidopsis. This article provides the first piece of evidence that AtBAK1 can greatly affect growth and development of rice plants when ectopically expressed, suggesting that rice may share similar BR perception mechanism via BRI1/BAK1 complex. Interestingly, transgenic rice plants displayed semi-dwarfism and shortened primary roots. Physiological analysis and cell morphology assay demonstrated that the observed phenotypes in transgenic plants were presumably caused by hypersensitivity to endogenous levels of BRs, different from BR insensitive and deficient rice mutants. Consistently, several known BR inducible genes were also upregulated in transgenic rice plants, further suggesting that BAK1 was able to affect BR signaling in rice. On the other hand, the transgenic plants generated by overproducing AtBAK1 may potentially have agricultural applications because the dwarfed phenotype is generally resistant to lodging, while the fertility remains unaffected.

Agriculture↗
PubMed2004

Brassinosteroids interact with auxin to promote lateral root development in Arabidopsis.

Plant hormone brassinosteroids (BRs) and auxin exert some similar physiological effects likely through their functional interaction, but the mechanism for this interaction is unknown. In this study, we show that BRs are required for lateral root development in Arabidopsis and that BRs act synergistically with auxin to promte lateral root formation. BR perception is required for the transgenic expression of the beta-glucuronidase gene fused to a synthetic auxin-inducible promoter (DR5::GUS) in root tips, while exogenous BR promotes DR5::GUS expression in the root tips and the stele region proximal to the root tip. BR induction of both lateral root formation and DR5::GUS expression is suppressed by the auxin transport inhibitor N-(1-naphthyl) phthalamic acid. Importantly, BRs promote acropetal auxin transport (from the base to the tip) in the root. Our observations indicate that BRs regulate auxin transport, providing a novel mechanism for hormonal interactions in plants and supporting the hypothesis that BRs promote lateral root development by increasing acropetal auxin transport.

Arabidopsis↗
PubMed1997

ARF1, a transcription factor that binds to auxin response elements.

The plant hormone auxin regulates plant physiology by modulating the interaction of transcription factors with auxin response elements (AuxREs) of the affected genes. A transcription factor, Auxin Response Factor 1 (ARF1), that binds to the sequence TGTCTC in AuxREs was cloned from Arabidopsis by using a yeast one-hybrid system. ARF1 has an amino-terminal DNA-binding domain related to the carboxyl terminus of the maize transactivator Viviparous-1. Sequence requirements for ARF1 binding in vitro are identical to those that confer auxin responsiveness in vivo. The carboxyl terminus of ARF1 contains two motifs found in the Aux/IAA class of proteins and appears to mediate protein-protein interactions.

Amino Acid Sequence↗
PubMed1999

Cytokinin activation of Arabidopsis cell division through a D-type cyclin.

Cytokinins are plant hormones that regulate plant cell division. The D-type cyclin CycD3 was found to be elevated in a mutant of Arabidopsis with a high level of cytokinin and to be rapidly induced by cytokinin application in both cell cultures and whole plants. Constitutive expression of CycD3 in transgenic plants allowed induction and maintenance of cell division in the absence of exogenous cytokinin. Results suggest that cytokinin activates Arabidopsis cell division through induction of CycD3 at the G1-S cell cycle phase transition.

Adenine↗
PubMed2004

Identification of the bacterial alarmone guanosine 5'-diphosphate 3'-diphosphate (ppGpp) in plants.

Stringent control mediated by the bacterial alarmone guanosine 5'-diphosphate 3'-diphosphate (ppGpp) is a key regulatory process governing bacterial gene expression. By devising a system to measure ppGpp in plants, we have been able to identify ppGpp in the chloroplasts of plant cells. Levels of ppGpp increased markedly when plants were subjected to such biotic and abiotic stresses as wounding, heat shock, high salinity, acidity, heavy metal, drought, and UV irradiation. Abrupt changes from light to dark also caused a substantial elevation in ppGpp levels. In vitro, chloroplast RNA polymerase activity was inhibited in the presence of ppGpp, demonstrating the existence of a bacteria-type stringent response in plants. Elevation of ppGpp levels was elicited also by treatment with plant hormones jasmonic acid, abscisic acid, and ethylene, but these effects were blocked completely by another plant hormone, indole-3-acetic acid. On the basis of these findings, we propose that ppGpp plays a critical role in systemic plant signaling in response to environmental stresses, contributing to the adaptation of plants to environmental changes.

Chloroplasts↗
PubMed2005

Moderation of morphogenetic and oxidative stress responses in flax in vitro cultures by hydroxynonenal and desferrioxamine.

Hypocotyl segments of 7-day old seedlings of flax (Linum usitatissimum L.) cultivars Atalante, Flanders, Jitka, Szegedi 30 and Super were screened for organogenesis (shoot and root induction) and embryo-like structure production. A non-destructive assay for hydroxyl radicals (*OH), utilising DMSO as a radical trap, was used to determine *OH formation during tissue culture and morphogenesis. Desferrioxamine, an inhibitor of Fenton reaction, and 4-hydroxy-2-nonenal, a cytotoxic Lipid peroxidation product, were exogenously applied to flax cultures to determine the effect of antioxidative and prooxidative status on morphogenetic responses induced through the exogenous application of plant growth regulators. Flax genotypes varied in their response to treatments after exposure to different plant hormones. Hydroxyl radical (*OH) formation correlated with morphogenetic responses and this was affected by plant hormones. Desferrioxamine and 4-hydroxy-2-nonenal also moderated morphogenetic responses and influenced hydroxyl radical formation during in vitro propagation.

Aldehydes↗
PubMed2026

Transcriptome Analysis Reveals Key Drought-Stress-Responsive Genes in Two Bermudagrass Genotypes.

Drought inhibits grass development and survival. However, molecular-based studies on drought tolerance mechanisms in bermudagrass (Cynodon dactylon) remain scarce. Therefore, a drought-resistant bermudagrass (Tianshui) and a drought-sensitive (Zhengzhou) genotype were selected and subjected to 28 days of 50% drought stress. Leaves were sampled for RNA sequencing. Under drought stress, 2410 differentially expressed genes (DEGs) were discovered in which 1214 were upregulated (tolerant vs. sensitive) and 1196 downregulated. Kyoto Encyclopedia of Genes and Genomes (KEGG) indicated that these specific DEGs are notably present in hormonal signal transduction pathways, flavonoids biogenesis, carbohydrate metabolic processes, abscisic acid-mediated pathways, MAPK signaling, and gluconeogenesis. Additionally, the plant hormone signal transduction pathway is predominantly linked to abscisic acid signal transduction, and many other plant hormones were also drought-responsive. The study specifically targeted genes associated with the antioxidant enzyme system, with a particular emphasis on responsive TFs such as MYB, bHLH, bZIP, GRAS, and WRKY. This study establishes the theoretical framework and identifies gene sources for the genetic enhancement and breeding of bermudagrass in the future.

Cynodon↗