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At least 1,693 records · Page 94Linked to original sources
PubMed1987

Membrane-directed effects of the plant hormones abscisic acid, indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid.

This study examines two ways plant hormones might influence membrane processes, effects on overall permeability and modifications of specific ion channels. Abscisic acid (ABA) and indole-3-acetic acid (IAA) greatly enhanced erythritol permeability in mixed egg lecithin bilayers. In single component dioleoylphosphatidylcholine bilayers ABA was less effective than IAA, while 2,4-dichlorophenoxyacetate (2,4-D) did not affect either system or alter their ABA response. In Myxicola axons ABA and IAA had no effect, while 2,4-D (10 uM) caused a depolarizing shift of voltage-dependent Na+ and K+ activation by 25 +/- 4 mV and 15 +/- 3 mV, consistent with internal negative surface charge changes of -0.002 e-/A2 and -0.0007 e-/A2. We conclude that both generalized and ion channel-directed effects may link plant hormones and intracellular regulation.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1990

Effects of abscisic acid and xanthoxin on elongation and gravitropism in primary roots of Zea mays.

We examined the involvement of abscisic acid (ABA) and xanthoxin (Xan) in maize root gravitropism by (1) testing the ability of ABA to allow positive gravitropism in dark-grown seedlings of the maize cultivar LG11, a cultivar known to require light for positive gravitropism of the primary root, (2) comparing curvature in roots in which half of the cap had been excised and replaced with agar containing either ABA or indole-3-acetic acid (IAA), (3) measuring gravitropism in roots of seedlings submerged in oxygenated solutions of ABA or IAA and (4) testing the effect of Xan on root elongation. Using a variety of methods of applying ABA to the root, we found that ABA did not cause horizontally-oriented primary roots of dark-grown seedlings to become positively gravitropic. Replacing half of the root cap of vertically oriented roots with an agar block containing ABA had little or no effect on curvature relative to that of controls in which the half cap was replaced by a plain agar block. Replacement of the removed half cap with IAA either canceled or reversed the curvature displayed by controls. When light-grown seedlings were submerged in ABA they responded strongly to gravistimulation while those in IAA did not. Xan (up to 0.1 mM) did not affect root elongation. The results indicate that ABA is not a likely mediator of root gravitropism and that the putative ABA precursor, Xan, lacks the appropriate growth-inhibiting properties to serve as a mediator of root gravitropism.

Abscisic Acid↗
PubMed1993

Generation of electronically excited triplet species at the cellular level: a potential source of genotoxicity.

Selected enzymatic systems can efficiently produce a product in the electronically excited triplet state. Earlier, only the formation of electronically excited singlet species was known. The formation of triplet species has been demonstrated with both normal substrates/metabolites and with xenobiotics, even at the cellular level. Triplet excited species have intrinsically much longer lifetimes than excited singlets, whereby they can be potentially important agents for normal and/or deleterious processes, including mutagenesis. Enzymically generated triplet species can damage DNA, even when protein coated, as in the case of the lambda-phage of Escherichia coli. Some evidence of damage by triplet species has also been reported for intact cells. Triplet excited species may produce their effects through type I and/or type II dark photosensitization, that is, the events may be started by H abstraction and/or singlet oxygen/superoxide ion production. The induction of lipid peroxidation, with concomitant clastogenic effects, appears to be of special importance.

Acetaldehyde↗
PubMed2006

The Janus face of ethylene: growth inhibition and stimulation.

The gaseous plant hormone ethylene modulates many internal processes and growth responses to environmental stimuli. Ethylene has long been recognized as a growth inhibitor, but evidence is accumulating that ethylene can also promote growth. Therefore, the concept of ethylene as a general growth inhibitor needs reconsideration: a close examination of recent literature can help to understand the two contrasting faces of growth control by ethylene. Here, we propose a hypothesis that integrates growth inhibition and growth stimulation into one biphasic ethylene response model. Focusing on photosynthesis and cell expansion, we highlight several mechanisms through which ethylene affects plant growth, thereby interacting with various other signal transduction routes.

Abscisic Acid↗
PubMed2003

Molecular cloning and characterization of an amidase from Arabidopsis thaliana capable of converting indole-3-acetamide into the plant growth hormone, indole-3-acetic acid.

Acylamidohydrolases from higher plants have not been characterized or cloned so far. AtAMI1 is the first member of this enzyme family from a higher plant and was identified in the genome of Arabidopsis thaliana based on sequence homology with the catalytic-domain sequence of bacterial acylamidohydrolases, particularly those that exhibit indole-3-acetamide amidohydrolase activity. AtAMI1 polypeptide and mRNA are present in leaf tissues, as shown by immunoblotting and RT-PCR, respectively. AtAMI1 was expressed from its cDNA in enzymatically active form and exhibits substrate specificity for indole-3-acetamide, but also some activity against L-asparagine. The recombinant enzyme was characterized further. The results show that higher plants have acylamidohydrolases with properties similar to the enzymes of certain plant-associated bacteria such as Agrobacterium-, Pseudomonas- and Rhodococcus-species, in which these enzymes serve to synthesize the plant growth hormone, indole-3-acetic acid, utilized by the bacteria to colonize their host plants. As indole-3-acetamide is a native metabolite in Arabidopsis thaliana, it can no longer be ruled out that one pathway for the biosynthesis of indole-3-acetic acid involves indole-3-acetamide-hydrolysis by AtAMI1.

Amidohydrolases↗
PubMed2001

Auxin binding protein: curiouser and curiouser.

Auxin is implicated in a variety of plant developmental processes, yet the molecular mechanism of auxin response remains largely unknown. Auxin binding protein 1 (ABP1) mediates cell expansion and might be involved in cell cycle control. Structural modeling shows that it is a beta-barrel dimer, with the C terminus free to interact with other proteins. We do not know where ABP1 performs its receptor function. Most ABP1 is detected within the endoplasmic reticulum but the evidence indicates that it functions at the plasma membrane. ABP1 is established as a crucial component of auxin signaling, but its precise mechanism remains unclear.

Amino Acid Sequence↗
PubMed1999

Changes in hormonal balance and meristematic activity in primary root tips on the slowly rotating clinostat and their effect on the development of the rapeseed root system.

The morphometry of the root system, the meristematic activity and the level of indole-3-acetic acid (IAA), abscisic acid (ABA) and zeatin in the primary root tips of rapeseed seedlings were analyzed as functions of time on a slowly rotating clinostat (1 rpm) or in the vertical controls (1 rpm). The fresh weight of the root system was 30% higher throughout the growth period (25 days) in clinorotated seedlings. Morphometric analysis showed that the increase in biomass on the clinostat was due to greater primary root growth, earlier initiation and greater elongation of the secondary roots, which could be observed even in 5-day-old seedlings. However, after 15 days, the growth of the primary root slowed on the clinostat, whereas secondary roots still grew faster in clinorotated plants than in the controls. At this time, the secondary roots began to be initiated closer to the root tip on the clinostat than in the control. Analysis of the meristematic activity and determination of the levels in IAA, ABA and zeatin in the primary root tips demonstrated that after 5 days on the clinostat, the increased length of the primary root could be the consequence of higher meristematic activity and coincided with an increase in both IAA and ABA concentrations. After 15 days on the clinostat, a marked increase in IAA, ABA and zeatin, which probably reached supraoptimal levels, seems to cause a progressive disturbance of the meristematic cells, during a decrease of primary root growth between 15 and 25 days. These modifications in the hormonal balance and the perturbation of the meristematic activity on the clinostat were followed by a loss of apical dominance, which was responsible for the early initiation of secondary roots, the greater elongation of the root system and the emergence of the lateral roots near the tip of the primary root.

Abscisic Acid↗
PubMed1994

K+ channels of stomatal guard cells: bimodal control of the K+ inward-rectifier evoked by auxin.

The influence of the auxins indole-3-acetic acid (IAA) and 1-napthylene acetic acid (NAA) on K+ channels and their control was examined in stomatal guard cells of Vicia faba L. intact guard cells were impaled with multibarrelled microelectrodes to record membrane potentials and to monitor K+ channel currents under voltage clamp during exposures to 0.1-100 microM IAA and NAA. Following impalements, challenge with either IAA or NAA in the presence of 10 mM KCl resulted in the concerted modulation of at least four different currents with distinct kinetic characteristics and concentration dependencies. Equivalent concentrations of benzoic acid were wholly without effect. Most striking, current carried by inward-rectifying K+ channels (IK,in) exhibited a bimodal response to both IAA and NAA which was reversed on washing the auxins from the bathing medium. The steady-state current was augmented 1.3- to 2-fold at concentrations between 0.1 and 10 microM and antagonized at concentrations near 30 microM and above. Auxin agonism of IK,in was time- and voltage-independent. By contrast, IK,in inactivation at the higher auxin concentrations was marked by a voltage-dependence and slowing of the kinetics for current activation. Inactivation of IK,in by the auxins was relieved when cytoplasmic pH (pHi) was clamped near 7.0 in the presence of 30 mM Na(+)-butyrate. In addition to the control of IK,in, current carried by a second class of (outward-rectifying) K+ channels rose in a monotonic and largely voltage-independent manner with auxin concentrations about 10 microM and above, and IAA and NAA also activated an inward-going current with a voltage dependence characteristic of guard cell anion channels. Further changes in background current were consistent with a limited activation of the H(+)-ATPase. Over the concentration range examined, the auxins evoked membrane hyperpolarizations and depolarizations of up to +/- 12-19 mV, depending on the free-running membrane potential prevailing before auxin additions. Prolonging exposures to 100 microM auxin beyond 3-5 min frequently elicited rapid transitions to voltages near EK as well as regenerative action potentials. However, in every case the voltage response was a predictable consequence of auxin action on the K+ channels and, at 100 microM auxin, on the anion current.(ABSTRACT TRUNCATED AT 400 WORDS)

Benzoates↗
PubMed1999

A novel immunological approach establishes that the auxin-binding protein, Nt-abp1, is an element involved in auxin signaling at the plasma membrane.

Interactions of a collection of monoclonal antibodies (mAbs) to the recombinant Nicotiana tabacum auxin-binding protein 1 (Nt-abp1) were extensively characterized using surface plasmon resonance. Dynamic interaction studies using combinations of Nt-abp1, synthetic peptides corresponding to conserved sequences within auxin-binding proteins, and the mAbs have shown that a number of the mAbs recognized discontinuous epitopes revealing the junction of distinct domains in the folded protein. In particular, the two putative auxin binding domains and the C terminus of the protein were shown to interact with each other in the folded protein. Using the auxin-induced electrical response of tobacco protoplasts as a functional assay, all the mAbs exhibited either auxin antagonist or hormonomimetic properties. These effects, measured for the first time in homologous conditions, confirm that Nt-abp1 is present at the plasma membrane and is involved in the activation of the auxin-dependent electrical response of tobacco protoplasts. Based on our surface plasmon resonance data, we propose that the key event leading to the activation of this auxin electrical response consists of a conformational change in Nt-abp1.

Amino Acid Sequence↗