Action of Abscisic Acid on Auxin Transport and its Relation to Phototropism

The action of abscisic acid on the kinetics of auxin transport through Zea mays L. (cv. Goudster) coleoptiles has been investigated. Abscisic acid applied simultaneously with indoleacetic acid-2-¹⁴C in the donor block reduced the transport intensity without materially affecting the basipetal velocity or the uptake. No effect on acropetal transport was observed. The data have been used to discuss the similarities in effects of abscisic acid and visible radiation and a hypothesis is proposed to explain the phenomena of phototropism.     

Basipetal and Acropetal Auxin Transport in Relation with Temperature

In stem sections of lentil seedlings, there is a typical polar movement of IAA labelled with ¹⁴C. The degree of polarity, expressed as the ratio of basipetal to acropetal transport, was (25°C) 7.6. A decrease (from 25° to 15°C) and an increase (from 25° to 30°C) of temperature cause a reduction of the IAA uptake by the sections and a decrease of both the basipetal and the acropetal translocation of IAA. Results suggest that the basipetal as well as the acropetal movement of auxin, are dependent of a metabolical component which is discussed.     

Dependence of Basipetal Polar Transport of Auxin upon Aerobic Metabolism

The movement of IAA-¹⁴C through coleoptile segments of Avena and Zea has been investigated under aerobic and anaerobic conditions. The results are as follows: Zea. Using a 5-mm segment and a 2-hour transport period anaerobic conditions reduced the total uptake of ¹⁴C from an apical donor by 74% and the proportion of the total found in the receiving block by at least 45%. Anaerobic conditions reduced total uptake from a basal donor by 58% but no ¹⁴C reached the apical receiving block in either air or N₂. Uptake from apical and basal donor blocks in N₂ is closely similar.

The presence of ¹⁴C in the basal receiving blocks, and its absence in the apical receiving blocks, in N₂ suggests that even in anaerobic conditions movement of IAA is polarized basipetally, although the movement occurs at only a fraction of the rate found in air.

Anaerobic conditions induced a similar reduction in basipetal movement of IAA in upper and lower 5-mm segments taken from the apical 10 mm of a Zea coleoptile.

Using 10-mm Zea segments no ¹⁴C was recovered in the receiving blocks at the basal end of the segment after 2 and 4 hours in N₂ whereas large amounts were recovered in air.

Avena: Using 5-mm segments and a 2-hour transport period the total uptake of ¹⁴C from an apical donor is reduced by 83%. Movement of ¹⁴C into the basal donor is totally inhibited in N₂. Total uptake of ¹⁴C from a basal donor is reduced by 61% in nitrogen and no ¹⁴C reached the apical receiving blocks regardless of the atmospheric conditions.

A time course for the movement of ¹⁴C into the basal and apical receiving blocks through 5-mm segments showed that in air the amount in the basal receivers increased for 4 hours and then remained approximately uniform. In N₂ no significant ¹⁴C reached the receivers until 6 to 8 hours after the application of donors but even then the amounts were about 12 to 14% of that in aerobic receivers. Movement of ¹⁴C into apical receivers was similar in air and in nitrogen and even after 6 to 8 hours the amount of radioactivity barely reached significant levels.

     

Rhythmicity in the Basipetal Transport of Indoleacetic Acid through Coleoptiles

¹⁴C-Indoleacetic acid was applied to coleoptiles of corn (Zea mays) and oat (Avena sativa). The coleoptiles were detached from the endosperms at 6-minute intervals after indoleacetic acid application, and the radioactivity was determined in successive 2-millimeter regions. The rate (per cent per minute) of basipetal transport of indoleacetic acid is periodic in various regions of the coleoptile, with a period of about 20 minutes. The possible relation of this cyclic phenomenon to other rhythmic processes of similar periodicities is discussed. A distinct acropetal transport (against the concentration gradient) from the subapical region to the apical 2-millimeter region of the coleoptile was detected.     

Auxin Stimulation of Cambial Activity in Pinus silvestris II. Dependence upon Basipetal Transport

Natural auxin content has been determined in the cambial region of large Pinus silvestris L. trees at various dates during the year. The tissue was collected from the stem of intact or ring-barked trees and from stumps remaining after the trees were cut down at breast height in early summer or late autumn. No seasonal decrease of concentration of the extractable auxin in the cambial region could be detected. Decapitation or ring-barking produced severe reduction in auxin content and arrested cambial division. In the next season the auxin level and the cambial activity remained completely depressed. It is concluded that without tissue continuity in the region external to xylem and without basipetal supply of substances, no mechanism operated by roots or remaining stem tissue near the tree base can ensure a high level of auxin in the cambial region or activate and maintain the cambial division. The activity of extracted pine auxin was found not to be identical with the stimulatory potential of authentic IAA determined by standard bioassays. The possibility of interaction with other extracted substances is discussed.     

Action of Abscisic Acid on Ion Transport as Affected by Root Temperature and Nutrient Status

Measurements were made of the transport of ions through excisedbarley roots. It is shown that addition of 10^–5 M abscisicacid (ABA) may lead to inhibition or stimulation of transport.The effect of ABA depended on the conditions in which the plantshad been grown and on the temperature at which the experimentwas carried out. It is suggested that stimulation of transportis a direct effect of ABA, but inhibition may be an indirecteffect due to disturbance of endogenous levels of plant hormones.The results are considered in relation to regulation of iontransport in the plant as a whole.     

The Formation of Structural Abnormalities in Karelian Birch Wood is Associated with Auxin Inactivation and Disrupted Basipetal Auxin Transport

Journal of Plant Growth Regulation - Figured wood of Karelian birch (Betula pendula Roth var. carelica (Merckl.) Hämet-Ahti) is highly appraised for its ornamental properties. The reasons for...     

Abscisic Acid Transport in Human Erythrocytes

Abscisic acid (ABA) is a plant hormone involved in the response to environmental stress. Recently, ABA has been shown to be present and active also in mammals, where it stimulates the functional activity of innate immune cells, of mesenchymal and hemopoietic stem cells, and insulin-releasing pancreatic β-cells. LANCL2, the ABA receptor in mammalian cells, is a peripheral membrane protein that localizes at the intracellular side of the plasma membrane. Here we investigated the mechanism enabling ABA transport across the plasmamembrane of human red blood cells (RBC). Both influx and efflux of [³H]ABA occur across intact RBC, as detected by radiometric and chromatographic methods. ABA binds specifically to Band 3 (the RBC anion transporter), as determined by labeling of RBC membranes with biotinylated ABA. Proteoliposomes reconstituted with human purified Band 3 transport [³H]ABA and [³⁵S]sulfate, and ABA transport is sensitive to the specific Band 3 inhibitor 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid. Once inside RBC, ABA stimulates ATP release through the LANCL2-mediated activation of adenylate cyclase. As ATP released from RBC is known to exert a vasodilator response, these results suggest a role for plasma ABA in the regulation of vascular tone.     

PINOID Kinase Regulates Root Gravitropism through Modulation of PIN2-Dependent Basipetal Auxin Transport in Arabidopsis

Reversible protein phosphorylation is a key regulatory mechanism governing polar auxin transport. We characterized the auxin transport and gravitropic phenotypes of the pinoid-9 (pid-9) mutant of Arabidopsis (Arabidopsis thaliana) and tested the hypothesis that phosphorylation mediated by PID kinase and dephosphorylation regulated by the ROOTS CURL IN NAPHTHYLPHTHALAMIC ACID1 (RCN1) protein might antagonistically regulate root auxin transport and gravity response. Basipetal indole-3-acetic acid transport and gravitropism are reduced in pid-9 seedlings, while acropetal transport and lateral root development are unchanged. Treatment of wild-type seedlings with the protein kinase inhibitor staurosporine phenocopies the reduced auxin transport and gravity response of pid-9, while pid-9 is resistant to inhibition by staurosporine. Staurosporine and the phosphatase inhibitor, cantharidin, delay the asymmetric expression of DR5∷revGFP (green fluorescent protein) at the root tip after gravistimulation. Gravity response defects of rcn1 and pid-9 are partially rescued by treatment with staurosporine and cantharidin, respectively. The pid-9 rcn1 double mutant has a more rapid gravitropic response than rcn1. These data are consistent with a reciprocal regulation of gravitropism by RCN1 and PID. Furthermore, the effect of staurosporine is lost in pinformed2 (pin2). Our data suggest that reduced PID kinase function inhibits gravitropism and basipetal indole-3-acetic acid transport. However, in contrast to PID overexpression studies, we observed wild-type asymmetric membrane distribution of the PIN2 protein in both pid-9 and wild-type root tips, although PIN2 accumulates in endomembrane structures in pid-9 roots. Similarly, staurosporine-treated plants expressing a PIN2∷GFP fusion exhibit endomembrane accumulation of PIN2∷GFP, but no changes in membrane asymmetries were detected. Our data suggest that PID plays a limited role in root development; loss of PID activity alters auxin transport and gravitropism without causing an obvious change in cellular polarity.A variety of important growth and developmental processes, including gravity response, embryo and vascular development, and the branching of roots and shoots, are controlled by the directional and regulated transport of auxin in higher plants. Reversible protein phosphorylation is an important regulatory strategy that may modulate auxin transport and dependent processes such as root gravitropism, perhaps through action of the PINOID (PID) kinase (for review, see DeLong et al., 2002; Galvan-Ampudia and Offringa, 2007). PID is an AGC family Ser/Thr kinase (Christensen et al., 2000) and belongs to an AGC kinase clade containing WAG1, WAG2, AGC3-4, and D6PK/AGC1-1 (Santner and Watson, 2006; Galvan-Ampudia and Offringa, 2007; Zourelidou et al., 2009). PID activity has been demonstrated in vitro and in vivo (Christensen et al., 2000; Michniewicz et al., 2007), and several pid mutant alleles exhibit altered auxin transport in the inflorescence and a floral development defect resembling that of auxin transport mutants (Bennett et al., 1995). Overexpression of the PID gene results in profound alterations in root development and responses to auxin transport inhibitors, reduced gravitropism and auxin accumulation at the root tip (Christensen et al., 2000; Benjamins et al., 2001; Michniewicz et al., 2007), as well as enhanced indole-3-acetic acid (IAA) efflux in tobacco (Nicotiana tabacum) cell cultures (Lee and Cho, 2006) and altered PINFORMED1 (PIN1), PIN2, and PIN4 localization patterns (Friml et al., 2004; Michniewicz et al., 2007), consistent with PID being a positive regulator of IAA efflux. However, the effects of pid loss-of-function mutations on auxin transport activities and gravitropic responses in roots have not yet been reported (Robert and Offringa, 2008).In contrast, auxin transport and gravitropism defects of a mutant with reduced protein phosphatase activity have been characterized in detail. The roots curl in naphthylphthalamic acid1 (rcn1) mutation, which ablates the function of a protein phosphatase 2A regulatory subunit, causes reduced PP2A activity in vivo and in vitro (Deruère et al., 1999). Roots and hypocotyls of rcn1 seedlings have elevated basipetal auxin transport (Deruère et al., 1999; Rashotte et al., 2001; Muday et al., 2006), and rcn1 roots exhibit a significant delay in gravitropism, consistent with altered auxin transport (Rashotte et al., 2001; Shin et al., 2005). These data indicate that PP2A is a negative regulator of basipetal transport and suggest that if PID-dependent phosphorylation regulates root auxin transport and gravitropism, then it may act in opposition to PP2A-dependent dephosphorylation.In roots, auxin transport is complex, with distinct sets of influx and efflux carriers that define tissue-specific and opposing directional polarities (for review, see Leyser, 2006). IAA moves acropetally, from the shoot toward the root apex, through the central cylinder (Tsurumi and Ohwaki, 1978), and basipetally, from the root apex toward the base, through the outer layer of cells (for review, see Muday and DeLong, 2001). When plants are reoriented relative to the gravity vector, auxin becomes asymmetrically distributed across the root tip, as a result of a process termed lateral auxin transport (for review, see Muday and Rahman, 2008). Several carriers that mediate root basipetal IAA transport have been clearly defined and include the influx carrier AUXIN-INSENSITIVE1 (AUX1; Marchant et al., 1999; Swarup et al., 2004; Yang et al., 2006) and efflux carriers of two classes, PIN2 (Chen et al., 1998; Müller et al., 1998; Rashotte et al., 2000) and ATP-BINDING CASSETTE TYPE B TRANSPORTER4/MULTIDRUG-RESISTANT4/P-GLYCOPROTEIN4 (ABCB4/MDR4/PGP4; Geisler et al., 2005; Terasaka et al., 2005; Lewis et al., 2007). Lateral transport at the root tip may be mediated by PIN3, an efflux carrier with a gravity-dependent localization pattern (Friml et al., 2002; Harrison and Masson, 2007).Gravitropic curvature of Arabidopsis (Arabidopsis thaliana) roots requires changes in IAA transport at the root tip (for review, see Muday and Rahman, 2008). Auxin transport inhibitors (Rashotte et al., 2000) and mutations in genes encoding basipetal transporters, including aux1 (Bennett et al., 1996), pin2/agr1 (Chen et al., 1998; Müller et al., 1998), and abcb4/mdr4/pgp4 (Lin and Wang, 2005; Lewis et al., 2007), alter gravitropism. Auxin-inducible reporters exhibit asymmetric expression across the root tip prior to differential growth, and this asymmetry is abolished by treatment with auxin transport inhibitors that prevent gravitropic curvature (Rashotte et al., 2001; Ottenschläger et al., 2003). Additionally, the pin3 mutant exhibits slightly reduced rates of gravitropic curvature (Harrison and Masson, 2007), and PIN3 is expressed in the columella cells, which are the site of gravity perception (Blancaflor et al., 1998; Friml et al., 2002). The PIN3 protein relocates to membranes on the lower side of columella cells after gravitropic reorientation, consistent with a role in facilitating asymmetric IAA transport at the root tip (Friml et al., 2002; Harrison and Masson, 2007).The available data suggest a model in which PID and RCN1 antagonistically regulate basipetal transport and gravitropic response in root tips (Fig. 1). In this model, the regions with the highest IAA concentrations in the epidermal and cortical cell layers are indicated by shading, and the arrows indicate the direction and relative amounts of basipetal auxin transport. Our previous work suggests that elevated basipetal IAA transport in rcn1 roots impairs gravitropic response, presumably due to the inability of roots either to form or to perceive a lateral auxin gradient in the context of a stronger polar IAA transport stream (Rashotte et al., 2001). Enhanced basipetal transport may increase the initial auxin concentration along the upper side of the root, impeding the establishment or perception of a gradient in rcn1 and cantharidin-treated wild-type roots (Fig. 1, right). Based on the published pid inflorescence transport data (Bennett et al., 1995), we hypothesize that pid seedling roots and staurosporine-treated wild-type roots have reduced basipetal auxin transport (Fig. 1, left). Upon reorientation of roots relative to the gravity vector, the reduced basipetal IAA transport in pid may lead to slower establishment of an auxin gradient across the root. This model then predicts that cantharidin treatment of pid-9 or staurosporine treatment of rcn1 seedlings would enhance or restore gravitropism in these mutants. Similarly, a double mutant might be expected to exhibit a corrected gravitropic response relative to the single mutants.Open in a separate windowFigure 1.Auxin transport defects in pid-9 and rcn1 mutants alter auxin redistribution after reorientation relative to the gravity vector. This model predicts that differences in basipetal auxin transport activities of wild-type, pid-9, and rcn1 roots will affect the formation of lateral auxin gradients. The shaded area in each root represents the region of highest IAA concentration in epidermal and cortical cells, with darker shading in the central columella cells, believed to be the auxin maxima. The direction and amount of basipetal IAA transport are indicated by arrows. The region of differential growth during gravitropic bending is indicated by the shaded rectangle. If auxin transport is reduced (as shown in the pid-9 mutant or in staurosporine-treated seedlings), this would lead to a slower formation of an auxin gradient in root tips. The rcn1 mutation (or treatment with cantharidin) has already been shown to lead to increased basipetal transport and a reduced rate of gravitropic bending, consistent with altered formation or perception of an auxin gradient. The antagonistic effects of kinase and phosphatase inhibition are predicted to lead to normal gravity responses in the pid-9 rcn1 double mutant as well as in pid-9 and rcn1 single mutants treated with the “reciprocal” inhibitor.The experiments described here were designed to test this model by examining gravitropism and root basipetal IAA transport in pid and staurosporine-treated seedlings. We investigated the regulation of gravity response by PID kinase and RCN1-dependent PP2A activities and observed antagonistic interactions between the rcn1 and pid-9 loss-of-function phenotypes that are consistent with reciprocal kinase/phosphatase regulation. We found that loss of kinase activity in the pid mutant and in staurosporine-treated wild-type plants inhibits basipetal auxin transport and the dependent physiological process of root gravitropism. Our results suggest that staurosporine acts to regulate these processes through inhibition of PID kinase and that PID effects are PIN2 dependent. In both wild-type and pid-9 roots, we observed polar membrane distribution of the PIN2 protein; unlike wild-type roots, though, pid-9 roots exhibited modest accumulation of PIN2 in endomembrane structures. Similarly, we detected asymmetric distribution and endomembrane accumulation of PIN2∷GFP in staurosporine-treated roots. Our data suggest that PID plays a limited role in root development; loss of PID activity alters PIN2 trafficking, auxin transport, and gravitropism without causing an obvious loss of cellular polarity. Together, these experiments provide insight into phosphorylation-mediated control of the gravity response and auxin transport in Arabidopsis roots.     

Abscisic Acid, Auxin, and Ethylene in Explant Abscission

Experiments with explants of Phaseolus vulgaris L., cv. CanadianWonder, show that abscission and the associated rise in oarboxymethyl-cellulaseactivity in the separation zone are initiated by a peak in ethyleneproduction during senescence of pulvinar tissue distal to thezone. Distal applications of abscisic acid (ABA) induce an earlierpeak in ethylene production, increase cellulase activity, andpromote abscission. ABA is more effective in these ways if treatmentis delayed from 0 to 24 h after excision. With increasing concentrations of ABA the maximum rate of ethylene production is achievedsooner. Indol-3yl-acetic acid (IAA) and ABA are antagonisticin this system and have opposing effects. IAA retards the timeof peak ethylene-production and delays abscission. Explantsmay be retained for long periods without abscinding if incubatedin an ethylene-free atmosphere: the addition of ethylene forany one 24-h period (except the first 24 h after excision) willinduce abscission. The initial period of insensitivity to ethyleneis extended by distal applications of IAA. Ethylene-inducedabscission can be inhibited by IAA applied up to 72 h afterexcision provided the ethylene is not applied first. It is proposedthat abscission in the explant is controlled at two levels:(1) an auxin-dependent stage determining the duration of insensitivityto ethylene; (2) the timing of a rise in ethylene productionin senescing tissue distal to the separation zone. An auxin-ethylenebalance-mechanism at the separation zone is discussed.     

The Effect of Auxin and Abscisic Acid on the Catabolism of RNA

Abscisic acid (ABA) reduced growth in a root test (lentil),but the inhibition observed was less noticeable than that producedby using indol-3yl-acetic acid (IAA) alone. When both ABA andIAA were employed together, ABA acted as a growth-antagonistof IAA. ABA produced a strong inhibition of the total RNA accumulationand accelerated the RNase activity, while IAA strongly stimulatedthe RNA accumulation and greatly inhibited RNase activity. WhenABA and IAA were tested together, ABA also acted as an antagonistof TAA.     

Auxin, Gibberellin, Cytokinin and Abscisic Acid Production in Some Bacteria

Summary In this study, auxin (indole-3-acetic acid), gibberellin, cytokinin (zeatin) and abscisic acid production were investigated in the culture medium of the bacteria Proteus mirabilis, P. vulgaris, Klebsiella pneumoniae, Bacillus megaterium, B. cereus, Escherichia coli. To determine the levels of these plant growth regulators, high performance liquid chromatography (HPLC) technique was used. Our findings show that the bacteria used in this study synthesized the plant growth regulators, auxin, gibberellin, cytokinin and abscisic acid.     

PIN-Dependent Auxin Transport: Action,Regulation, and Evolution

Auxin participates in a multitude of developmental processes, as well as responses to environmental cues. Compared with other plant hormones, auxin exhibits a unique property, as it undergoes directional, cell-to-cell transport facilitated by plasma membrane-localized transport proteins. Among them, a prominent role has been ascribed to the PIN family of auxin efflux facilitators. PIN proteins direct polar auxin transport on account of their asymmetric subcellular localizations. In this review, we provide an overview of the multiple developmental roles of PIN proteins, including the atypical endoplasmic reticulum-localized members of the family, and look at the family from an evolutionary perspective. Next, we cover the cell biological and molecular aspects of PIN function, in particular the establishment of their polar subcellular localization. Hormonal and environmental inputs into the regulation of PIN action are summarized as well.     

The Role of Basipetal Auxin Transport in the Positional Control of Abscission Sites Induced in Impatiens sultani Stem Explants

If segments of Impatiens sultani stem are explanted and incubated,separation layers often form across them and lead to abscission.To test the suggested role of auxin concentration in controllingthe position of abscission sites, explants were labelled byapplying [¹⁴C]IAA to the shoot tip 4 h prior to explanting;transport of auxin applied in this way seems to resemble thatof endogenous auxin. During subsequent incubation of explantsfor 20 h, basipetal transport resulted in ¹⁴C accumulating justabove the base of the explants (nearly 80 % in the bottom 4mm of 24 mm explants). In internodal explants that had beenwounded at explanting by incising one side so as to sever avascular bundle, and in nodal explants with the leaf removed,the ¹⁴C also accumulated just above the wound or node to abouttwice the concentration otherwise expected; this accumulationwas probably due to basipetal transport being impeded by vasculardiscontinuity at the wound or node. Accumulation just abovethe base, or above a wound or node, resulted in gradients of¹⁴C concentration (presumably reflecting endogenous auxin concentration)decreasing in the morphologically upward direction at each ofthese three positions where abscission sites tend to occur. Impatiens sultani, abscission, auxin, IAA, node, polarized transport, positional control, separation layer, wounding     

Control of Ribonuclease and Acid Phosphatase by Auxin and Abscisic Acid during Senescence of Rhoeo Leaf Sections

We report the effects of abscisic acid and auxin (α-naphthalene acetic acid) on regulation of enzyme synthesis during senescence of leaf sections of Rhoeo discolor Hance. Abscisic acid always accelerates the onset of and enhances the magnitude of the increase in activity of acid phosphatase; this is followed by an acceleration of the onset of a rapid increase in free space.     

Studies on Abscisic Acid

Methyl α-cyclocitrylideneacetate was successively oxidized with selenium dioxide and chromium trioxide-pyridine complex to give methyl 1′-hydroxy-α-cyclocitrylideneacetate and a mixture of methyl 3′-keto-β-cyclocitrylideneacetate and methyl 4′-keto-α-cyclocitrylideneacetate. Further, oxidation of methyl α-cyclocitrylideneacetate with tert-butyl chromate afforded methyl 4′-keto-α-cyclocitrylideneacetate and methyl 1′-hydroxy-4′-keto-α-cyclocitry-lineacetate. Similarly, methyl α-cyclogeranate was oxidized to methyl 3-keto-β-cyclogeranate and methyl 4-keto-α-cyclogeranate. Methyl l′-hydroxy-4′-keto-α-cyclocitrylideneacetate, methyl l-hydroxy-4-keto-α-cyclogeranate and their related compounds did not show growth inhibitory activities on rice seedlings.     

Studies on Abscisic Acid

Epoxidation of methyl dehydro-β-ionylideneacetates with perbenzoic acid afforded methyl 1′, 2′-epoxy-dehydro-β-ionylideneacetates and then methyl 1′, 2′-, 3′, 4′-di-epoxy-dehydro-β-ionylideneacetates. 1′,2′-Epoxy-dehydro-β-ionone, obtained byepoxidation of dehydro-β-ionone, was treated with carbethoxymethylenetriphenlphosphorane to give ethyl 1′, 2′-epoxy-dehydro-β-ionylideneacetates. Further, sensitive photooxidation of ethyl dehydro-β-ionylidenecrotonate, followed by alkaline hydrolysis, gave 1′-hydroxy-4′-keto-α-ionylidenecrotonic acid. Growth inhibitory activities of the above compounds on rice seedlings were examined.