IAA Degradation Research Articles

Drought-protective effects of nutrient seed treatments during early growth of oilseed rape

Crop production is increasingly affected by water limitation even in temperate climates due to a rising frequency of drought periods, related with global change. The stress-protective nutrients, discussed as a mitigation strategy, were investigated for their potential drought-protective effects of nutrient seed treatments, based on Ca, K, Fe, Zn, Mn on early growth of oilseed rape (OSR). Responses were observed in five OSR hybrids under greenhouse conditions on two soils with contrasting properties (sandy-loam pH 5.6 vs. silty-loam pH 6.9) in two independent pot experiments. A 7-days drought period with reduced soil moisture level (40% soil water-holding capacity. WHC) inhibited shoot and root growth and caused irreversible wilting and leaf necrosis (27-46% of total leaf area) particularly on the sandy-loam with lower WHC, depending on the investigated genotype. Nutrient seed treatment increased shoot (10-15%) and particularly root growth (14-23%) as well as nutrient accumulation, but also reduced the proportion of irreversibly damaged leaves to 17-21%, with the largest effect in strongly drought-affected genotypes under the challenging conditions on the sandy-loam soil. Analysis of physiological stress indicators revealed increased accumulation of phenolics (23-28%), antioxidants (14-47%) and higher activities of ascorbate peroxidase (APX) (23-87%) in the leaf tissue, counteracting drought-induced oxidative stress. Moreover, APX activity was positively related with root length (R20.8953), suggesting a protective effect on drought-induced oxidative IAA degradation with inhibitory effects on root growth. Increased levels of absisic, jasmonic and salicylic acids during drought stress recovery point to stress priming effects, strengthening the natural adaptive responses to water limitation.

Evaluation of antioxidant supplementation in must on the development and potential reduction of different compounds involved in atypical ageing of wine using HPLC-HRMS

Atypical aging of white wines (ATA) is an off-flavour characterised by rapid loss of fruity aromas and the development of unpleasant odours.This study aims to evaluate the effectiveness of different oenological adjuvants (4-ethylcatechol, 4-methylcatechol, gentisic acid, hydroxytyrosol, ascorbic acid, glutathione, ellagic acid, gallic acid, galla tannin, ellagic tannin, quebracho, grape tannins) added to musts before fermentation for preventing the possible development of ATA. High resolution mass spectrometry made it possible to quantify and qualify free and conjugated IAA in wine at the end of the fermentation and subsequently 2-aminoacetophenone (AAP) was quantified after the force ageing period (6 days at 40 °C). Ascorbic acid was confirmed as the most appropriate antioxidant adjuvant which can be used for ATA defect prevention. With an almost comparable effect, gallotannin addition prevented AAP production to exceed 1 μg/L. A predicted model (ANCOVA) indicated that over 80% of the variability of potential AAP formation in wines was explained by the amount of precursors, grape variety and antioxidant treatment. Moreover, a suspect screening approach made it possible to study the kinetic formation and the consumption of the reaction metabolites formed during the oxidative degradation of IAA leading to AAP.

Profiles of endogenous ABA, bioactive GAs, IAA and their metabolites in Medicago truncatula Gaertn. non-embryogenic and embryogenic tissues during induction phase in relation to somatic embryo formation

Main conclusionDuring the 3-week-long induction phase, when M. truncatula cells leaf explants from non-embryogenic genotype (M9) and embryogenic variant (M9-10a) were forming the callus, biosynthesis and degradation of ABA, Gas and IAA proceeded at different levels. Induction of embryo formation is related to a lower ABA content, compared to the content of IAA and that of total bioactive GAs.Endogenous phytohormones are involved in the regulation of zygotic embryogenesis, but their role, especially of ABA, a plant growth inhibitor, in inducing somatic embryogenesis (SE) in angiosperms is still incompletely known. To arrive a better understanding of the ABA role in the process, we analyzed simultaneously and in detail changes in the contents of both ABA and five bioactive GAs (GA4, GA7, GA1, GA3, GA6) and IAA in M. truncatula non-embryogenic M9 (NE) and embryogenic M9-10a (E) genotypes. The initial leaf explants of both genotypes, and particularly NE, contained many times more ABA compared to the total bioactive GAs or IAA. In tissues during the entire 21-day induction all the hormones mentioned and their metabolites or conjugates were present; however, their contents were found to differ between the lines tested. The ABA level in primary explants of NE genotype was more than two times higher than that in E genotype. An even larger difference in the ABA content was found on the last day (day 21) of the induction phase (IP); the ABA content in E callus was over six times lower than in NE callus. In contrast, the IAA and GAs contents in primary explants of both genotypes in relation to ABA were low, but the contents of IAA and GAs exceeded that of ABA in the M9-10a tissues on the last day of IP. It is shown for the first time that endogenous ABA together with endogenous bioactive GAs and IAA is involved in acquisition of embryogenic competence in Medicago truncatula leaf somatic cells. These findings have a strong functional implication as they allow to improve the SE induction protocol.

Natural Auxin Does Not Inhibit Brefeldin A Induced PIN1 and PIN2 Internalization in Root Cells.

The vesicle trafficking inhibitor Brefeldin A (BFA) changes the localization of plasma membrane localized PINs, proteins that function as polar auxin efflux carriers, by inducing their accumulation within cells. Pretreatment with the synthetic auxin 1-NAA reduces this BFA-induced PIN internalization, suggesting that auxinic compounds inhibit the endocytosis of PIN proteins. However, the most important natural auxin, IAA, did not substantially inhibit PIN internalization unless a supplementary antioxidant, butylated hydroxytoluene (BHT), was also included in the incubation medium. We asked whether the relatively small inhibition caused by IAA alone could be explained by its instability in the incubation solution or whether IAA might interact with BHT to inhibit endocytosis. Analysis of the IAA concentration in the incubation solution and of DR5 reporter activity in the roots showed that IAA is both stable and active in the medium. Therefore, IAA degradation was not able to explain the inability of IAA to inhibit endocytosis. Furthermore, when applied in the absence of auxin, BHT caused a strong increase in the rate of PIN1 internalization and a weaker increase in the rate of PIN2 internalization. These increases were unaffected by the simultaneous application of IAA, further indicating that endocytosis is not inhibited by the natural auxin IAA under physiologically relevant conditions. Endocytosis was inhibited at the same rate with 2-NAA, an inactive auxin analog, as was observed with 1-NAA and more strongly than with natural auxins, supporting the idea that this inhibition is not auxin specific.

The integration of ACS2-generated ACC with GH3-mediated IAA homeostasis in NaCl-stressed primary root elongation of Arabidopsis seedlings

Plant root growth is controlled by auxin (IAA) and ethylene. The appropriate IAA concentration is regulated by many events, such as IAA biosynthesis, conjugation, and degradation. The levels of ethylene and its precursor 1-aminocyclopropane-1-carboxylic acid (ACC) depend on the activity of ACC synthases (ACSs). However, some questions have been raised: can ACS family members specifically regulate the ACC concentration in response to NaCl stress, and if so, how? How does ACC production affect IAA homeostasis during the root growth of Arabidopsis seedlings? Here, our observations showed that NaCl inhibition of root growth was greater in the ACS2-deficient mutants acs2-1 and acs2-2 because of the reduction of ACC and IAA accumulation in their root tips, while this reduction was rescued in transformants, including acs2 complementary (ACS2/acs2-1) and ACS2 overexpression (ACS2-OE) lines. The data showed that the decreased IAA levels resulted from increased activity of IAA conjugation enzymes, such as GH3.5 and GH3.9. These results suggest that ACS2 activity is an early response factor in the signaling pathway of NaCl-inhibited root growth.

Comparative evaluation of iodoacids removal by UV/persulfate and UV/H2O2 processes

To develop a cost-effective method for post-formation mitigation of iodinated disinfection by-products, degradation of iodoacids by UV, UV/PS (persulfate), and UV/H2O2 was extensively investigated in this study. UV direct photolysis of 4 iodoacids followed first-order kinetics with rate constants in the range of 2.43 × 10−4−3.02 × 10−3 cm2 kJ−1. The derived quantum yields (Ф254) of the 4 iodoacids range from 0.13 to 0.34, respectively. A quantitative structure-activity relationship (QSAR) model was subsequently established and applied to predict the direct photolysis rates of 6 other structurally similar iodoacids whose standards are commercially unavailable. At a UV dose of 140 mJ cm−2 which is typically applied for disinfection of drinking water, the removal percentages of 4 iodoacids were only between 3.35% and 34.7%. Thus, ICH2CO2H (IAA), the most photo-recalcitrant species, was selected as the target compound for removal in the UV/PS and UV/H2O2 processes. The IAA degradation rates decreased with increasing pH from 3 to 11 in both processes. Humic acid (HA) and HCO3− had inhibitory effects on IAA degradation in both processes. Cl− adversely affected the IAA degradation in the UV/PS process but had no effect in the UV/H2O2 process. Generally, in the deionized (DI) water, surface water, treated drinking water, and secondary effluent, UV/PS process is more effective than UV/H2O2 process for IAA removal, based on the same molar ratio of oxidant: IAA. SO4− generated in the UV/PS process yields a greater mineralization of IAA than HO in the UV/H2O2 process. IO3− was the predominant end-product in the UV/PS process, while I− was the major end-product in the UV/H2O2 process. The respective contributions of UV, HO, and SO4− for IAA removal in the UV/PS process were 7.8%, 14.7%, and 77.5%, respectively, at a specific condition (1.5 μM IAA, 60 μM oxidant, and pH 7). Compared to UV/H2O2 process, UV/PS was also observed as more cost-effective process based on the electrical energy per order (EE/O) and chemical cost.

A Synthetic Approach Reveals Extensive Tunability of Auxin Signaling

Explaining how the small molecule auxin triggers diverse yet specific responses is a long-standing challenge in plant biology. An essential step in auxin response is the degradation of Auxin/Indole-3-Acetic Acid (Aux/IAA, referred to hereafter as IAA) repressor proteins through interaction with auxin receptors. To systematically characterize diversity in degradation behaviors among IAA|receptor pairs, we engineered auxin-induced degradation of plant IAA proteins in yeast (Saccharomyces cerevisiae). We found that IAA degradation dynamics vary widely, depending on which receptor is present, and are not encoded solely by the degron-containing domain II. To facilitate this and future studies, we identified a mathematical model able to quantitatively describe IAA degradation behavior in a single parameter. Together, our results demonstrate the remarkable tunability conferred by specific configurations of the auxin response pathway.

Elevated indole-3-acetic acid peroxidase activity is involved in the cadmium-induced hydrogen peroxide production in barley root tip

All of the analyzed heavy metals significantly inhibited root growth, but in addition to Cd exposure an elevated IAA-POD activity was detected under Co, Cu and Hg treatment, while Ni and Pb inhibited its activity. The Cd-induced IAA-POD activity increased from the root apex towards to the mature region of root tips. However similar or even more severe root growth inhibition was observed by exogenously applied IAA, IAA-POD activity was activated only at high IAA concentrations. Elevated Cd-induced H2O2 production was detected both in the absence or in the presence of IAA in the reaction mixture, but in the case of IAA as a possible substrate for PODs the production of H2O2 increased markedly just in the Cd-treated roots. Exogenously applied H2O2 also activated IAA-POD activity. Our results indicated that in the development of Cd toxicity syndrome the production of ROS during IAA degradation by elevated IAA-POD activity plays a crucial role, mainly under severe Cd stress.

Evolutionary patterns in auxin action.

This review represents the first effort ever to survey the entire literature on auxin (indole-3-acetic acid, IAA) action in all plants, with special emphasis on the green plant lineage, including charophytes (the green alga group closest to the land plants), bryophytes (the most basal land plants), pteridophytes (vascular non-seed plants), and seed plants. What emerges from this survey is the surprising perspective that the physiological mechanisms for regulating IAA levels and many IAA-mediated responses found in seed plants are also present in charophytes and bryophytes, at least in nascent forms. For example, the available evidence suggests that the apical regions of both charophytes and liverworts synthesize IAA via a tryptophan-independent pathway, with IAA levels being regulated via the balance between the rates of IAA biosynthesis and IAA degradation. The apical regions of all the other land plants utilize the same class of biosynthetic pathway, but they have the potential to utilize IAA conjugation and conjugate hydrolysis reactions to achieve more precise spatial and temporal control of IAA levels. The thallus tips of charophytes exhibit saturable IAA influx and efflux carriers, which are apparently not sensitive to polar IAA transport inhibitors. By contrast, two divisions of bryophyte gametophytes and moss sporophytes are reported to carry out polar IAA transport, but these groups exhibit differing sensitivities to those inhibitors. Although the IAA regulation of charophyte development has received almost no research attention, the bryophytes manifest a wide range of developmental responses, including tropisms, apical dominance, and rhizoid initiation, which are subject to IAA regulation that resembles the hormonal control over corresponding responses in seed plants. In pteridophytes, IAA regulates root initiation and vascular tissue differentiation in a manner also very similar to its effects on those processes in seed plants. Thus, it is concluded that the seed plants did not evolve de novo mechanisms for mediating IAA responses, but have rather modified pre-existing mechanisms already operating in the early land plants. Finally, this paper discusses the encouraging prospects for investigating the molecular evolution of auxin action.

Hormonal and histological studies related to in vitro banana bud formation

Shoot apices of Musa subgroup AAA `Grande Naine' were used for in vitro culture establishment. The endogenous hormone levels and their effects on bud formation were evaluated during a 75-day period. Cytokinins, IAA and ABA were separated by HPLC and quantified by means of ELISA. Enzymatic degradation of IAA was determined by the colorimetric method. Explants were maintained on establishment medium for 60 days. The endogenous cytokinins were higher in the basal portion of the explant. Subculture to proliferation medium (65 to 75 days) resulted in a substantial increase of cytokinins in the basal portion and in a decline in the apical portion. 2iP was the predominant cytokinin in the tissue. The endogenous level of IAA and the IAA/cytokinin ratio decreased after the 65th day of culture. The level of ABA was reduced from the time of inoculation up to the 75th day of culture. Histological analysis indicated that buds formed at the leaf base at the 65th day of culture.

Identification of skatolyl hydroperoxide and its role in the peroxidase-catalysed oxidation of indol-3-yl acetic acid.

Indol-3-yl acetic acid (IAA, auxin) is a plant hormone whose degradation is a key determinant of plant growth and development. The first evidence for skatolyl hydroperoxide formation during the plant peroxidase-catalysed degradation of IAA has been obtained by electrospray MS. Skatolyl hydroperoxide degrades predominantly non-enzymically to oxindol-3-yl carbinol but in part enzymically into indol-3-yl methanol via a peroxidase cycle in which IAA acts as an electron donor. Skatolyl hydroperoxide is degradable by catalase. Horseradish peroxidase isoenzyme C (HRP-C) and anionic tobacco peroxidase (TOP) exhibit differences in their mechanisms of reaction. The insensitivity of the HRP-C-catalysed reaction to catalase is ascribed to the formation of HRP-C Compound III at the initiation step and its subsequent role in radical propagation. This is in contrast with the TOP-catalysed process in which skatolyl hydroperoxide has a key role. Indol-3-yl aldehyde is produced not via the peroxidase cycle but by catalysis involving ferrous peroxidase. Because indol-3-yl aldehyde is one of the main IAA-derived products identified in planta, we conclude that ferrous peroxidases participate in IAA catalytic transformations in vivo. A general scheme for peroxidase-catalysed IAA oxidation is presented.

IAA breakdown and its effect on auxin‐induced cell wall acidification in maize coleoptile segments

In excised Zea maus L. coleoptiles incubated in aerated media at high fresh weight per volume ratios, indole‐3‐acetic acid induces transient drops of extracellular pH. Based on the quantitative dependency of the response on the initial auxin concentration we developed a novel auxin bioassay, which allows reliable estimation of IAA concentrations between 10−85 and 10−5M. Using the bioassay and complementary concentration measurements by IAA fluorescence we found the transient IAA‐induced pH response paralleled by a decrease of auxin activity and concentration in the medium. This decline is rapid and starts immediately upon auxin addition, and insofar differs from the well known IAA degradation by epiphytic bacteria in long‐term auxin tests. We conclude that the transient character of the auxin pH response is due to rapid IAA metabolism. The effect occurs under those experimental conditions that are necessary for reliable estimations of auxin‐induced shifts of cell wall pH, which considerably complicates the interpretation of the results.

Development of phenolic compounds in maize anthers ( Zea mays) during cold pretreatment prior to androgenesis

Summary Androgenic capacity has been developed for some time in maize ( Zea mays L.) and cold pretreatment of anthers, e.g. for 14 days at 7°C, is considered necessary to induce androgenesis in this species. During this period, development of anther phenolic content and of IAA protection capacity of a phenolic extract were studied in three genotypes that respond differently to anther culture. Phenolic compounds were analyzed by HPLC and found to be mainly represented by six flavonol heterosides. Their levels were highly variable during the cold treatment, both between and within genotypes. These phenolics modified the in vitro degradation of IAA by IAA-oxidase. The extract from the most responsive genotype to androgenesis, DH5×DH7, gave maximal protection of IAA, whereas the ones from Seneca 60 and A188 (low-responsive and unresponsive, respectively) showed an IAA degradation capacity.

Peroxidase catalysed IAA Catabolism as one part of auxin regulation in Funaria hygrometrica

Summary The isoperoxidases of Funaria hygrometrica (Sibth.) wild type were analyzed in the phase of differentiation from chloronema to caulonema and compared with the mutant NAR-2. The mutant is not able to produce caulonema spontaneously; however, caulonema can be induced by exogenous auxin. Depending on the developmental stage, differences between the wild type (at the age of 8 and 14 days) and the mutant (at the age of 14 days) can be shown for isoenzyme patterns, and guaiacol-peroxidase and IAA-oxidaseperoxidase activities. In addition, cross reactions with 3 different polyclonal tobacco peroxidase antisera indicate that the degradation of free IAA in the mutant may be caused by basic IAA-oxidase-peroxxdasass acting in the cell wall during the process of polar auxin transport.

Kinetic properties of IAA oxidase from mung bean cotyledons

A crude enzyme preparation from mung bean cotyledons was separated into peroxidative and non-peroxidative IAA oxidase on a DEAE-cellulose column. Both fractions differed in their pH optima, K m and V max. The K m and V max of non-peroxidative IAA oxidase were higher than those of peroxidative IAA oxidase. Peroxidative IAA oxidase showed a linear increase in absorption at 247 and 254 nm after a short lag of 2–3 min. The addition of catalytic amounts of hydrogen peroxide eliminated the lag period and also enhanced the rate of IAA degradation. The non-peroxidative IAA oxidase fraction, however, did not exhibit any significant increase in absorption at 247 and 254 nm and showed a lag period of 5 min which was not affected by hydrogen peroxide. Instead, addition of the same catalytic amount of hydrogen peroxide inhibited the rate of IAA degradation. The peroxidative IAA oxidase fraction exhibited the reaction kinetics characteristic of peroxidase-catalysed IAA degradation. The rate of IAA oxidation by purified non-peroxidative IAA oxidase was very low. The slow rate of catalysis shown by non-peroxidative IAA oxidase appears to be due to the presence of inhibitor(s).

Effects of a short‐day treatment on pool size, synthesis, degradation and transport of 3‐indole‐acetic acid in Scots pine (Pinus sylvestris L.) seedlings

The effects of a short‐day treatment on pool‐size, synthesis, degradation, and transport of 3‐indole‐acetic acid (IAA) in Scots pine (Pinus sylvestris L.) seedlings were studied. The short‐day treatment decreased the pool of free IAA in the needles but did not significantly affect the pool‐sizes of free IAA in the shoot‐axis, hypocotyls, cotyledons and roots. The bound alkali‐hydrolysable IAA‐pools were not affected by the short‐day treatment. The synthesis and degradation of radioactive IAA were also unaffected by the short‐day treatment. The transport of radioactive IAA was greatest from needles to roots, and this transport was significantly decreased by the short‐day treatment.

Mode of action of glyphosate in relation to metabolism of indole‐3‐acetic acid

Studies were conducted with radio‐labeled indole‐3‐acetic acid ([2‐14C] IAA) and tobacco callus culture (Nicotiana tabacum L. cv. White Gold) to investigate the mode of action of the herbicide glyphosate (N‐phosphonomethylglycine). The tissue was first grown with or without glyphosate for 1 to 14 days and then incubated with [2‐14C] IAA for 4 h. Metabolism of [2‐14C] IAA in the tissue was studies by solvent fractionation, high performance liquid chromatography and liquid scintillation counting. The tissue grown with 0.2 mM glyphosate had low level of free [2‐14C] IAA and high levels of other fractions containing metabolites and conjugates of the labeled IAA. After 1 day of glyphosate treatment the free [2‐14C] IAA level in the tissue was reduced by 77% compared to that of the control; after 10 days of treatment the decrease was 96%. The decrease in the free [2‐14C] IAA level was not due to inhibition of IAA uptake, but due to enhanced rates of oxidation and conjugate formation of IAA. The increased oxidation of IAA in the treated tissue was not due to a direct effect of glyphosate on IAA‐oxidase since glyphosate was inactive on IAA oxidation in a cell‐free system in vitro. The glyphosate‐induced growth inhibition was partially overcome by addition of 1 μM 2,4‐dichlorophenoxyacetic acid to the medium. The results lead to the conclusion that glyphosate inhibits growth by depletion of free IAA through rapid acceleration of both conjugate formation and oxidative degradation of IAA.

Absorption and Metabolism of Radioactive Auxins in the Induced Rice Callus

During callus induction, auxin uptake and metabolism in rice seeds were investigated with 14C-carboxyl-labelled 2, 4-D and IAA. The uptake and metabolism in rice callus were compared with tobacco and barnyardgrass callus cultures. Radioactivity of 2, 4-D absorbed in the callus cultures and rice seeds was high in the 80% ethanol fraction and low in the residual fraction but scarce in the gas phase, expected to contain CO2 owing to the decarboxylation. Two kinds of 2, 4-D metabolites were present in the 80% ethanol fraction extracted from rice seedlings, rice callus and barnyardgrass callus. Inhibitory activities of them were lower than that of 2, 4-D in the growth test with rice seedlings. It seems that they are different from 2, 4-D-aspartic acid on the base of Rf value of chromatogram. From the quantitative research on 2, 4-D and 2, 4-D metabolites, it was shown that the tissues inducing callus contained higher level of 2, 4-D than those which had not induced callus. The barnyardgrass, which had required high concentrations of 2, 4-D for callus induction, contained high level of 2, 4-D metabolites but low level of 2, 4-D, when compared with rice callus. Therefore, it is assumcd that 2, 4-D level plays an important role in callus induction on the tissues. In ricc callus, most of IAA was converted to IAA-aspartic acid or degraded into CO2. Requirement of high concentration of IAA in rice callus for callus induction and subculture seems to be caused by faster degradation and inactivation of IAA than those of 2, 4-D. It is probable that 2, 4-D directly acts to the callus induction but not via IAA production by 2, 4-D, because the level of IAA, which would be required for callus induction, was not found in the 2, 4-D treated rice tissues. And also, selectivity of 2, 4-D as a herbicide is dis-cussed here in the relation to 2, 4-D metabolism in plants.

Effects of orchinol and related phenanthrenes on the enzymic degradation of indole-3-acetic acid

Orchinol, hircinol, loroglossol and certain related phenanthrenes inhibited horseradish peroxidase-catalysed IAA degradation to a varied degree. Among

The Interaction of Benzoic Acid with IAA Transport and Degradation in Plants, with Special Reference to Nectria galligena Cankers in Apples

The Interaction of Benzoic Acid with IAA Transport and Degradation in Plants, with Special Reference to Nectria galligena Cankers in Apples