Regulation of IAA-Metabolizing Enzymes in Plants by an Anti-auxin, 3-(4-Phellylcarbostyriloxy)acetic Acid

A viridicatin derivative having anti-auxin action, i.e. 3-(4-phenylcarbostyriloxy)acetic acid (V-OCH₂COOH) was found to increase the formation of both IAA (indole-3-acetic acid)-oxidase and -synthetase in rice and pea seedlings. With the IAA synthetase, the activity on indolepyruvic acid was markedly increased. V-OCH₂COOH stimulated the induction ofIAA oxidase in the excised segments from pea epicotyl, but did not IAA synthetase. The effect of V-OCH₂COOH on the former was inhibited by cycloheximide. Activity of the IAA oxidase extracted from pea epicotyl and dialyzed was also stimulated by V-OCH₂COOH in the presence of a cofactor such as 2,4-dichlorophenol. Effect of IAA per se on enzyme regulation was tested in parallel and discussed.     

Physiological activity of a viridicatin derivative, 3-(4-phenylcarbostyriloxy) acetic acid

A carboxymethylene derivative (V-OCH₂COOH) of viridicatin (V-OH)promoted the root growth of rice and sesame seedlings. V-OCH₂COOHhad no known hormonal activities, per se, but did have an inhibitoryeffect on IAA and 2,4-D-induced growth of Avena coleoptile sectionsand of carrot root callus. However, inhibition by VOCH2COOHof 2,4-D-induced growth in carrot root callus was to some extentreversed by increasing the concentration of 2,4-D. V-OCH₂C0OHseemed to competitively inhibit IAA-induced elongation of Avenacoleoptile sections. (Received September 14, 1970; )     

悉生培养微缩体系食细菌线虫提高土壤激素含量的机制

研究土壤食细菌线虫与细菌的相互作用及其生态功能是土壤生态学的核心内容之一。食细菌线虫取食细菌可以促进土壤中氮素的矿化,提高氮素养分的供给,改善土壤的营养条件,从而促进植物的生长发育。土壤食细菌线虫促进植物根系生长的"养分作用机制"已得到确认,而"激素作用机制"还存在争议。从供试土壤中筛选获得一株高效产IAA细菌和两种不同cp值的食细菌线虫,通过设置简化的悉生培养系统,对这两种土著食细菌线虫与土著产IAA细菌之间的相互作用,及其对土壤中IAA含量变化的影响进行研究。结果表明:两种食细菌线虫的取食均能促进细菌数量和活性的增强,食细菌线虫与产IAA细菌相互作用也能显著增加土壤中IAA的含量;这些促进作用受到接种食细菌线虫的种类以及培养时间的影响:在培养第10天和第20天时,接种cp值为1的中杆属食细菌线虫显著增加了产IAA细菌的数量;在培养第10天和第30天时,相比较接种cp值为2的头叶属食细菌线虫,接种中杆属食细菌线虫显著提高了土壤中IAA的含量。     

A morphogenetic role for ethylene in hypocotyl cultures of Digitalis obscura L.

The effect of exogenously applied ethylene on organogenesis in Digitalis obscura L. hypocotyls cultured in vitro was studied. Interactions of this gas with other growth regulators was also tested. Ethylene by itself only promoted root formation. Shoot regeneration was obtained in presence of indoleacetic acid and kinetin. The addition of ethylene (10 ppm) increased the caulogenetic action of this medium; higher concentrations than 10 ppm reduced this response. Kinetin alone did not promote organogenesis and nullified the promotive effect of ethylene on rhizogenesis.Abbreviations BM basal medium - IAA indoleacetic acid - Kn kinetin     

The in vitro Germination of Pollen of Setaria sphacelata

The effects of various substances upon germination and tube growth of pollen of Setaria sphacelata were investigated in hanging-drop culture. Both sucrose (0.6–0.7 M) and boron (1–5 ppm, as borate) are essential for germination. Comparable results were obtained with boric acid, sodium tetraborate and tri-n-butyl borate as boron sources, but sodium tetraphenylboron was inhibitory. Good germination and growth were obtained with raffinose and cellobiose, alone or in combination with sucrose (total 0.5 M); 0.25 M rhamnose, lactose and glycerol were without effect, and xylose, galactose and glucose were slightly inhibitory in the presence of 0.25 M sucrose; 0.25 M arabinose, fructose, mannose, sorbose, maltose, mannitol and sorbitol completely inhibited germination, even in the presence of 0.25 M sucrose. IAA and GA (0.01–10 ppm) could not replace or supplement the effects of borate on germination and growth, indicating the pollen to be self-sufficient in this respect. Riboflavin (0.1–10 ppm) and calcium pantothenate (1–100 ppm) stimulated germination and growth, whereas 0.01–10 ppm of thiamine, pyridoxine, nicotinic acid and ascorbic acid were generally without effect. Although copper sulphate, manganese sulphate, zinc sulphate and ammonium molybdate could not replace boric acid, 1.0 ppm of copper, manganese and zinc stimulated germination and growth in the presence of boron. In no instance were tubes found comparable in length to those required for fertilisation in vivo. It was concluded that the pollen probably requires a complex mixture of substances, including sucrose and borate, before this can be achieved in vitro.     

Role of auxin and gibberellin in differentiation of primary Phloem fibers

The hypothesis that auxin and gibberellic acid (GA₃) control the differentiation of primary phloem fibers is confirmed for the stem of Coleus blumei Benth. Indoleacetic acid (IAA) alone sufficed to cause the differentiation of a few primary phloem fibers. In long term experiments auxin induced a considerable number of fibers in mature internodes. GA₃ by itself did not exert any effect on fiber differentiation. Combinatiosn of IAA with GA₃ completely replaced the role of the leaves in primary phloem fiber differentiation qualitatively and quantitatively. Although the combined effect of the two growth hormones diminished considerably with increasing distance from the source of induction, auxin with GA₃ or IAA alone induced fibers in a few internodes below the application site. When various combinations of both hormones were applied, high concentrations of IAA stimulated rapid differentiation of fibers with thick secondary walls, while high levels of GA₃ resulted in long fibers with thin walls. The size of the primary phloem fibers correlated with the dimensions of the differentiating internode, thereby providing evidence that both growth regulators figure in the control of stem extension. High IAA/low GA₃ concentrations have an inhibitory effect on internode elongation, whereas low IAA/high GA₃ concentrations promote maximal stem elongation.     

The Auxins IAA and 4-Cl-IAA Differentially Modify Gibberellin Action via Ethylene Response in Developing Pea Fruit

This study explores the unique growth-regulatory roles of two naturally occurring auxins, indole-3-acetic acid (IAA) and 4-chloroindole-3-acetic acid (4-Cl-IAA), and their interactions with gibberellin (GA) during early pea (Pisum sativum L.) fruit development. We have previously shown that 4-Cl-IAA can replace the seed requirement in pea pericarp growth (length and fresh weight), whereas IAA had no effect or was inhibitory. When applied simultaneously, gibberellin (GA₃ or GA₁) and 4-Cl-IAA had a synergistic effect on pericarp growth. In the present study, we found that simultaneous application of IAA and GA₃ to deseeded pericarps inhibited GA₃-stimulated growth. The inhibitory effect of IAA on GA-stimulated growth was mimicked by treatment with ethephon (ethylene releasing agent), and the inhibitory effects of IAA and ethylene on GA-mediated growth were reversed by silver thiosulfate (STS), an ethylene action inhibitor. Although pretreatment with STS could retard senescence of IAA-treated pericarps, STS pretreatment did not lead to IAA-induced pericarp growth. Although 4-Cl-IAA stimulated growth whereas IAA was ineffective, both auxins induced similar levels of ethylene evolution. However, only 4-Cl-IAA-stimulated growth was insensitive to the effects of ethylene. Gibberellin treatment did not influence the amount of ethylene released from pericarps in the presence or absence of either auxin. We propose a growth regulatory role for 4-Cl-IAA through induction of GA biosynthesis and inhibition of ethylene action. Additionally, ethylene (IAA-induced or IAA-independent) may inhibit GA responses under physiological conditions that limit fruit growth.     

Stimulation of Plant Growth and Drought Tolerance by Native Microorganisms (AM Fungi and Bacteria) from Dry Environments: Mechanisms Related to Bacterial Effectiveness

In this study we tested whether rhizosphere microorganisms can increase drought tolerance to plants growing under water-limitation conditions. Three indigenous bacterial strains isolated from droughted soil and identified as Pseudomonas putida, Pseudomonas sp., and Bacillus megaterium were able to stimulate plant growth under dry conditions. When the bacteria were grown in axenic culture at increasing osmotic stress caused by polyethylene glycol (PEG) levels (from 0 to 60%) they showed osmotic tolerance and only Pseudomonas sp. decreased indol acetic acid (IAA) production concomitantly with an increase of osmotic stress (PEG) in the medium. P. putida and B. megaterium exhibited the highest osmotic tolerance and both strains also showed increased proline content, involved in osmotic cellular adaptation, as much as increased osmotic stress caused by NaCl supply. These bacteria seem to have developed mechanisms to cope with drought stress. The increase in IAA production by P. putida and B. megaterium at a PEG concentration of 60% is an indication of bacterial resistance to drought. Their inoculation increased shoot and root biomass and water content under drought conditions. Bacterial IAA production under stressed conditions may explain their effectiveness in promoting plant growth and shoot water content increasing plant drought tolerance. B. megaterium was the most efficient bacteria under drought (in successive harvests) either applied alone or associated with the autochthonous arbuscular mycorrhizal fungi Glomus coronatum, Glomus constrictum or Glomus claroideum. B. megaterium colonized the rhizosphere and endorhizosphere zone. We can say, therefore, that microbial activities of adapted strains represent a positive effect on plant development under drought conditions.     

Screening and Optimization of Indole-3-Acetic Acid Production and Phosphate Solubilization from Rhizobacteria Aimed at Improving Plant Growth

A total of 216 bacterial strains were isolated from rice rhizospheric soils in Northern Thailand. The bacterial strains were initially tested for solubilization of inorganic phosphate, indole acetic acid (IAA) production, selected strains were then tested for optimized conditions for IAA production and whether these caused stimulatory effects on bean and maize seedling growth. It was found that all strains had solubilized inorganic phosphate (P), but only 18.05% produced IAA. The best IAA producer was identified by biochemical testing and 16S rDNA sequence analysis as Klebsiella SN 1.1. In addition to being the best IAA producer, this strain was a high P-solubilizer and produced the highest amount of IAA (291.97 ± 0.19 ppm) in culture media supplemented with l-tryptophan. The maximum production of IAA was achieved after 9 days of incubation. The culture requirements were optimized for maximum IAA production. The tested of IAA production by selected isolates was studied in a medium with 0, 0.1, 0.2, 0.5, 0.7, and 0.9% (v/v) l-tryptophan. Low levels (12.6 ppm) of IAA production was recorded without tryptophan addition. Production of IAA in Klebsiella SN 1.1 increased with an increase to 0.2% (v/v) tryptophan concentration. The production of IAA was further confirmed by extraction of crude IAA from this isolate and subsequent Thin Layer Chromatography (TLC) analysis. A specific spot from the extracted IAA production was found to correspond with a standard spot of IAA with the same R _f value. The Klebsiella strain SN 1.1 also demonstrated stimulatory effects on bean seedlings in vivo.     

Involvement of IAA in the interaction betweenAzospirillum brasilense andPanicum miliaceum roots

The possible involvement of IAA in the effect thatAzospirillum brasilense has on the elongation and morphology ofPanicum miliaceum roots was examined by comparing in a Petri dish system the effects of inoculation with a wild strain (Cd) with those of an IAA-overproducing mutant (FT-326). Both bacterial strains produced IAA in culture in the absence of tryptophan. At the stationary growth phase, production of IAA by FT-326 wasca. 12 times greater than that of Cd. When inoculation was made with bacterial concentrations higher than, 10⁶ colony forming units ml^–1 (CFU ml^–1), both strains inhibited root elongation to the same extent. At lower concentrations Cd enhanced elongation, by 15–20%, while FT-326 was ineffective. Both strains promoted root-hair development, and root-hairs were produced nearer the root tip the higher the bacterial concentration (e. g. root elongation region was reduced). Effects of FT-326 on root-hair development were greater than those of Cd. Acidified ether extracts of Cd and FT-326 cultures had inhibitory or promoting effects on root elongation depending on the dilution applied. At low dilutions, extracts from FT-326 were more inhibitory for elongation than those from Cd. At higher dilutions root elongation was promoted, but FT-326 extracts had to be more diluted than those from Cd. Dilutions that promoted root elongation contained supra-optimal concentrations of IAA, 1–3 orders of magnitude higher than those required for optimal enhancement by synthetic IAA. It is suggested that the bacteria produce in culture an IAA-antagonist or growth inhibitor that decreases the effectiveness of IAA action. The large variability reported for the effects ofAzospirillum on root elongation could be the result of the opposite effects on root elongation of IAA and other compounds, produced by the bacteria.     

Hormonal regulation of cotton ovule and fiber growth: Effects of bromodeoxyuridine,AMO-1618 and p-chlorophenoxyisobutyric acid

The effects of 5-bromo-2-deoxyuridine (BUdR, thymidine analogue), AMO-1618 (2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine carboxylate methyl chloride), a growth retardant, and p-chlorophenoxyisobutyric acid (PCIB, an antiauxin) on growth (dry weight increase) and fiber development in unfertilized cotton (Gossypium hirsutum L.) ovules grown in vitro have been studied. BUdR (5 M) causes about 70% inhibition of fiber production, with little effect on ovule growth, if applied during the first 6 d of culture in the presence of GA₃ and IAA. AMO-1618, when used with GA₃ alone, causes only a small reduction in both dry weight and fiber production, but when used with IAA alone reduces both fiber production and dry weight, the effect on the latter being predominant. In the presence of both IAA and GA₃, AMO-1618 causes a small decrease in fiber production but a major decrease in dry weight. PCIB completely inhibits fiber growth but has little effect on dry weight, especially when GA₃ is present. These results indicate that GA₃ mainly promotes ovule growth while IAA is largerly responsible for fiber growth.Abbreviations AMO-1618 2-isopropyl-4-dimethylamino-5-methylphenyl-1-piperidine carboxylate methyl chloride - BUdR 5-bromo-2-deoxyuridine - GA₃ gibberellic acid - IAA indole-3-acetic acid - PCIB p-chlorophenoxyisobutyric acid - TFU total fiber units     

Effect of plant growth substances on the growth of axillary buds in cultured stem segments of Phaseolus vulgaris L.

The hormonal control of axillary bud growth was investigated in cultured stem segments of Phaseolus vulgaris L. When the stem explants were excised and implanted with their apical end in a solid nutrient medium, outgrowth of the axillary buds-located at the midline of the segment-was induced. However, if indoleacetic acid (IAA) or naphthaleneacetic acid (NAA) was included in the medium, bud growth was inhibited. The exposure of the apical end to IAA also caused bud abscission and prevented the appearance of new lateral buds.In contrast to apically inserted segments, those implanted in the control medium with their basal end showed much less bud growth. In these segments, the auxin added to the medium either had no effect or caused a slight stimulation of bud growth.The IAA transport inhibitor N-1-naphthylphthalamic acid (NPA) relieved bud growth inhibition by IAA. This suggests that the effect of IAA applied at the apical end requires the transport of IAA itself rather than a second factor. With the apical end of the segment inserted into the IAA-containing medium, simultaneous basal application of IAA relieved to some extent the inhibitory effect of the apical IAA treatment. These results, together with data presented in a related article [Lim R and Tamas I (1989) Plant Growth Regul 8: 151–164], show that the polarity of IAA transport is a critical factor in the control of axillary bud growth.Of the IAA conjugates tested for their effect on axillary bud growth, indoleacetyl alanine, indoleacetic acid ethyl ester, indoleacetyl-myo-inositol and indoleacetyl glucopyranose were strongly inhibitory when they were applied to the apical end of the stem explants. There was a modest reduction of growth by indoleacetyl glycine and indoleacetyl phenylalanine. Indoleacetyl aspartic acid and indoleglyoxylic acid had no effect.In addition to IAA and its conjugates, a number of other plant growth substances also affected axillary bud growth when applied to the apical end of stem segments. Myo-inositol caused some increase in the rate of growth, but it slightly enhanced the inhibitory effect of IAA when the two substances were added together. Gibberellic acid (GA₃) caused some stimulation of bud growth when the explants were from younger, rather than older plants. The presence of abscisic acid (ABA) in the medium had no effect on axillary bud growth. Both kinetin and zeatin caused some inhibition of axillary buds from younger plants but had the opposite effect on buds from older ones. Kinetin also enhanced the inhibitory effect of IAA when the two were applied together.In conclusion, axillary buds of cultured stem segments showed great sensitivity to auxins and certain other substances. Their growth responded to polarity effects and the interaction among different substances. Therefore, the use of cultured stem segments seems to offer a convenient, sensitive and versatile test system for the study of axillary bud growth regulation.     

Inhibition of Lettuce Seed Germination and Root Elongation by Derivatives of Auxin and Reversal by Derivatives of Cycocel

Lettuce seed germination or lettuce root elongation after germination in water was inhibited by 5.7 × 10^-6M indoleacetic acid (IAA) and designated other IAA derivatives. These IAA-inhibited growth responses were reversed by 10^-5 to 10^-6M Cycocel, (2-chloroethyl) trimethylammonium chloride, which alone was without effect. Only those Cycocel analogs, which have previously been shown to be active as plant growth retardants, were effective in reversing IAA inhibition of germination or root elongation. These results are consistent with the concept that Cycocel at low concentrations acts as an auxin antagonist. However. Cycocel did not reverse the inhibitory effects from indole-3-propionic acid or indole-3-butyric acid.     

Studies on the root nodules of leguminous plants: The production of indole acetic acid in culture by a Rhizobium sp. from a leguminous climbing shrub Derris scandens benth

The Rhizobium sp. When isolated form the root nodules of a leguminous climbing shrub Derris scandens produced a high amount of indole acetic acid (IAA) (135.2 μg/ml) from the tryptophan-supple-mented basal medium. Growth and IAA production started simultaneously, and the maximum amount of IAA was produced as a secondary metabolite in the stationary phase of growth. The IAA production by the Rhizobium sp. was increased by 503% when the medium was supplemented with mannitol (2%), KNO₃ (0.2%), nicotinic acid (0.1 μg/ml) and MnSO₄ (1 μg/ml) in addition to tryptophan (4 mg/ml)/ The possible role of the rhizobial production of IAA on the rhizobia-legume symbiosis is also discussed.     

Involvement of phytohormones in the development of interaction between wheat seedlings and endophytic <Emphasis Type="Italic">Bacillus subtilis</Emphasis> strain 11BM

Wheat (Triticum aestivum L., cv. Kazakhstanskaya 10) seedling growth activation by the endophytic 11BM strain of the bacterium Bacillus subtilis Cohn and the involvement of phytohormones in this process were studied. At the concentration used, bacteria enhanced wheat root and shoot growth as compared to control. Biotests demonstrated auxin-, cytokinin-, and gibberellin-like activities of the endophyte, but the result depended on the way of experiment performing. When wheat seeds were treated with the spores of B. subtilis 11BM strain, the concentrations of IAA and ABA increased transiently in the roots and shoots of the seedlings. The involvement of IAA oxidase in the plant response to inoculation with bacteria was shown; it was accompanied by a decrease in enzyme activity, which occurred later than auxin accumulation. It was concluded that observed changes in the hormonal status of wheat plants under the influence of the endophytic bacterial strain may be one of the mechanisms for seedling growth stimulation.     

一株促生秸秆降解菌的分离与鉴定

针对秸秆处理不当影响全世界环境污染的问题，筛选多功能秸秆降解菌，旨在得到高效降解秸秆且具有促生作用的微生物菌种。结合纤维素钠-刚果红(CMC-Na)平板筛选，通过16S rRNA基因分析，进行菌株鉴定，得到一株具有纤维素降解效果的菌株XJ-132,经16S rRNA基因鉴定为枯草芽胞杆菌(Bacillus subtilis)。与单独施用秸秆处理相比，加入菌株XJ-132 60 d后，秸秆降解率提高21.0%,且对水稻生长促进作用显著，地上、下部鲜重分别增加17.8%和9.6%。水稻种子喷施菌株XJ-132发酵液，低浓度发酵液对种子萌发具有一定促进作用。结果表明，菌株XJ-132可能通过产吲哚乙酸(IAA)、产铁载体、产氨等多种有益物质，降解秸秆的同时促进水稻生长。筛选具有促生作用的秸秆降解菌能够更好地加速秸秆降解，具有广泛的开发利用前景。     

Fluoride‐sensitivity of growth and acid production of oral Actinomyces: comparison with oral Streptococcus

Actinomyces are predominant oral bacteria; however, their cariogenic potential in terms of acid production and fluoride sensitivity has not been elucidated in detail and compared with that of other caries‐associated oral bacteria, such as Streptococcus. Therefore, this study aimed to elucidate and compare the acid production and growth of Actinomyces and Streptococcus in the presence of bicarbonate and fluoride to mimic conditions in the oral cavity. Acid production from glucose was measured by pH‐stat at pH 5.5 and 7.0 under anaerobic conditions. Growth rate was assessed by optical density in anaerobic culture. Although Actinomyces produced acid at a lower rate than did Streptococcus, their acid production was more tolerant of fluoride (ID_{acid production} 50 = 110–170 ppm at pH 7.0 and 10–13 ppm at pH 5.5) than that of Streptococcus (ID_{acid production} 50 = 36–53 ppm at pH 7.0 and 6.3–6.5 ppm at pH 5.5). Bicarbonate increased acid production by Actinomyces with prominent succinate production and enhanced their fluoride tolerance (ID_{acid production} 50 = 220–320 ppm at pH 7.0 and 33–52 ppm at pH 5.5). Bicarbonate had no effect on these variables in Streptococcus. In addition, although the growth rate of Actinomyces was lower than that of Streptococcus, Actinomyces growth was more tolerant of fluoride (ID_growth 50 = 130–160 ppm) than was that of Streptococcus (ID_growth 50 = 27–36 ppm). These results indicate that oral Actinomyces are more tolerant of fluoride than oral Streptococcus, and bicarbonate enhances the fluoride tolerance of oral Actinomyces. Because of the limited number of species tested here, further study is needed to generalize these findings to the genus level.     

Relations polyphenols-croissance: Lignification et limitation de croissance chez Lycopersicum esculentum

Abstract Polyphenols and growth – Lignification and limitation of growth in Lycopersicum esculentum. When fed with quinic acid, young tomato seedlings (Lycopersicum esculentum Mill. cv. St. Pierre) exhibited reduced growth and marked changes in cell wall composition: cellulose concentrations decreased whereas those of lignin increased. Exogenously supplied growth substances (IAA, GA₃) affected both the size of the plants and the lignification process: IAA treatments resembled quinic acid induced modifications with regard to both size and lignification: GA₃ applied to quinate treated plants counteracted the effects of this compound by reducing the lignin content and improving the growth. The possible effect of abnormal lignification as a limiting factor in cell growth is supported by the characterization of lignins in tissues different from xylem.     

Activity of Various Growth Substances in the Avena First Internode Test

The elongation growth of the Avena first internode segments was studied in the presence of one or several of the following growth substances: indoleacetic acid (IAA), 6-fur-furylamino purine (FAP, kinetin), 6-benzylamino purine (BAP), gibberellin A₃ (GA₃) and A₄₊₇ (GA₄₊₇), and abscisic acid (ABA). The cytokinins at concentrations of 10^?7 to 10^?6M stimulated growth with 4 to 6 per cent but this effect was not statistically significant. Concentrations higher than 5 × 10^?6M inhibited growth. FAP and BAP (from 10^?8M to 10^?6M) had no significant interaction with any other growth substance used. The two-factor interactions of IAA × ABA, IAA × GA₃, and GA₃× ABA, as well as the three-factor interaction IAA × ABA × GA₃ were significant. However, the IAA × ABA interaction was significant only when high concentration (10^?6M) of ABA was used. The growth inhibition produced by 10^?7 and 10^?6M ABA was overcome by about equimolar concentrations of IAA. The stimulation of growth by GA₃ and GA₄₊₇ (10^?9 to 10^?7M) was prevented by simultaneous application of ABA, and it was reduced significantly by application of IAA (10^?7 to 10^?8M). GA3 at 10^?8M combined with different concentrations of IAA gave slightly higher elongation than IAA alone but the observed values were significantly lower than expected assuming independent additive action.     

Impact of acetaldehyde- and pyruvic acid-bound sulphur dioxide on wine lactic acid bacteria

Aims: To investigate the impact of acetaldehyde‐ and pyruvic acid‐bound sulphur dioxide on wine lactic acid bacteria (LAB). Methods and Results: Growth studies were performed where Oenococcus oeni, Pediococcus parvulus, Ped. damnosus and Lactobacillus hilgardii were inoculated into media containing various concentrations of acetaldehyde or pyruvic acid and an equimolar concentration of SO₂ at pH 3·50 and 3·70. Low concentrations of acetaldehyde‐ and pyruvic acid‐bound SO₂ were inhibitory to the growth of all bacteria although acetaldehyde‐bound SO₂ was generally more inhibitory than pyruvic acid‐bound SO₂. Inhibition was greater at pH 3·50 than 3·70, and Lact. hilgardii was the most sensitive to acetaldehyde‐bound SO₂, while O. oeni was the most sensitive to pyruvic acid‐bound SO₂. Degradation of SO₂‐bound acetaldehyde was observed for all LAB, and aside from O. oeni, there was also complete degradation of SO₂‐bound pyruvic acid at both pH values. O. oeni only degraded pyruvic acid at pH 3·70. Degradation of SO₂‐bound acetaldehyde or pyruvic acid did not correlate with bacterial growth as inhibition was always observed in media containing bound SO₂. Conclusions: Acetaldehyde‐ and pyruvic acid‐bound SO₂ were inhibitory to wine LAB growth at concentrations as low as 5 mg l^?1. Despite this inhibition, all wine LAB degraded SO₂‐bound acetaldehyde and pyruvic acid suggesting that bound SO₂ may have a bacteriostatic rather than bacteriocidal action. Significance and Impact of the Study: Sulphur dioxide bound to acetaldehyde or pyruvic acid is inhibitory to growth of wine LAB and must be considered when conducting the malolactic fermentation or controlling the growth of spoilage bacteria such as Pediococcus and Lactobacillus.