The effect of light on the production of ethylene from 1-aminocyclopropane-1-carboxylic acid by leaves

White light inhibits the conversion of 1-amino-cyclopropane-1-carboxylic acid (ACC) in discs of green leaves of tobacco (Nicotiana tabacum L.) and segments of oat (Avena sativa L.) leaves by from 60 to 90%. Etiolated oat leaves do not show this effect. The general nature of the effect is shown by its presence in both a mono- and a dicotyledon. Since the leaves have been grown and pre-incubated in light, yet can produce from 2 to 9 times as much ethylene in the dark as in the light, it follows that the light inhibition is fully reversible. The inhibition by light is about equal to that exerted in the dark by CoCl₂; it can be partly reversed by dithiothreitol and completely by mercaptoethanol. Thus the light is probably acting, via the photosynthetic system, on the SH group(s) of the enzyme system converting ACC to ethylene.Abbreviation ACC 1-aminocyclopropane-1-carboxylic acid     

Accumulation of 1-(malonylamino)cyclopropane-1-carboxylic acid in ethylene-synthesizing tobacco leaves

During the hypersensitive reaction of Samsun NN tobacco to tobacco mosaic virus (TMV) the inoculated leaves synthesize large quantities of ethylene. At the same time, 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), a conjugate of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) accumulates. Smaller amounts of MACC are formed concomitant with ethylene synthesis during the normal development of tobacco leaves. The conjugate appears neither to be hydrolysed to liberate ACC, nor to be transported to other plant parts. Its accumulation thus reflects the history of the operation of the pathway of ethylene synthesis in the leaf. In floating leaf discs exogenously applied ACC was converted only slowly to both ethylene and MACC. More ethylene and less MACC were produced in darkness than in light, suggesting that environmental conditions may influence the ratio at which ACC in converted to either ethylene or MACC.     

Light inhibition of the conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene in leaves is mediated through carbon dioxide

The mechanism of light-inhibited ethylene production in excised rice (Oryza sativa L.) and tobacco (Nicotiana tabacum L.) leaves was examined. In segments of rice leaves light substantially inhibited the endogenous ethylene production, but when CO₂ was added into the incubation flask, the rate of endogenous ethylene production in the light increased markedly, to a level which was even higher than that produced in the dark. Carbon dioxide, however, had no appreciable effect of leaf segments incubated in the dark. The endogenous level of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, was not significantly affected by lightdark or CO₂ treatment, indicating that dark treatment or CO₂exerted its effect by promoting the conversion of ACC to ethylene. This conclusion was supported by the observations that the rate of conversion of exogenously applied ACC to ethylene was similarly inhibited by light, and this inhibition was relieved in the presence of CO₂. Similar results were obtained with tobacco leaf discs. The concentrations of CO₂ giving half-maximal activity was about 0.06%, which was only slightly above the ambient level of 0.03%. The modulation of ACC conversion to ethylene by CO₂ or light in detached leaves of both rice and tobacco was rapid and fully reversible, indicating that CO₂ regulates the activity, but not the synthesis, of the enzyme converting ACC to ethylene. Our results indicate that light inhibition of ethylene production in detached leaves is mediated through the internal level of CO₂, which directly modulates the activity of the enzyme converting ACC to ethylene.Abbreviation ACC 1-aminocyclopropane-1-carboxylic acid Recipient of a Republic of China National Science Council Fellowship     

The effect of plant-hormone pretreatments on ethylene production and synthesis of 1-aminocyclopropane-1-carboxylic acid in water-stressed wheat leaves

Excised wheat (Triticum aestivum L.) leaves, when subjected to drought stress, increased ethylene production as a result of an increased synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) and an increased activity of the ethyleneforming enzyme (EFE), which catalyzes the conversion of ACC to ethylene. The rise in EFE activity was maximal within 2 h after the stress period, while rehydration to relieve water stress reduced EFE activity within 3 h to levels similar to those in nonstressed tissue. Pretreatment of the leaves with benzyladenine or indole-3-acetic acid prior to water stress caused further increase in ethylene production and in endogenous ACC level. Conversely, pretreatment of wheat leaves with abscisic acid reduced ethylene production to levels produced by nonstressed leaves; this reduction in ethylene production was accompanied by a decrease in ACC content. However, none of these hormone pretreatments significantly affected the EFE level in stressed or nonstressed leaves. These data indicate that the plant hormones participate in regulation of water-stress ethylene production primarily by modulating the level of ACC.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - BA N⁶-benzyladenine - EFE ethylene-forming enzyme - IAA indole-3-acetic acid     

Stimulation of ethylene production in detached rice leaves by vanadate

The effect of vanadate on ethylene biosynthesis in detached rice leaves was investigated. Vanadate at pH 5.0–7.0 effectively enhanced ethylene production within 3 h of its application. It promoted the conversion of ACC to ethylene. Treatment with vanadate did not decrease ACC level until late stage of incubation, i.e. at 12 h after incubation. Molybdate, an inhibitor of phosphatase had no or much less stimulatory effect on ethylene production than did vanadate at comparable concentrations. Azide, an inhibitor of F₁-ATPase, inhibited ethylene production in detached rice leaves. FC and vanadate were observed to be synergisticly increased ethylene production in detached rice leaves. In conclusion, plasma membrane H⁺-ATPase does not seem to be involved in ethylene biosynthesis in detached rice leaves.Abbreviations ACC 1-Aminocyclopropane-1-carboxylic acid - FC Fusicoccin     

Wound-induced Ethylene Formation in Albedo Tissue of Citrus Fruit

Excised albedo tissue of citrus fruit (Citrus unshiu and Citrus hassaku) produced ethylene at an increasing rate in response to wounding and aging. The application of 1-aminocyclopropane-1-carboxylic acid (ACC) enhanced ethylene production in both the fresh and aged tissues, but this increase was greater in the aged tissue than in the fresh tissue. ACC content was very low in fresh tissue but increased greatly in aging tissue, paralleling the rise in ethylene production. Aminoethoxyvinylglycine (AVG) strongly inhibited ethylene production in the aged tissue. In the presence of ACC, however, ethylene production was not inhibited by AVG. These results suggest that ACC is an intermediate in the pathway of ethylene biosynthesis in the albedo tissue and that both steps of ACC formation and ACC conversion to ethylene are enhanced by wounding and aging. Inhibitors of protein synthesis, cycloheximide and 2-(4-methyl-2,6-dinitroanilino)-N-methyl propionamide, strongly inhibited ethylene production in the albedo tissue, implying that protein synthesis is required to maintain the continuous evolution of ethylene. The stimulation of ethylene production by ACC was reduced by the addition of l-methionine, whereas d-methionine had very little inhibitory effect. Ethylene production in the albedo tissue was also inhibited by the addition of n-propyl gallate and 3,5-dibromo-4-hydroxybenzoic acid.     

Salicylic acid inhibits the biosynthesis of ethylene in detached rice leaves

The effects of salicylic acid (SA) on ethylene biosynthesis in detached rice leaves were investigated. SA at pH 3.5 effectively inhibited ethylene production within 2 h of its application. It inhibited the conversion of ACC to ethylene, but did not affect the levels of ACC and conjugated ACC. Thus, the inhibitory effect of SA resulted from the inhibition of both synthesis of ACC and the conversion of ACC to ethylene.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene-forming enzyme - SA salicylic acid     

Rapidly induced ethylene formation after wounding is controlled by the regulation of 1-aminocyclopropane-1-carboxylic acid synthesis

Bean leaves from Phaseolus vulgaris L. var. Pinto 111 react to mechanical wounding with the formation of ethylene. The substrate for wound ethylene is 1-aminocyclopropane-1-carboxylic acid (ACC). It is not set free by decompartmentation but is newly synthesized. ACC synthesis starts 8 to 10 min after wounding at 28°C, and 15 to 20 min after wounding at 20°C. Aminoethoxyvinylglycine (AVG), a potent inhibitor of ethylene formation from methionine via ACC, inhibits wound ethylene synthesis by about 95% when applied directly after wounding (incubations at 20°C). AVG also inhibits the accumulation of ACC in wounded tissue. AVG does not inhibit conversion of ACC to ethylene. Wound ethylene production is also inhibited by cycloheximide, n-propyl gallate, and ethylenediaminetetraacetic acid.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG ammoethoxyvinylglycine - EDTA ethylenediaminetetraacetic acid     

Phytochrome-controlled ethylene biosynthesis of intact etiolated bean seedlings

Intact etiolated bean (Phaseolus vulgaris L. cv. Limburgse vroege) seedlings were illuminated with red light (10.5 W·m^-2) for 10 min. After different time intervals ethylene production, and contents of 1-aminocyclopropane-1-carboxylic acid (ACC) and 1-(malonylamino)cyclopropane-1-carboxylic acid were measured. The red-light-induced decrease of ethylene production in 8-d-old intact etiolated bean seedlings was fast, strong and long-lasting ad was mediated through the phytochrome system. This effect appeared to be strictly age-dependent, as it could not be detected in plants younger than 6 d or older than 11 d.The capacity for the conversion of ACC to ethylene was not affected by red light. The inhibitory effect of the light treatment on ethylene production could be related to a reduced free-ACC content. This reduction was a consequence of a temporary non-reversible increase of ACC malonylation and a long-lasting, for a certain time reversible, inhibition of ACC synthesis. The effect of a brief irradiation with red light on the decrease of ethylene production and free-ACC content was completed after about 2 h. Reversibility by far-red, however, persisted for at least 3 h, and was lost between 3 and 6 h.Abbrevation ACC 1-aminocyclopropane-1-carboxylic acid - M-ACC 1-(malonylamino)cyclopropane-1-carboxylic acid     

Effect of paraquat on ethylene biosynthesis by intact green Phaseolus vulgaris seedlings

Ethylene production by intact green bean ( Phaseolus vulgaris L. cv. Limburgse vroege) seedlings was investigated in white light and in darkness. In white light both endogenous and 1-aminocyclopropane-1-carboxylic acid (ACC)-induced ethylene production were stimulated. A decrease in the 1-(malonylamino)cyclopropane-1-carboxylic acid (M-ACC) level and a slight increase in the free ACC concentration could be observed in light. The total amount of endogenous ACC was not changed by light. We related the effect of light to the effect of paraquat on ethylene biosynthesis. Paraquat caused a strong increase of endogenous ethylene production in light. However, the conversion of exogenously applied ACC in light was not influenced by the paraquat treatment, although the presence of the herbicide in the chloroplasts was evident through the inhibition of net photosynthesis. In light, paraquat increased the total ACC content. This was due to an enlargement of the free ACC pool. The effects of white light and paraquat on ethylene biosynthesis can be differentiated from one another: white light exerts its influence on the conversion of ACC to ethylene; it also seems to inhibit the malonylation and may act on the formation of ACC itself. Paraquat influences only ACC synthesis.     

Rhythmicity in cotton seedlings

Ethylene production by detached cotyledons of cotton (Gossypium hirsutum L.) seedlings grown under cycles of 12 h darkness and 12 h light has been shown to be rhythmic, with a minimum and maximum 4 and 16 h, respectively after the start of the cycle (Rikin, Chalutz and Anderson, 1984, Plant Physiol. 75, 493–495). Treatment with silver ions stimulated the rhythmic ethylene production in both regular and inverted cycles (i.e. dark period changed to light period, and vice versa). The rate of the conversion of [3,4-¹⁴C]methionine into ethylene also followed the stimulation of rhythmic ethylene evolution by silver ions in both regular and inverted cycles, while treatment with aminoethoxyvinylglycine (AVG) decreased this stimulation. Conversion of exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) into ethylene was not affected by silver ions, but was dependent upon the immediate light conditions, regardless of the time in the light-dark cycle, light decreasing and darkness increasing this process. It is concluded that silver ions stimulate the normal rhythmic ethylene production, and this stimulation is regulated at a step prior to the conversion of ACC into ethylene. The rhythmicity in other processes (cotyledon movement, phenylalanine ammonia-lyase activity, resistance to the herbicide 3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide [bentazon]) was not affected by a decrease in the rhythmic changes in ethylene production by AVG or interference in ethylene action by silver ions. Thus, these rhythmic changes were not regulated by the rhythmic changes in ethylene production.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethyoxyvinylglycine - PAL phenylalanine ammonia-lyase     

Ethylene formation in Pisum sativum and Vicia faba protoplasts

Protoplasts isolated from leaves of peas (Pisum sativum L.) and of Vicia faba L. produced 1-aminocyclopropane-1-carboxylic acid (ACC) from endogenous substrate. Synthesis of ACC and conversion of ACC to ethylene was promoted by light and inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and carbonyl cyanide m-chlorophenylhydrazone. Aminoethoxyvinylglycine inhibited ethylene synthesis to a minor extent when given during incubation of the protoplasts but was very effective when added both to the medium in which the protoplasts were isolated and to the incubation medium as well. Radioactivity from [U-¹⁴C]methionine was incorporated into ACC and ethylene. However, the specific radioactivity of the C-2 and C-3 atoms of ACC, from which ethylene is formed, increased much faster than the specific radioactivity of ethylene. It appears that ACC and ethylene are synthesized in different compartments of the cell and that protoplasts constitute a suitable system to study this compartmentation.Abbreviations ACC 1-Aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - CCCP carbonyl cyanide m-chlorophenylhydrazone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Induction of ethylene synthesis and lipid peroxidation in damaged or TMV-infected tobacco leaf tissues by light

The effect of light on ethylene and ethane production in damaged leaf tissues was investigated. When whole leaves of tobacco cv. Samsun NN were damaged with liquid nitrogen, the ethylene formation was the highest, if 100?% of leaves were injured and were kept in the light, the lowest when leaves after 100?% injury were kept in darkness. Ethane production (lipid peroxidation) could be detected only in damaged, but not in control leaves, and was much higher in light than in darkness. In addition, there was a strong degradation of chlorophyll of damaged leaves kept in light. In light aminoethoxy-vinylglycine (AVG) inhibited ethylene formation in control, non-damaged whole leaves effectively, but in leaves with 100?% damage the inhibitory effect was much weaker and similar to the effect of propyl gallate (PG), a free radical scavenger. Both AVG and PG treatments decreased ethylene formation by control leaf discs and discs with 100?% damage. Ethane production was significantly inhibited by PG and slightly by AVG in the case of 100?% damage. Tiron, another free radical scavenger gave similar results on leaf discs as PG did. Paraquat (methylviologen, Pq), as a photosynthesis inhibiting and reactive oxygen species (ROS) producing herbicide produced a large amount of ethylene and ethane in light but very small amount in darkness. In accordance, tobacco mosaic virus (TMV) infection on the necrotic host resulted in significantly larger amount of ethylene and ethane formation in light than in darkness. We conclude that ethylene and ethane production of damaged plant tissues is strongly induced by light and ROS that are involved in this induction.     

A comparison of the conversion of 1-amino-2-ethylcyclopropane-1-carboxylic acid stereoisomers to 1-butene by pea epicotyls and by a cell-free system

The characteristics of the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene by pea (Pisum sativum L.) epicotyls and by pea epicotyl enzyme are compared. Of the four stereoisomers of 1-amino-2-ethylcyclopropane-1-carboxylic acid (AEC), only (1R,2S)-AEC is preferentially converted to 1-butene in pea epicotyls. This conversion is inhibited by ACC, indicating that butene production from (1R,2S)-AEC and ethylene production from ACC are catalyzed by the same enzyme. Furthermore, pea epicotyls efficiently convert ACC to ethylene with a low K _m (66 M) for ACC and do not convert 4-methylthio-2-oxo-butanoic acid (KMB) to ethylene, thus demonstrating high specificity for its substrate. In contrast, the reported pea epicotyl enzyme which catalyzes the conversion of ACC to ethylene had a high K _m (389 mM) for ACC and readily converted KMB to ethylene. We show, moreover, that the pea enzyme catalyzes the conversion of AEC isomers to butene without stereodiscrimination. Because of its lack of stereospecificity, its low affinity for ACC and its utilization of KMB as a substrate, we conclude that the reported pea enzyme system is not related to the in-vivo ethylene-forming enzyme.Abbreviations ACC 1-Amino cyclopropane-1-carboxylic acid - AEC 1-amino-2-ethylcyclopropane-1-carboxylic acid - EFE ethylene-forming enzyme - KMB 4-methylthio-2-oxobutanoic acid     

Ethylene biosynthesis in Regnellidium diphyllum and Marsilea quadrifolia

The pathway of ethylene biosynthesis was examined in two lower plants, the semi-aquatic ferns Regnellidium diphyllum Lindm. and Marsilea quadrifolia L. As a positive control for the ethylene-biosynthetic pathway of higher plants, leaves of Arabidopsis thaliana (L.) Heynh. were included in each experiment. Ethylene production by Regnellidium and Marsilea was not increased by treatment of leaflets with 1-aminocyclopropane-1-carboxylic acid (ACC), the precursor of ethylene in higher plants. Similarly, ethylene production was not inhibited by application of aminoethoxyvinylglycine and -aminoisobutyric acid, inhibitors of the ethylene biosynthetic enzymes ACC synthase and ACC oxidase, respectively. However, ACC was present in both ferns, as was ACC synthase. Compared to leaves of Arabidopsis, leaflets of Regnellidium and Marsilea incorporated little [¹⁴C]ACC and [¹⁴C]methionine into [¹⁴C]ethylene. From these data, it appears that the formation of ethylene in both ferns occurs mainly, if not only, via an ACC-independent route, even though the capacity to synthesize ACC is present in these lower plants.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AdoMet S-adenosyl-l-methionine - AIB -aminoisobutyric acid - AVG aminoethoxyvinylglycine This research was supported by the U.S. Department of Energy through grant No. DE-FG02-91ER20021 and, in part, by a fellowship of the National Engineering and Research Council of Canada to Jacqueline Chernys.     

Apical localization of 1-aminocyclopropane-1-carboxylic acid and its conversion to ethylene in etiolated pea seedlings

The biosynthetic basis for the high rates of ethylene production by the apical region of etiolated pea (Pisum sativum L.) seedlings was investigated. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) was quantified in extracts of various regions of seedlings by measuring isotopic dilution of a ²H-labelled internal standard using selected-ion-monitoring gas chromatography/mass spectrometry. The ACC levels in the apical hook and leaves were much higher than in the expanded internodes of the epicotyl. The capacity of excised tissue sections to convert exogenous ACC to ethylene was also much greater in the apical region, reflecting the distribution of soluble protein in the epicotyl.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - FW fresh weight - GC/MS coupled gas chromatography/mass spectrometry - HPLC high-performance liquid chromatography     

Circadian Ethylene Synthesis in <Emphasis Type="Italic">Sorghum bicolor</Emphasis>: Expression and Control of the System at the Whole Plant Level

Ethylene production by sorghum is rhythmic and the amplitude of the rhythm is increased both by dim, far-red enriched light and in mutant plants deficient in phytochrome B. The mechanisms involved in controlling ethylene production were examined in detail by measuring the rate of ethylene production among organs and tissues, examining the organ-specific levels of ACC (1-aminocyclopropane-1-carboxylic acid, the ethylene precursor) and investigating the contribution of the roots to shoot ethylene production. The results demonstrate that the expanding leaves were the major source of ethylene under dim, far-red enriched light and in the phytochrome B mutant. Enhanced ethylene production by the expanding leaf appeared to be the result of targeted delivery of ACC to this tissue. Root ACC levels were much higher than those in the shoot but roots converted much less of this endogenous ACC to ethylene. Applying ACC to the roots had only a marginal effect on their ethylene production, but greatly increased that of the shoots. Decapitated shoots continued to produce ethylene in a rhythmic pattern but the amplitude decreased with time compared to intact plants. The results collectively suggest that some, but not all, of the shoot ethylene rhythm depends on the transport of ACC from the roots to the shoots.     

Differential expression of antisense in regenerated tobacco plants transformed with an antisense version of a tomato ACC oxidase gene

Ethylene production was measured during vegetative and reproductive development in normal tobacco plants and in transgenic tobacco plants carrying antisense genes for tomato ACC oxidase driven by the 35S CaMV promoter (Hamilton et al., 1990). When expressed in three independently derived transgenic plants, the antisense ethylene gene failed to affect ethylene production in young/mature leaves or in stems but it did inhibit ethylene production in roots by 37–58%. Ethylene production in developing flowers (i.e. from small unopened flower buds up until open flowers at anthesis) was not affected in transgenic plants but ethylene production in fruits was inhibited by 35%. The most dramatic effect on ethylene production in transgenic plants was seen immediately after wounding leaf tissue, in which case the antisense gene inhibited wound ethylene production by 72%. Thus, the antisense gene composed of a 35S CaMV promoter driving a heterologous ACC oxidase sequence had differential effects on ethylene production in tobacco plants.     

The effect of light and dark periods on the production of ethylene from water-stressed wheat leaves

Light was found to inhibit substantially (i.e. up to 88%) the production of ethylene induced by water stress in excised wheat leaves and from the shoots of intact plants. The relatively small amounts of ethylene emanating fron non-stressed leaves were also inhibited by light but to a smaller degree (i.e. up to 61%). In water-stressed leaves the degree of light inhibition of ethylene production was shown to be related to the age of the leaves; the amounts of ethylene diffusing from young leaves (i.e. 6-days old) was inhibited 52% by light whereas in older leaves (i.e. 9-days old) it was inhibited by 85%. Previous studies [Wright (1979) Planta 144, 179–188 and (1980) Planta 148, 381–388] had shown that application of 6-benzyladenine (BA) to leaves a day before wilting, greatly increases the amount of ethylene diffusing from the leaves following wilting (e.g. 8-fold), and to smaller degrees do applications of indole-3-acetic acid (IAA) and gibberellic acid (GA₃). On the other hand abscisic acid (ABA) treatment reduces the amount of ethylene produced. In these earlier experiments the ethylene was collected from leaves held under dark or near-dark conditions, so in the present study the activities of these growth regulators (10^-4 mol l^-1 solutions) under dark and light conditions were compared. It was found that they maintained the same relative activities on ethylene emanation (i.e. BA>IAA>GA₃>water controls>ABA) under both light and dark conditions. However, because of the inhibitory effect of light, the absolute amounts of ethylene produced from all treatments were always much higher in the dark than in the light (usually about a 6-fold difference). An interesting effect of light treatment on ethylene biosynthesis was found when water-stressed leaves were kept in dark chambers for 41/2 h and then transferred to light. Quite unexpectedly, instead of the rate of ethylene production falling immediately, it continued to be produced at the dark rate (i.e. no light inhibition!) for over 2 h before the rate began to decline, and for a much longer period (i.e. in excess of 41/2 h) if the leaves had previously been sprayed with BA. Predictably, leaves placed in the light (i.e. in leaf chambers) and then transferred to darkness, immediately or very soon produced ethylene at the dark rate. One explanation of these results, which is discussed, would be that the biosynthesis of an ethylene precursor requires an obligatory dark stage. The possible implications of these studies to a survival role of ethylene in plants during periods of water stress is discussed.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - BA 6-benzyladenine - GA₃ gibberellic acid - GLC gas-liquid chromatography - IAA indole-3-acetic acid - TLC thin-layer chromatography - _leaf leaf water potential     

The isolation and physiological analysis of mutants of the moss,Physcomitrella patens,which over-produce gametophores

We have compared the effects of cycloheximide (CHI) and two other rapid and effective inhibitors of protein synthesis, pactamycin and 2-(4-methyl-2,6-dinitroanilino)-N-methyl proprionamide (MDMP), on protein synthesis, respiration, auxin-induced growth and H⁺-excreation of Avena sativa L. coleoptiles. All three compounds inhibit protein synthesis without affecting respiration. The effectiveness of the inhibitors against H⁺-excretion and growth correlates with their ability to inhibit protein synthesis. Both CHI and MDMP inhibit auxin-induced H⁺-excretion after a latent period of 5–8 min, and inhibit growth after a 8–10-min lag. These results support the idea that continued protein synthesis is required in the initial stages of the growth-promoting action of auxin.Abbreviations CHI cycloheximide - DMSO dimethyl sulfoxide - FC fusicoccin - IAA indole-3-acetic acid - MDMP 2-(4-methyl-2,6-dinitroanilino)-N-methyl proprionamide