Metabolism of 1-Aminocyclopropane-l-Carboxylic Acid during Apple Fruit Development

The metabolism of [U^–14C] 1-aminocyclopropane-1-carboxylicacid (ACC) supplied to whole fruits of apple (Malus domesticaBorkh., cv. Cox's Orange Pippin) was investigated. Radioactiveethylene was recovered in mercuric acetate traps and an acidicmetabolite was formed in proportions which varied little withthe absolute amount of substrate supplied. The amount of ACCusually supplied did not cause immediate, rapid ethylene productionby mature, pre-climacteric fruit but the onset of productionwas earlier than in untreated fruit. The radioactive acidic metabolite was purified by four chromatographicprocedures and activity was coincident with authentic 1-malonylamino)cyclopropane-1-carboxylic acid (MACC). The presence of thiscompound was confirmed by gas chromatography linked to massspectrometry. MACC was a major metabolite of [¹⁴C] ACC supplied to applesthroughout fruit development. The proportion converted to ethylenewas low but increased with endogenous ethylene production inthe final samples. MACC was shown to be a natural constituent of apple fruits andto accumulate to the amol kg^–1 level. Key words: 1-Aminocyclopropane-l-carboxylic acid, Ethylene, 1 (Malonylamino) cyclopropane-1-carboxylic acid, Malus domestica     

The Effects of Oxygen, Carbon Dioxide and Ethylene on Ethylene Biosynthesis in Relation to Shoot Extension in Seedlings of Rice (Oryza sativa) and Barnyard Grass (Echinochloa oryzoides)

Exposing dark-grown seedlings for 3 d to oxygen deficiency (0or 5 kPa) or to additions of carbon dioxide (10 kPa) or ethylene(0·1 Pa) slowed shoot extension in Echinochloa oryzoides,while in rice it was promoted by these treatments, except that5 kPa oxygen was without effect. In E. oryzoides this was dueto reduced growth of the mesocotyl, and in rice to enhancedgrowth of the coleoptile. These responses to carbon dioxideand oxygen deficiency were not consequences of increased ethyleneproduction, since this remained unchanged by carbon dioxideand depressed by oxygen shortage in both species. Furthermore,exogenous ethylene and the ethylene action inhibitor 2,5-norbornadieneeach failed to influence extension in anoxic seedlings, indicatingno regulatory role for ethylene in the absence of oxygen. However,concentrations of the ethylene precursor 1 -aminocyclopropane-1-carboxylic acid (ACC) were increased by carbon dioxide and0 kPa or 5 kPa oxygen, although after 72 h without oxygen totalACC production (i.e. changes in ethylene + ACC + MACC) was suppressedin both species. There was little effect on bound ACC [putativemalonyl-ACC (MACC)] formation. Transferring anaerobic (0 kPa)seedlings to oxygenated conditions (21 kPa) resulted in abnormallyfast rates of ethylene formation, possibly due to the accumulationof ACC under anoxia. This post-anoxic ethylene may have contributedto the faster extension by rice coleoptiles and slower extensionby mesocotyls of E. oryzoides compared with those of seedlingsmaintained continuously in air. Echinochloa oryzoides [Ard.] Fritsch, barnyard grass, Oryza sativa L, rice, oxygen shortage, carbon dioxide, ethylene biosynthesis, shoot extension, 1-aminocyclopropane-1-carboxylic acid (ACC), malonyl-ACC, GC-MS     

Changes in Ethylene Production and in 1-Aminocyclopropane-1-carboxylic Acid (ACC) and Malonyl-ACC Contents of Cocklebur Seeds during Their Development

Ethylene production in developing cocklebur (Xanthium pennsyluanicumWallr.) seeds peaked when the dry weight of the seeds beganto increase in the early period of development. The productionthen began to decrease and stopped when the dry weight increasewas completed. The upsurge of ethylene production in the earlydevelopmental period paralleled increases in ACC synthase activityand the 1-aminocyclopropane-1-carboxylic acid (ACC) contentof the seeds, both of which rapidly decreased later. Malonyl-ACC (MACC) accumulated in developing cocklebur seedsduring the early period of development, before the ACC contentand ethylene production increased. Although the ACC synthaseactivity, ACC content and ethylene production showed markeddecreases, the MACC content remained almost unchanged duringthe middle period of seed development, with a pronounced decreaseoccurring in the late period. Exogenous application of MACCdid not promote ethylene production of seeds collected at thelate developmental stage. Aminoethoxyvinylglycine, an inhibitorof ACC synthase, strongly inhibited the ethylene productionof the same lot of seeds. Therefore, the decrease in the MACCcontent in developing cocklebur seeds was not due to reuse ofMACC for ethylene production. (Received May 24, 1984; Accepted August 15, 1984)     

The Conversion of 1-(Malonylamino)cyclopropane-1-Carboxylic Acid to 1-Aminocyclopropane-1-Carboxylic Acid in Plant Tissues

Since 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), the major conjugate of 1-aminocyclopropane-1-carboxylic acid (ACC) in plant tissues, is a poor ethylene producer, it is generally thought that MACC is a biologically inactive end product of ACC. In the present study we have shown that the capability of watercress (Nasturtium officinale R. Br) stem sections and tobacco (Nicotiana tabacum L.) leaf discs to convert exogenously applied MACC to ACC increased with increasing MACC concentrations (0.2-5 millimolar) and duration (4-48 hours) of the treatment. The MACC-induced ethylene production was inhibited by CoCl₂ but not by aminoethoxyvinylglycin, suggesting that the ACC formed is derived from the MACC applied, and not from the methionine pathway. This was further confirmed by the observation that radioactive MACC released radioactive ACC and ethylene. A cell-free extract, which catalyzes the conversion of MACC to ACC, was prepared from watercress stems which were preincubated with 1 millimolar MACC for 24 hours. Neither fresh tissues nor aged tissues incubated without external MACC exhibited enzymic activity, confirming the view that the enzyme is induced by MACC. The enzyme had a K_m of 0.45 millimolar for MACC and showed maximal activity at pH 8.0 in the presence of 1 millimolar MnSO₄. The present study indicates that high MACC levels in the plant tissue can induce to some extent the capability to convert MACC to ACC.     

Intracellular Sites of Synthesis and Storage of 1-(Malonylamino)cyclopropane-1-Carboxylic Acid in Acer pseudoplatanus Cells

Vacuoles were isolated from Acer pseudoplatanus cells that were incubated with [¹⁴C]1-aminocyclopropane-1-carboxylic acid (ACC). The kinetics of [¹⁴C]1-(malonylamino)cyclopropane-1-carboxylic acid (MACC) formation are consistent with the interpretation that MACC is synthesized in the cytosol, transported through the tonoplast, and accumulated in the vacuole. Twenty hours after chasing the labeled ACC with unlabeled ACC and adding 1 millimolar unlabeled MACC, all the [¹⁴C]MACC synthesized is located in the vacuole. Whole cells preloaded with [¹⁴C]MACC and then submitted to a continuous washing out, readily release their cytosolic MACC until complete exhaustion. The half-time of MACC efflux from the cytosol, calculated by the technique of compartmental analysis, is about 22 minutes. In contrast, vacuolar MACC remains sequestered within the vacuole. The transport of labeled MACC into the vacuole is stimulated by the presence of unlabeled MACC in the suspension medium, probably as a result of a reduced efflux of the labeled MACC from the cytosol into the suspending medium.     

The quantification of 1-(malonylamino)cyclopropane-1-carboxylic acid in plant tissues by quantitative mass spectrometry

A method for the quantitation of 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), a conjugated form of 1-aminocyclopropane-1-carboxylic acid (ACC), in plants is described. [2,2,3,3-²H₄]MACC has been used as an internal standard for selected ion monitoring/isotope dilution quantitation of MACC in wheat seedlings and in tomato leaves. This method is compared with a widely-used two step indirect assay for MACC, which is based upon hydrolysis of MACC to ACC and conversion of ACC by hypochlorite reagent to ethylene which is subsequently quantified by gas chromatography.     

Interrelationship between the Different Flower Parts during Emasculation-Induced Senescence in Cymbidium Flowers

In Cymbidium flowers emasculation by removal of the anther capand the pollinia, led to rapid colouration of the lip and advancedwilting of the petals and sepals. The ethylene production ofwhole flowers showed an emasculation-induced early peak in ethyleneevolution followed some days later by a second increase concomitantwith the wilting of the flower. In non-emasculated flowers theethylene production increased later and simultaneously withcolouration of the lip and wilting of the petals and sepals.At all stages of senescence, the contribution of the lip, petals,and sepals to the total amount of ethylene produced was negligible. Parallel to the increase in ethylene production of whole flowers,an increase in 1-aminocyclopropane-l-carboxylic acid (ACC) andmalonyl-ACC (MACC) in the central column and, to a lesser extent,in the ovary was observed. Also an increase in internal ethyleneconcentration was demonstrated and this, in contrast, was apparentin all the different flower parts. The activity of the ethylene-formingenzyme in lips, petals, and sepals showed an increase afteremasculation and such an effect could also be induced by treatmentof isolated lips with low concentrations of ethylene. The data indicate that senescence in Cymbidium flowers is regulatedby the central column and perhaps the ovary and that both ACCand ethylene may play a signalling role in inter-organ communication. Key words: 1-aminocyclopropane-l-carboxylic acid, ethylene, Cymbidium, senescence     

The effect of water stress on 1-(malonylamino)cyclopropane-1-carboxylic acid concentration in plant tissues

Since the discovery of1-(malonylamino)cyclopropane-1-carboxylic acid (MACC)as a major metabolite of both endogenous andexogenously applied 1-aminocyclopropane-1-carboxylicacid (ACC), it has become evident that the formationof MACC from ACC can act to regulate ethyleneproduction in certain tissues. Hence it was suggestedthat MACC could serve as an indicator of water-stresshistory in plant tissues. The accurate quantificationof MACC in plant tissues is essential forunderstanding the role of MACC in the regulation ofethylene biosynthesis.Hoffman et al. [15] described a method for themeasurement of MACC in which MACC was hydrolysed byHCl to ACC, which was then assayed by chemicaloxidation to form ethylene. Attempts have been made byothers to raise monoclonal antibodies to MACC so thatan immunoassay could be developed in order to gain adeeper understanding of stress-induced ethyleneproduction but no further publications have beenforthcoming.Here a method employing GC-MS is compared with theindirect assay for MACC, which is based uponhydrolysis of MACC to ACC and conversion of ACC byhypochlorite reagent to ethylene which is subsequentlyquantified by GC.     

Knockdown of MACC1 expression suppressed hepatocellular carcinoma cell migration and invasion and inhibited expression of MMP2 and MMP9

Expression of MACC1 (metastasis-associated in colon cancer-1) protein is associated with metastasis of various human cancers. This study analyzed MACC1 protein expression in hepatocellular carcinoma (HCC) tissue specimens and then investigated the effects of MACC1 knockdown on HCC cell migration and invasion, and gene expression levels. Sixty pairs of HCC and adjacent normal liver tissues from HCC patients were analyzed for MACC1 expression immunohistochemically. The HCC cell lines Hep3B, Huh7, MHCC97H, SMMC-7721, Bel-7402, and HepG2 and the normal liver cell line LO2 were used to assess expressions of MACC1 mRNA and MACC1 protein using qRT-PCR and western blot, respectively. MACC1 short hairpin RNA (shRNA) was used to knockdown MACC1 protein expression in Huh7 cells. Changes in the tumor phenotype of these cells were analyzed with wound healing assay and invasion assays, and differences in gene expression were evaluated via western blot. Immunofluorescence was used to locate MACC1 protein in the above cell lines. MACC1 was highly expressed in HCC tissues and the nuclear expression of MACC1 protein was associated with poor tumor differentiation and intrahepatic metastasis or portal invasion. Moreover, MACC1 mRNA and MACC1 protein was also expressed in HCC cell lines. Immunostaining showed that MACC1 protein was localized in both nuclei and cytoplasm of HCC cell lines and the nuclear localization of MACC1 protein was associated with increased aggressiveness of HCC in cell lines. Knockdown of MACC1 expression using MACC1-shRNA reduced Huh7 cell migration and invasion abilities, which was associated with downregulation of MMP2, MMP9, and c-Met proteins in Huh7 cells. Localization of MACC1 protein to the nucleus may predict HCC progression. Knockdown of MACC1 expression using MACC1 shRNA warrants further evaluation as a novel therapeutic strategy for control of HCC.     

Changes in 1-(malonylamino)cyclopropane-1-carboxylic acid content in wilted wheat leaves in relation to their ethylene production rates and 1-aminocyclopropane-1-carboxylic acid content

In excised wheat (Triticum aestivum L.) leaves, water-deficit stress resulted in a rapid increase, followed by a decrease, in ethylene production rates and in the levels of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene. However, the level of N-malonyl-ACC (MACC), the major metabolite of ACC, increased gradually, then leveled off. This increase in MACC was much greater than the decrease in ACC level. The MACC levels were positively correlated with severity of water stress. Once established, the MACC levels did not decrease even after the stressed tissues were rehydrated. Administration of labeled ACC and MACC showed that the conjugation of ACC to MACC was essentially irreversible. Repeated wilting treatments following the first wilting and rehydration cycle resulted in no further increase in ethylene production and in the levels of ACC and MACC. However, when benzyladenine was supplied during the preceding rehydration process, subsequent wilting treatment resulted in a rise in MACC level and a rapid rise followed by a decline in ethylene production rates and in the level of ACC. The magnitude of these increases was, however, smaller in these rewilted tissues than that observed in the first wilting treatment. Since MACC accumulates with water stress and is not appreciably metabolized, the MACC level is a good indicator of the stress history in the detached leaves used.     

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.     

Changes in the level of MACC during cold hardening and dehardening in winter wheat

Changes in the level of 1-(malonylamino)-cyclopropane-1-carboxylic acid (MACC) were determined in 6 winter wheat cultivars during cold hardening at 4°C. The cultivars differed by one degree of frost resistance within the range of degree II to VII of the COMECON scale. The time-course of changes in MACC level showed a similar pattern in all 6 cultivars; i.e. increase till day 6, no changes for the next 10 days, and then a steady decrease till the end of the hardening period. There was little difference between the final and the initial levels. The increase of MACC level, expressed as per cent of the original level, was not directly correlated with either the degree of frost resistance of the actual percentage of survival. In some cultivars. mean errors exceeded the difference in MACC accumulation between cultivars closest on the resistance scale.
The fate of MACC during the second half of hardening and after transfer of plants to 25°C was studied in cultivars Bezostaya and San Pastore. During the second half of the hardening period the level of MACC decreased in the leaves of both cultivars, but increased significantly in the roots. Within two days of transfer of the hardened plants to 25°C, the MACC level in leaves increased again, while that in the roots decreased. This finding, together with the preliminary evidence of very low MACC metabolism, strongly suggest that MACC accumulates in roots during the hardening period and when transferred to 25°C, it moves from roots to leaves.     

Effects of Cold Acclimation and Salicylic Acid on Changes in ACC and MACC Contents in Maize during Chilling

The effect of 0.5 mM salicylic acid (SA) pretreatment and of growing at hardening temperatures on chilling-induced changes in 1-aminocyclopropane-1-carboxylic acid (ACC) and malonyl 1-aminocyclopropane-1-carboxylic acid (MACC) was investigated in young maize (Zea mays L.) plants grown in hydroponic solution at 22/20 °C. Chilling at 5 °C caused an increase in ACC content;however, this increase was less pronounced in plants cold acclimated at 13/11 °C 4 d before the chilling treatment, and in those which were pretreated with SA for 1 d before the cold stress. Changes in MACC at low temperature showed no correlation with chilling tolerance in maize.     

Levels of ethylene, ACC, MACC, ABA and proline as indicators of cold hardening and frost resistance in winter wheat

Changes in ethylene production and in the contents of 1-aminocydopropane-1-carboxylic acid (ACC), 1-(malonylamin6)-cyclopropane-1-carboxylic acid (MACC), abscisic acid (ABA) and L-proline were determined after 40 days of cold hardening at 4°C in three wheat cultivars differing in frost resistance. Proline and especially ABA accumulated with hardening in all varieties in parallel with the degree of frost resistance, e.g. proline and ABA increases in the non-resistant cv. Slávia were 2x and 5x, whilst in the resistant cv. Mironovská 808 increases were 4X and 20X. Ethylene production and MACC level showed no significant changes with hardening in any of the cultivars after 40 d, but ACC levels did increase with hardening. The production of ethylene, ACC and MACC was studied during hardening. Ethylene production decreased sharply at low temperature and rose rapidly (within 1 day) on return to normal temperature, while ACC production reacted in the opposite direction. MACC levels rose rapidly during the first 4 days of cold, then more slowly for about 2 weeks, thereafter decreasing again steadily. The only varietal differences occurring at maximum levels were correlated with the degree of frost resistance.     

Significance of plasma MACC1 levels on the prognostic stratification in patients with colorectal cancer

The clinical significance of metastasis‐associated in colon cancer‐1 (MACC1) has been investigated but the relevance of peripheral MACC1 levels was rather limited. Herein, our data revealed that plasma MACC1 levels in 117 colorectal cancer patients (CRC) were dramatically higher than that in normal controls (P < 0.001), and with a strong discrimination power between the two groups (AUC = 0.960, P < 0.001). Moreover, MACC1 is an independent prognostic factor for CRC patients. When clinical parameters stratified by MACC1_low and MACC1_high, MACC1 levels exhibited further significant predictive value. Summary, plasma MACC1 levels could be a useful prognostic and diagnostic biomarker, and could improve the prognostic value of traditional prognosticators for colorectal cancer patients.     

Activity of Ageing Carnation Flower Parts and the Effects of 1-(Malonylamino)cyclopropane-1-Carboxylic Acid-Induced Ethylene

Peak levels of 1-aminocyclopropane-l-carboxylic acid (ACC) in flower parts of ageing carnations (Dianthus caryophyllus L. cv Scanea 3C) were detected 6 to 9 days after flower opening. The ethylene climacteric and the first visible sign of wilting was observed 7 days after opening. The concentration of conjugated ACC in these same tissues peaked at day three with reduction of 70% by day 4. From day 5 to day 9 all parts followed a diurnal pattern of increasing in conjugate levels 1 day and decreasing the next. Concentrations of conjugated ACC were significantly higher than those of ACC in all ageing parts. Preclimacteric petals treated with ACC or 1-(malonylamino)-cycloprane-1-carboxylic acid (MACC), started to senesce 30 to 36 hours after treatment. When petals were treated with MACC plus by 0.1 millimolar aminoethyoxyvinylglycine, premature senescence was induced, while ethylene production was suppressed relative to MACC-treated petals. Petals treated with MACC and silver complex produced ethylene, but did not senesce. The MACC-induced ethylene was inhibited by the addition of 1.0 millimolar CoC1₂. These results demonstrate MACC-induced senescence in preclimacteric petals. The patterns of ACC and MACC detected in the flower parts support the view that an individual part probably does not export an ethylene precursor to the remainder of the flower inducing senescence.     

Porphyrinogenesis in maize as affected by bidentate chelators of iron

Intracellular compartmentation of 1-aminocyclopropane-1-carboxylic acid (ACC) and N-malonyl-1-aminocyclopropane-1-carboxylic acid (MACC) in wheat ( Triticum aestivum L. cv. Kanzler) and barley ( Hordeum vulgare L. cv. Gerbel) leaves was studied using different methods: first, the isolation of intact vacuoles from protoplasts and, second, a non-aqueous fractionation procedure. The two methods gave similar results. ACC concentrations were similar in the extravacuolar space and in the vacuole, whereas MACC was accumulated in the vacuolar space. Transport studies revealed that no specific carrier for ACC exists at the tonoplast. MACC transfer across the tonoplast was enhanced by 120% in the presence of ATP. MACC competitively inhibited malate transport into the vacuole indicating that the same transfer system catalyzes the transfer of the two dicarboxylates.
It is concluded that malonylation of ACC is not a prerequisite for the transport of ACC through the tonoplast.     

MACC1 Down-Regulation Inhibits Proliferation and Tumourigenicity of Nasopharyngeal Carcinoma Cells through Akt/β-Catenin Signaling Pathway

The present study was aimed at investigating the expression of metastasis-associated in colon cancer 1 (MACC1) in nasopharyngeal carcinoma (NPC), its relationship with β-catenin, Met expression and the clinicopathological features of NPC, and its roles in carcinogenesis of NPC. Our results showed that MACC1 expression was higher in NPC cells and tissues than that in normal nasopharyngeal cells and chronic inflammation of the nasopharynx tissues, respectively. MACC1 expression was closely related to the clinical stage (p = 0.005) and the N classification (p<0.05) of NPC. Significant correlations between MACC1 expression and Met expression (p = 0.003), MACC1 expression and β-catenin abnormal expression (p = 0.033) were found in NPC tissues. MACC1 knockdown dramatically inhibited cellular proliferation, migration, invasion, and colony formation, but induced apoptosis in NPC cells compared with the control group. Furthermore, MACC1 down-regulation inhibited phosphorylated-Akt (Ser473) and β-catenin expression in NPC cells, but phosphorylated-Erk1/2 expression was not altered. Further study showed that phosphotidylinsitol-3-kinase inhibitor downregulated β-catenin and Met expression in NPC cells. There was a significant relationship between MACC1 expression and phosphorylated-Akt expression (p = 0.03), β-catenin abnormal expression and phosphorylated-Akt expression (p = 0.012) in NPC tissue, respectively. In addition, Epstein Barr virus-encoded oncogene latent membrane protein 1 upregulated MACC1 expression in NPC cells. Our results firstly suggest that MACC1 plays an important role in carcinogenesis of NPC through Akt/β-catenin signaling pathway. Targeting MACC1 may be a novel therapeutic strategy for NPC.     

Carrier-Mediated Uptake of 1-(Malonylamino)cyclopropane-1-Carboxylic Acid in Vacuoles Isolated from Catharanthus roseus Cells

The uptake of 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), the conjugated form of the ethylene precursor, into vacuoles isolated from Catharanthus roseus cells has been studied by silicone layer floatation filtering. The transport across the tonoplast of MACC is stimulated fourfold by 5 millimolar MgATP, has a K_m of about 2 millimolar, an optimum pH around 7, and an optimum temperature at 30°C. Several effectors known to inhibit ATPase (N,N′-dicyclohexylcarbodiimide) and to collapse the transtonoplastic H⁺ electrochemical gradient (carbonylcyanide m-chlorophenylhydrazone, gramicidin, and benzylamine) all reduced MACC uptake. Abolishing the membrane potential with SCN⁻ and valinomycin also greatly inhibited MACC transport. Our data demonstrate that MACC accumulates in the vacuole against a concentration gradient by means of a proton motive force generated by a tonoplastic ATPase. The involvement of a protein carrier is suggested by the strong inhibition of uptake by compounds known to block SH—, OH—, and NH₂— groups. MACC uptake is antagonized competitively by malonyl-d-tryptophan, indicating that the carrier also accepts malonyl-d-amino acids. Neither the moities of these compounds taken separately [1-aminocyclopropane-1-carboxylic acid, malonate, d-tryptophan or d-phenylalanine] nor malate act as inhibitors of MACC transport. The absence of inhibition of malate uptake by MACC suggests that MACC and malate are taken up by two different carriers. We propose that the carrier identified here plays an important physiological role in withdrawing from the cytosol MACC and malonyl-d-amino acids generated under stress conditions.     

Changes m Ethylene Production in Relation to l-Aminocyclopropane-l-Carboxylic Acid and Its Malonyl Conjugate in Waterlogged Wheat Plants

When wheat seedlings were subjected to waterlogging, 1-aminocyelopropane-l-carboxylic acid (ACC), an ethylene precursor, accumulated in large quantity in roots. In shoots, ACC and ethylene production also increased, but declined with the prolonged periods of waterlogging. However, ACC content in roots maintained in high level during the whole period of waterlogging. Drainage caused a drastic drop in both ACC content and ethylene production in waterlogged plants to control level. 1-(malonylamino) cyclopropane-l-carboxylic acid (MACC) level in roots subjected to waterlogging showed little changes. However, MACC content in shoots kept increasing during the 9-days period of waterlogging. At later period of waterlogging (longer than 5 days) when ACC and ethylene production bad dropped, the. level of MACC continued to increase. Draining stopped this increasing, but did not reduced its level. When exogenous ACC was introduced into the leaves via transpiration stream, the ability of leaves of waterlogged plant to convert ACC to MACC was much higher than control. The data presented showed that at the later stage of waterlogging, the conversien of a great quantity of ACC to MACC in waterlogged wheat plants is the cause of the reduction of ethylene production and ACC content. It was suggested that the formation of MACC is another way of regulation in ethylene biosynthesis. Among leaves of different ages, the enhancement of ethylene, ACC and MACC content was more pronounced in older leaves than in younger laves during the waterlogging period. The physiological significance of adaptation to waterlogging stress was discussed.