Activities Of 1-aminocyclopropane-1-carboxylic Acid Research Articles

1-methylcyclopropene combined with ethylene absorbent delays the ripening of ‘Fenjiao’ banana (Musa ABB Pisang Awak)

The 'Fenjiao' banana (Musa ABB Pisang Awak) has a high commercial and nutritional value and is harvested when it is highly plump at between 85 and 90 % commercial maturity. The fruit are less angular at this stage. However, these fruit soften rapidly after harvest. 1-Methylcyclopropene (1-MCP) significantly delays ripening, but it can cause ripening disorders when used improperly. Ethylene absorbent (EA) is also widely used to increase the postharvest life of fruit, but it has less of an effect on 'Fenjiao' banana. This study was conducted to optimize the concentrations of 1-MCP combined with EA to increase the shelf life of these bananas. The results showed that a low concentration of 1-MCP (7 g L−1) combined with EA (2 g kg−1) significantly prolonged the shelf life of the 'Fenjiao' banana and maintained its high quality. The combination of 1-MCP and EA repressed the activities of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase, ACC synthase, pectin methylesterase, polygalacturonase and pectate lyase in the peel and pulp of 'Fenjiao' banana, as well as the corresponding levels of expression of MbACS1, MbACO1, MbPG1, MbPL1, except for MbPME1, which are induced by 1-MCP. This study provides a useful technique for preserving 'Fenjiao' fruit with a study on its possible physiological mechanism, which could be applied in the postharvest production of 'Fenjiao' banana.

Endophytic bacteria enhance the growth and salt tolerance of rice under saline conditions

Developing biostimulants from salt-tolerant plant growth-promoting (PGP) bacteria is an emerging strategy for sustainable agriculture in the context of increasing soil salinization. This study aimed to isolate endophytic bacteria (EB) capable of promoting rice seed germination and seedling growth at different NaCl concentrations. Nine salt-tolerant EB strains were isolated and two, ST.6 and ST.8, with the rice seed promoting effect 99.3 and 99.7 %, respectively, were selected and identified as Pantoea dispersa and Burkholderia cenocepacia, respectively. ST.6 showed a higher value of the activity of phosphatase (617 mg P ml-1), production of indole-3-acetic acid (19.7 µg IAA ml-1), the activity of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (13.5 µmol mg−1 protein h−1), and production of siderophore (76.3 %). Especially, rice seedlings inoculated with strain ST.6 showed a significant improvement in root length (58.95 %), shoot length (16.6 %), dry biomass (7.0 %), the content of chlorophyll (46.2 and 57.1 % for chlorophyll a and b, respectively), carotenoids (22.2%), and proline (19.0 %). A decrease in antioxidant enzyme activities was also observed in the rice seedlings inoculated with either ST.6 or ST.8 strain under salt stress. Furthermore, the salt stress condition enhanced the colonization of roots by both studied endophytic bacteria. More experiments should be done to develop endophytic bacteria ST.6 and ST.8 as efficient bio-inoculants.

Acetylsalicylic acid and salicylic acid alleviate postharvest leaf senescence in Chinese flowering cabbage (Brassica rapa var. parachinensis)

The leaves of ‘Ningxia Chinese flowering cabbage’ readily become yellow and senesce after harvest. To test the effects of acetylsalicylic acid (ASA) and salicylic acid (SA) on postharvest leafy vegetables, Chinese flowering cabbages were sprayed with 2 mmol L−1 ASA and 1.5 mmol L−1 SA, and stored at 15 °C. Compared with the controls, during storage, ASA- and SA-treated cabbages retained higher levels of total chlorophyll (Chl), Chl a, and Chl b, and lower activities of chlorophyllase, Mg dechelatase, pheophytinase, and Chl-degrading peroxidase, and had more intact chloroplasts. Furthermore, ASA and SA repressed respiration intensity, ethylene rate, the activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase, and ACC content, decreased reactive oxygen species (ROS) levels, and increased the activities of superoxide dismutase, catalase, ascorbate peroxidase, peroxidase, phenylalanine ammonia lyase, cinnamate 4-hydroxylase, 4-coumarate-CoA ligase, chalcone synthase, chalcone isomerase, and cinnamyl alcohol dehydrogenase, promoting the accumulation of phenolics and flavonoids. Using principal component and hierarchical clustering analyses, leaf senescence was attributed to higher respiration, ethylene synthesis, and ROS levels, while the delay of senescence in treated cabbages resulted from the cooperation of ROS metabolism and the phenylpropanoid pathway. ASA and SA slowed leaf degreening and senescence. Between the two treatments, 2 mmol L−1 ASA was the most effective.

Reducing plant-derived ethylene concentrations increases the resistance of temperate grassland to drought

Model predictions indicate that extreme drought events will occur more frequently by the end of this century, with major implications for terrestrial ecosystem functions such as plant productivity and soil respiration. Previous studies have shown that drought-induced ethylene produced by plants is a key factor affecting plant growth and development, but the impact of drought-induced ethylene on ecosystem functions in natural settings has not yet been tested. Here, we reduced the amount of plant-derived ethylene concentrations by adding the ethylene inhibitor aminoethoxyvinylglycine (AVG), and investigated in situ plant productivity, soil respiration and ethylene concentrations for two years in a semi-arid temperate grassland in Inner Mongolia, China. Drought significantly reduced plant productivity and soil respiration, but the application of AVG reduced ethylene concentrations and significantly increased aboveground plant productivity and soil respiration, effectively enhancing resistance to drought. The reason for this could be that AVG application increased the activity of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and abundance of the acdS gene (the key gene for ACC deaminase), facilitating reduced ACC concentrations in the plant tissue and reduced in planta ethylene synthesis. In addition, there was a significant correlation between soil ACC deaminase activity and plant productivity. Given the global distribution of arid and semi-arid areas, and the expected increases in the frequency and intensity of drought stress, this is a significant concern. These results provide novel evidence of the impact of drought-induced plant ethylene production on ecosystem functions in semi-arid temperate grassland ecosystems.

Delay of ripening and senescence in mango fruit by 6-benzylaminopurine is associated with inhibition of ethylene biosynthesis and membrane lipid catabolism

6-Benzylaminopurine (6-BA), a synthetic cytokinin compound, plays a vital role in modulating diverse physiological processes in plants and is widely applied in agriculture. This study aims to investigate the effects of 6-BA on ripening and senescence and its possible mechanisms in harvested ‘Guifei’ mango fruit. The results exhibited that the application of 0.2 g L−1 6-BA to mango fruit inhibited the changes in firmness, flesh color, soluble solids content (SSC), titratable acidity (TA) and contents of carotenoid and chlorophyll, while retarded the climacteric process of respiration and ethylene. The delay of ethylene production due to 6-BA application was correlated with suppressed activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) and ACC oxidase (ACO) in mango fruit. 6-BA treatment also reduced the accumulation of reactive oxygen species (ROS) (·O2- and H2O2) and malonaldehyde (MDA) and maintained a lower membrane permeability. Moreover, 6-BA treatment inhibited the activities of phospholipase D (PLD) and lipoxygenase (LOX) and downregulated the relative expression of MiPLD and MiLOX, which resulted in reduced degradation of phosphatidylcholine (PC) to phosphatidic acid (PA) and limited lipid peroxidation. The results suggest that 6-BA could delay ripening and senescence in mango fruit through regulating ethylene biosynthesis, ROS production and membrane lipid metabolism.

Methyl jasmonate alleviates the reduced release of aroma‐related esters in ‘Nanguo’ pears by regulating ethylene biosynthesis and signal transduction

SummaryCryopreserved fruits usually develop symptoms, which affects the release of aroma. Our study investigated the impact of exogenous methyl jasmonate (MeJA) upon the synthesis of aromatic esters in ‘Nanguo’ pears after cold storage. It found that exogenous MeJA enhanced ethylene accumulation via improving the activity of 1‐aminocyclopropane‐1‐carboxylic‐acid (ACC) synthase (ACS) and ACC oxidase (ACO) and the expression levels of PuACS1 and PuACO1. After cryopreservation for 90 days, the ester aroma of ‘Nanguo’ pears was effectively improved by MeJA during normal temperature shelf life. In addition, the expression of PuERS1, PuETR1, PuEIN4, PuEIN2 and PuERF1 in MeJA‐treated fruits were obviously increased. Therefore, we infer that the influence of MeJA on production of aroma‐related esters in ‘Nanguo’ pears is closely connected with ethylene biosynthesis and signal transduction, namely increase activity of ACS and ACO, and upregulation of the expression level of PuACS1, PuACO1, PuERS1, PuETR1, PuEIN2, PuEIN4 and PuERF1.

Ethylene-Induced Hydrogen Sulfide Negatively Regulates Ethylene Biosynthesis by Persulfidation of ACO in Tomato Under Osmotic Stress.

A number of recent studies identified hydrogen sulfide (H2S) as an important signal in plant development and adaptation to environmental stress. H2S has been proven to participate in ethylene-induced stomatal closure, but how the signaling pathways of H2S and ethylene interact is still unclear. Here, we reveal how H2S controls the feedback-regulation of ethylene biosynthesis in tomato (Solanum lycopersicum) under osmotic stress. We found that ethylene induced the production of H2S in guard cells. The supply of hypotaurine (HT; a H2S scavenger) or DL-pro-pargylglycine (PAG; a synthetic inhibitor of H2S) removed the effect of ethylene or osmotic stress on stomatal closure. This suggests that ethylene-induced H2S is a downstream component of osmotic stress signaling, which is required for ethylene-induced stomatal closure under osmotic stress. We further found that H2S inhibited ethylene synthesis through inhibiting the activity of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidases (ACOs) by persulfidation. A modified biotin-switch method (MBST) showed that H2S can induce persulfidation of LeACO1 and LeACO2 in a dose-dependent manner, and that persulfidation inhibits the activity of LeACO1 and LeACO2. We also found that LeACO1 is persulfidated at cysteine 60. These data suggested that ethylene-induced H2S negatively regulates ethylene biosynthesis by persulfidation of LeACOs. In addition, H2S was also found to inhibit the expression of LeACO genes. The results provide insight on the general mode of action of H2S and contribute to a better understanding of a plant’s response to osmotic stress.

LeMAPK4 participated in cold‐induced ethylene production in tomato fruit

Mitogen-activated protein kinase (MAPK, EC 2.7.11.24) cascade from several plant species has been shown to be activated during response to abiotic stress. Ethylene plays an important role in fruit tolerance to environmental stress. However, the mechanisms by which MAPK regulates defence systems in fruit and the relationship between MAPK and ethylene remain to be determined. MAPK inhibitor significantly decreased the chilling tolerance of tomato (Lycopersicon esculentum cv. Lichun) fruit during cold storage. Moreover, decreases in ethylene content, LeACS2 expression and activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS, EC 4.4.1.14) and ACC oxidase (ACO, EC 1.14.17.4) due to MAPK inhibitor occurred within 24 h after cold treatment. Upon treatment with cold and ethephon, the ethylene content, activities of ACS and ACO and expression of LeACS2, LeACO1 and LeMAPK4 increased. The results showed the regulation of MAPK in ethylene biosynthesis to protect tomato fruit from cold stress. In addition, the participation of LeMAPK4 in cold-induced ethylene biosynthesis in tomato fruit was indicated.

The regulation mode of RIN transcription factor involved in ethylene biosynthesis in tomato fruit

LE-RIN encodes the RIN (Ripening Inhibitor) transcription factor belonging to the MADS (Mcm1, Agamous, Deficiens, Srf) box family and regulates tomato ripening. The RIN transcription factor plays an indispensable role in ethylene biosynthesis. In the study, we respectively evaluated gene expressions and enzymatic activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS) and ACC oxidase (ACO) and ethylene production to understand the transcriptional regulation of RIN transcription factor in ethylene biosynthesis. RIN transcription factor generates strong or weak induction of the expression of LE-ACS2, LE-ACS4 and LE-ACO1 associated with ethylene biosynthesis. Exogenous ethylene could positively affect gene expression of mature green AC tomato fruit compared with the control, including LE-ACS2, LE-ACO1 and LE-ACO4. However, LE-ACS6 expression was negatively affected by RIN transcription factor and high ethylene production. Accordingly, the activities of ACC synthase and ACC oxidase and ethylene production were also changed. RIN transcription factor has an impact upon ethylene biosynthesis via regulating transcription of LE-ACS2, LE-ACS4, LE-ACO1 and LE-ACS6. These results will help to further clarify the mechanism of tomato fruit development and ripening, and to maintain quality and prolong shelf life of tomato fruit.

Methyl jasmonate plays a role in fruit ripening of ‘Pajaro’ strawberry through stimulation of ethylene biosynthesis

The role of methyl jasmonate (MJ) in strawberry ( Fragaria × ananassa Duch. cv Pajaro) fruit ripening was investigated by monitoring its endogenous concentrations in fruit at various stages of development and the effects of exogenously applied MJ at these stages on ethylene biosynthesis. The concentration of endogenous trans-MJ was significantly higher in the white fruit (31.7–162.2 ng g −1) and decreased sharply in half and fully ripe fruit. Higher concentrations of endogenous trans-MJ at the white stage of strawberry fruit development followed by a decline during fruit ripening indicate that MJ may play an important role in modulating fruit ripening. Significantly increased ethylene production was measured in the fruit when MJ was applied at white, half ripe and at fully ripe stage. The application of MJ (50 μM) resulted in significantly highest ethylene production and increased activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase as compared to all other treatments. The effect of exogenously applied MJ on ethylene production, ACC synthase and ACC oxidase activities was dependent on concentration of MJ applied and on fruit developmental stage. In conclusion, MJ in strawberry modulates fruit ripening, as its concentration is higher in white fruit and is declined with the progression of ripening and exogenous application of MJ increases ethylene production, activities of ACC oxidase and ACC synthase depending upon the concentration of MJ applied and fruit developmental stage.

Effects of postharvest ethanol vapor treatment on ethylene responsiveness in broccoli

Broccoli ( Brassica oleracea L. Italica Group) senesces very rapidly at room temperature after harvest. Ethanol vapor treatment with ethanol pads inhibits ethylene production and prolongs the shelf-life of harvested broccoli. The effects of postharvest ethanol vapor treatment on ethylene responsiveness in broccoli were investigated to clarify the mechanism of the inhibition of senescence with ethanol treatment and develop applications for ethanol pads. Broccoli branchlets were packed in a perforated polyethylene bag with or without ethanol pads and were continuously exposed to ethylene or not at 20 °C in darkness. Exogenous ethylene accelerated the yellowing of florets and stimulated ethylene and respiration climacteric patterns. These ethylene responses were inhibited by ethanol vapor treatment. Stimulation of the activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase and induction of the expression of BO-ACO1, BO-ACO2, and BO-ACS1 by exogenous ethylene were suppressed by ethanol vapor treatment. These results show that postharvest ethanol vapor treatment inhibits the senescence of harvested broccoli through the suppression of ethylene responsiveness as well as ethylene biosynthesis.

ACTIVITIES OF ?-GALACTOSIDASE AND ?-L-ARABINOFURANOSIDASE, ETHYLENE BIOSYNTHETIC ENZYMES DURING PEACH RIPENING AND SOFTENING

A study was conducted to determine changes in firmness, ethylene and ethylene biosynthetic enzymes, and the activities of β-galactosidase (β-GAL) and a-L-arabinofuranosidase (a-AF) during peach ripening and softening. The activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, ACC oxidase and polygalacturonase increased in parallel with ethylene production and declined in firmness during peach ripening, and they appeared at maximum simultaneously at maturity IV. β-GAL activity was high in unripe peach fruit and it experienced an overall decline during peach ripening. While α-AF activity changed placidly at the initial stage (maturity I-III), after that it experienced a rapid increasing stage. The preliminary result indicated that β-GAL and α-AF, as well as ethylene biosynthetic enzymes, may be involved in the ripening and softening of peach fruit.

Differential expression of genes involved in the biosynthesis and perception of ethylene during ripening of passion fruit (Passiflora edulis Sims).

An increase in the enzyme activity of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase induces the evolution of ethylene during the ripening of passion fruit. A much higher level of ethylene is produced in arils than in seeds or peels during ripening. The pattern of expression of two ACC synthase genes (PE-ACS1 and PE-ACS2), one ACC oxidase gene (PE-ACO1), and two ethylene receptor genes (PE-ETR1 and PE-ERS1) revealed that the expression of these genes is differentially regulated. Expression of PE-ACS1 and PE-ACO1 was enhanced during ripening and after ethylene treatment. However, prominent expression of PE-ACS1 was delayed compared to that of PE-ACO1. Much larger quantities of PE-ACS1 mRNA and PE-ACO1 mRNA were seen in arils than in seeds; this corresponds well with an increase in the amount of ethylene produced by the plant tissue itself. The level of PE-ACS2 mRNA was detectable in arils of the preclimacteric fruit, although it decreased during ripening. These results suggest that expression of PE-ACS1 and PE-ACO1 is required to increase the activity of ethylene biosynthetic enzymes during ripening. The level of expression of PE-ETR1 and PE-ERS1 did not significantly change over the course of ripening; however, the mRNA levels of PE-ETR1 and PE-ERS1 were much higher in arils than in seeds.

Diurnal Fluctuations in Ethylene Formation in Chenopodium rubrum.

Ethylene formation was studied in 5- to 6-d-old Chenopodium rubrum seedlings under the following light regimes: continuous light (CL), continuous darkness (CD), and alternating light/darkness (12 h of each). No significant regular oscillations in ethylene formation were found in either the CL or CD groups. In the light/dark regime, pronounced diurnal fluctuations in ethylene formation were observed. Activity of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase was transiently increased on transfer from light to dark and vice versa. In CL, ACC oxidase activity did not change significantly, whereas in CD, it decreased continuously after the initial increase. The in vivo levels of ACC and N-malonyl-ACC (MACC) were constant for the first few hours of darkness, then decreased dramatically, but increased again in the light. In constant darkness, the level of ACC displayed endogenous rhythm, with minimum values at h 12 and 44, and a maximum value at h 32 to 36. The level of MACC in both shoots and roots decreased in the CD group until h 12, and then remained constant until h 30 before decreasing continuously. We conclude that the photoperiodic regime affects both ACC and MACC levels, as well as the conversion of ACC to ethylene. Correlation of the described changes in ethylene formation to photoperiodic flower induction is discussed.

Ethylene Biosynthesis during Aerenchyma Formation in Roots of Maize Subjected to Mechanical Impedance and Hypoxia.

Germinated maize (Zea mays L.) seedlings were enclosed in modified triaxial cells in an artificial substrate and exposed to oxygen deficiency stress (4% oxygen, hypoxia) or to mechanical resistance to elongation growth (mechanical impedance) achieved by external pressure on the artificial substrate, or to both hypoxia and impedance simultaneously. Compared with controls, seedlings that received either hypoxia or mechanical impedance exhibited increased rates of ethylene evolution, greater activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, ACC oxidase, and cellulase, and more cell death and aerenchyma formation in the root cortex. Effects of hypoxia plus mechanical impedance were strongly synergistic on ethylene evolution and ACC synthase activity; cellulase activity, ACC oxidase activity, or aerenchyma formation did not exhibit this synergism. In addition, the lag between the onset of stress and increases in both ACC synthase activity and ethylene production was shortened by 2 to 3 h when mechanical impedance or impedance plus hypoxia was applied compared with hypoxia alone. The synergistic effects of hypoxia and mechanical impedance and the earlier responses to mechanical impedance than to hypoxia suggest that different mechanisms are involved in the promotive effects of these stresses on maize root ethylene biosynthesis.

高濃度炭酸ガスがモモおよびトマト果実のエチレン生合成に及ぼす影響

Ethylene production, oxygen uptake, the activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase in vivo and the contents of ACC and 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC) were determined in peach and tomato fruits held in carbon dioxide-enriched atmosphere. Ethylene production in peaches decreased to a trace level with 60% carbon dioxide and in tomatoes to 50% of the initial level. The ethylene production rates in both fruits reverted to the initial level when the fruits were transferred back to air. Oxygen uptake in both fruits was markedly inhibited during carbon dioxide exposure. In vivo activities of ACC oxidase and ACC synthase in both fruits were also inhibited during carbon dioxide exposure. ACC content in peaches held in carbon dioxide-enriched atmosphere decreased but it increased in tomatoes. The level of MACC in peaches was constant during carbon dioxide treatment, whereas that in tomatoes slightly increased. These results indicate that inhibition in ethylene production by carbon dioxide may be mediated mainly by reduced conversion of ACC to ethylene in tomatoes, whereas in peaches, the inhibition is attributed to both reduced conversion of S-adenosylmethionine to ACC and ACC to ethylene.

Inhibition of auxin-induced ethylene production in cucumber fruit discs by carbon dioxide

The induction of ethylene biosynthesis by indole-3-acetic acid (IAA) and its regulation by CO 2 was examined in cucumber ( Cucumis sativus L., var. Sharp-1) fruit discs. Treatment of discs with IAA significantly stimulated ethylene production and the extent depended on IAA concentration upto 1 mM. The increase in IAA-induced ethylene production was accompanied by increase in the activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ACC oxidase (also known as ethylene-forming enzyme) and a massive accumulation of ACC and 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC). The induction of ethylene production by IAA was inhibited by treatment with CO 2 . The extent of inhibition was dependent upon the concentration of CO 2 . Carbon dioxide inhibited IAA-induced ethylene biosynthesis by suppressing ACC synthase and ACC oxidase activities. Additionally, CO 2 inhibited ACC conjugation into MACC. The results indicate that inhibition of ethylene production by CO 2 in cucumber fruit discs following IAA treatment is due to inhibition of both ACC synthesis and ACC oxidation.

Anaerobiosis and plant growth hormones induce two genes encoding 1-aminocyclopropane-1-carboxylate synthase in rice (Oryza sativa L.).

The plant hormone ethylene is believed to be responsible for the ability of rice to grow in the deepwater regions of Southeast Asia. Ethylene production is induced by hypoxia, which is caused by flooding, because of enhanced activity of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, the key enzyme in the ethylene biosynthetic pathway. We have cloned three divergent members, (OS-ACS1, OS-ACS2, and OS-ACS3), of a multigene family encoding ACC synthase in rice. OS-ACS1 resides on chromosome 3 and OS-ACS3 on chromosome 5 in the rice genome. The OS-ACS1 and OS-ACS3 genes are induced by anaerobiosis and indoleacetic acid (IAA) + benzyladenine (BA) + LiCl treatment. The anaerobic induction is differential and tissue specific; OS-ACS1 is induced in the shoots, whereas OS-ACS3 is induced in the roots. These inductions are insensitive to protein synthesis inhibitors, suggesting that they are primary responses to the inducers. All three genes are actually induced when protein synthesis is inhibited, indicating that they may be under negative control or that their mRNAs are unstable. The OS-ACS1 gene was structurally characterized, and the function of its encoded protein (M(r) = 53 112 Da, pI 8.2) was confirmed by expression experiments in Escherichia coli. The protein contains all eleven invariant amino acid residues that are conserved between aminotransferases and ACC synthases cloned from various dicotyledonous plants. The amino acid sequence shares significant identity to other ACC synthases (69-34%) and is more similar to sequences in other plant species (69% with the tomato LE-ACS3) than to other rice ACC synthases (50-44%). The data suggest that the extraordinary degree of divergence among ACC synthase isoenzymes within each species arose early in plant evolution and before the divergence of monocotyledonous and dicotyledonous plants.

Turnover of 1-Aminocyclopropane-1-Carboxylic Acid Synthase Protein in Wounded Tomato Fruit Tissue

Ethylene production in plant tissues declines rapidly following induction, and this decline is due to a rapid decrease in the activity of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, a key enzyme in ethylene biosynthesis. To study the nature of the rapid turnover of ACC synthase in vivo, proteins in wounded ripening tomato (Lycopersicon esculentum) fruit discs were radiolabeled with [(35)S]methionine, followed by a chase with nonradioactive methionine. Periodically, the radioactive ACC synthase was isolated with an immunoaffinity gel and analyzed. ACC synthase protein decayed rapidly in vivo with an apparent half-life of about 58 min. This value for protein turnover in vivo is similar to that previously reported for activity half-life in vivo and substrate-dependent enzyme inactivation in vitro. Carbonylcyanide-m-chlorophenylhydrazone and 2,4-dinitrophenol, potent uncouplers of oxidative phosphorylation, strongly inhibited the rapid decay of ACC synthase protein in the tissue. Degradation of this enzyme protein was moderately inhibited by the administration of aminooxyacetic acid, a competitive inhibitor of ACC synthase with respect to its substrate S-adenosyl-l-methionine, alpha,alpha'-dipyridyl, and phenylmethanesulfonyl fluoride or leupeptin, serine protease inhibitors. These results support the notion that the substrate S-adenosyl-l-methionine participates in the rapid inactivation of the enzyme in vivo and suggest that some ATP-dependent processes, such as the ubiquitin-requiring pathway, are involved in the degradation of ACC synthase proteins.

Wound-induced ethylene synthesis and its involvement in enzyme induction in mesocarp tissue of Cucurbita maxima

Abstract The activity of peroxidase in mesocarp tissue of Cucurbita maxima was rapidly increased after wounding. The increase in peroxidase activity was preceded by increased ethylene production. The induction of peroxidase activity was strongly suppressed by the application of 2,5-norbornadiene (NBD) and aminoethoxyvinylglycine (AVG) to excised discs, indicating that endogenous ethylene produced in response to wounding may have promoted the induction of peroxidase. Raised activities of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and phenylalanine ammonia-lyase (PAL) were noted prior to increased peroxidase activity. Although no significant increases in soluble phenolics, such as chlorogenic acid, were found in the wounded mesocarp tissue, lignin formation was clearly enhanced by wounding along with the increased level of ethylene production and the enhanced levels of PAL and peroxidase activities. ACC synthase and PAL induced by wounding were observed to be located predominantly in the upper and adjacent 0.5 mm of the cut surface, while peroxidase activity was found to exist deep inside the tissue.