ACC Levels Research Articles

Effects of matriconditioning on onion seed germination, seedling emergence and associated physical and metabolic events

The effect of matriconditioning, the physiological presowing seed technique, using Micro-Cel E on Allium cepa L. cv. Czerniakowska seed quality was studied. Several ratios of seeds, carrier, water and time of priming were tested. The most effective treatment for improving onion seed germination at most tested temperatures was priming to a ratio of 2 g seed:1 g Micro-Cel:3 g water for 5 days in light at 15 °C. Matriconditioning greatly improved the germination and emergence percentage, seedling fresh and dry weight and reduced electrolyte leakage compared to that of untreated seeds; this beneficial effect was especially evident at suboptimal temperatures. Matriconditioning improved the germinability of aged seeds, the effect being more pronounced in the more aged seeds. No significant differences in ethylene production by primed and non-primed seeds were observed in the absence of its precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), but its presence during imbibition caused an increase in ethylene production; an enhanced activity of in vivo ACC oxidase in Allium cepa matriconditioned seeds in comparison to untreated seeds, indicates that the endogenous level of ACC is a limiting factor of ethylene production. Likewise, the activity of ACC oxidase isolated from matriconditioned seeds was higher than that from untreated seeds. Higher endo-β-mannanase and total dehydrogenase activities were observed in primed air-dried seeds in comparing to non-primed seeds.

Cold-induced ethylene biosynthesis is differentially regulated in peel and pulp tissues of ‘Granny Smith’ apple fruit

Abstract Ethylene biosynthesis and endogenous abscisic acid (ABA) concentrations were examined in commercially mature ‘Granny Smith’ apples during and following chilling exposure, in order to study the mechanism(s) leading to induction of ethylene biosynthesis in chilled fruit upon rewarming. The effects of exogenous ABA and ethylene during exposure to low temperature were also tested to assess the role of both growth regulators in the onset of increased ethylene biosynthesis upon removal from cold storage. Ethylene production rates, ACC oxidase (ACO) activity, ACC levels, presence of both ACO and ripening-related ACC synthase (ACS) proteins and endogenous ABA concentrations were monitored in both peel and pulp of fruit, based on previous results showing noticeable differences in maturation and ripening of both tissues in ‘Granny Smith’ apples. Remarkable differences were observed in the regulation of ethylene biosynthesis in peel and pulp of ‘Granny Smith’ apple fruit. ACO and ripening-related ACS were found to respond differentially to chilling and exogenous ethylene or ABA. It is suggested that increased endogenous ABA levels in the peel tissue might play a major role in cold-induced ethylene biosynthesis upon rewarming. This hypothesis would also imply a significant role for the peel tissue in climacteric ethylene biosynthesis.

Brassinosteroids affect ethylene production in the primary roots of maize (Zea mays L.)

To better understand the physiological roles of brassinosteroids (BRs) in the primary roots of maize, we examined their effect on ethylene production. Exogenously applied brassinolide (BL; 10-9 to 10-7 M) incrementally increased the level ethylene in a dose-dependent manner. This BL-induced production was enhanced in the presence of IAA, thereby implying a synergistic effect between BR and IAA. At 10-7 M BL, the level of free ACC was increased, but that of conjugated ACC was diminished. Moreover, greater concentrations of BL proportionally increased ACC oxidase activity. In contrast, higher levels of IAA increased the endogenous content of conjugated ACC as well as ACC synthase activity. Based on these results, we conclude that BR activates ethylene production mainly via ACC oxidase, and interacts with IAA to produce ethylene. However, the functional site for ethylene production is different for each hormone.

Effect of drought and high solar radiation on 1-aminocyclopropane-1-carboxylic acid and abscisic acid concentrations in Rosmarinus officinalis plants.

The endogenous concentrations of ACC and ABA were measured, at predawn and at maximum solar radiation, during a summer drought, and recovery after autumn rainfalls, in rosemary (Rosmarinus officinalis L.), a drought-tolerant species, growing under Mediterranean field conditions. During the summer, plants were subjected to both water deficit and high solar radiation. Plants showed severe reductions in shoot water potential to -3 MPa, which were associated with drastic stomatal closure (73%), a decrease in net photosynthesis, reaching almost zero, and a severe chlorophyll loss (74%). Despite the severity of the stress, plants recovered after the autumn rainfalls. The concentration of ACC was not enhanced by drought, and at predawn these concentrations remained constant at approximately 600 pmol ACC-1 DW throughout the experiment. Thus, ethylene did not regulate the response of rosemary to drought. However, a sharp increase in ACC levels between predawn and midday was observed. This increase was positively correlated to the intensity of the incident solar radiation. ACC levels recorded in June at midday reached 16 000 pmol g DW and in October values of 1000 pmol g-1 DW were observed. In contrast, in drought-stressed plants predawn concentrations of ABA were up to 130-fold those of recovered plants, and the levels of ABA scored at midday were double of those scored at predawn. In conclusion, although drought-stressed rosemary plants showed a relatively moderate ABA accumulation (approximately 500 pmol g-1 DW#, at predawn), it seems to be an essential factor for the regulation of the plant response to stress, thereby enabling a rapid recovery after stress release, although other mechanisms can not be excluded. As drought stress did not induce ACC accumulation, it was concluded that ethylene production was not a major factor in the drought stress resistance of rosemary plants. The increased ACC and ABA concentrations at midday were correlated with day length and light intensity and not with the water status of the plant.

Wound-induced ethylene synthesis in stem tissue of harvested broccoli and its effect on senescence and ethylene synthesis in broccoli florets

Abstract Broccoli ( Brassica oleracea , var. italica ) florets (flower buds) senesced rapidly after harvest at ambient temperatures. ACC (1-aminocyclopropane-1-carboxylic acid) synthase (ACS) was induced rapidly in the cut surface of stem tissue in the first 2 mm thick and the basal portions of curds soon after harvest, leading to an accumulation of ACC. The abundance of one ACS mRNA (BO-ACS1) increased in the first layer, the inner layer of stem (2–4 mm, second layer), and the basal portion of curds, while the transcripts for another (BO-ACS2) increased only in the first layer. Conjugated ACC (malonyl ACC, MACC) levels increased in all portions as senescence progressed. In florets, ACC synthase activity and BO-ACS1 transcripts were detected with no significant changes observed during senescence. ACC levels in florets stayed low throughout the experimental period, whereas MACC levels were much higher than those of ACC. The marked rise in ACC oxidase (ACO) activity in florets was detected almost in parallel with a significant increase in ethylene production. The abundance of ACO transcripts (BO-ACO1 and BO-ACO2) increased concurrently with the rise in ACC oxidase activity. These findings suggest that ACC and ethylene synthesized in the stem in response to wounding may have involved the enhanced activity of ACC oxidase and increased abundance of its transcripts in florets.

The effect of AOA on ethylene and polyamine metabolism during early phases of somatic embryogenesis in Medicago sativa.

Changes in the levels of ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC) and polyamines were simultaneously investigated during the early phases of alfalfa somatic embryogenesis. These included the period of induction and subculture of callus, and 3- and 7-day suspension cultures for the induction of somatic embryogenesis. The polyamines contained in the embryogenic callus were found to include putrescine (Put), spermidine (Spd) and spermine (Spm), but the level of Spm was much less than that of Put and Spd. There was a dramatic increase in MACC after induction of embryogenesis, and ACC levels were lower in somatic embryos than in embryogenic callus. Induction of embryogenesis for 3 days increased the levels of ACC and polyamines to a maximum level, and these then reduced as the embryogenesis proceeded. The ratios of Put/Spd and ACC/MACC were decreased during the induction. This indicated that both high levels of ACC and polyamines might be a prerequisite for early differentiation during the induction of the embryogenesis. Thus, there appears not to be competition between polyamine biosynthesis and ethylene biosynthesis at least during the induction of somatic embryogenesis, because both the polyamines and ACC were simultaneously increased during the induction period. Conversion of ACC into MACC and the maintenance of a relatively high level of polyamines, especially Spd, appear to be important for further development of the embryos. When aminooxylvinylglycine (AOA) was added at the initiation of the callus subculture, it had no significant effect on the callus growth, the ethylene production and ACC level of the callus. However, AOA increased the numbers of the embryos accompanying an increase in Spd level and S-adenosylmethionine decarboxylase (SAMDC) activity. Thus, the AOA effect could be associated with Spd increase rather than with the effect of ethylene biosynthesis.

The last step of the ethylene biosynthesis pathway in turnip tops (Brassica rapa) seeds: Alterations related to development and germination and its inhibition during desiccation.

The involvement of ethylene in zygotic embryogenesis is a little known aspect of the growth and development in higher plants. In the present work, we study the alterations of the last step of the ethylene biosynthesis pathway during the formation period of turnip tops (Brassica rapa cv. Rapa) seeds and its repercussions in the germination process and post-germinative growth. For this, we chose 11 different phases of silique development, the first being the recently fertilized pistil and the last being the silique just prior to its dehiscence (ca. 2 months post-anthesis). In the 11 phases, ethylene production was detected in both whole silique (with or without seeds) and in the seeds enclosed by the silique wall. The levels of ACC, ACO and ethylene production proved high in seeds belonging to: (1) the pod in the very early phases, when the seeds were growing but without photosynthetic competence; (2) the silique at maximum growth, in which the seeds will initiate desiccation and loss of photosynthetic activity. During the phases prior to dehiscence, there was a marked inhibition in the last step of the ethylene biosynthesis pathway. In viable dry seeds, no ACO activity was detected and the ACC levels were 4-fold lower than at the onset of the silique senescence. Germination brings about a net synthesis of ACC with respect of the stores dry seed. This fact, together with other results presented in this work, point towards, as in other seeds, a dependence of ethylene synthesis for radicle emergence. The possible role played by the silique wall in the control of ethylene biosynthesis during zygotic embryogenesis, as well as the participation of ethylene as a hormonal signal in the triggering of seed desiccation in Brassica rapa cv. Rapa, are discussed in depth.

Brassinosteroid-induced exaggerated growth in hydroponically grown Arabidopsis plants.

The effects of root application of brassinolide (BL) on the growth and development of Arabidopsis plants (Arabidopsis thaliana ecotype Columbia [L.] Heynh) were evaluated. Initially, all leaves were evaluated on plants 18, 22, 26 and 29 days old. The younger leaves were found to exhibit maximal petiole elongation and upward leaf bending in response to BL treatment. Therefore, based on these results leaves 6, 7 and 8 on 22-24-day-old plants were selected for all subsequent studies. Elongation along the length of the petiole in response to BL treatment was uniform with the exception of an approximately 4 mm region next to the leaf where upward curvature was observed. Both BL and 24-epibrassinolide (24-epiBL) were evaluated, with BL being more effective at lower concentrations than 24-epiBL. The exaggerated growth induced by 0.1 µM BL was not observed in plants treated with 1 000-fold higher concentrations of GA3, IAA, NAA or 2,4-D (100 µM). In addition, no exaggerated growth effects were observed when plants were treated with 200 ppm ethylene or 1 mM ACC. All treatments with BL, NAA, 2,4-D, IAA or ACC promoted ethylene and ACC production in wild type Arabidopsis plants, but only BL triggered exaggerated plant growth. BL also promoted exaggerated growth and elevated levels of ACC and ethylene in the ethylene insensitive mutant etr1-3, showing that the effect of BR on growth is independent of ethylene. This work provides evidence that BR-induced exaggerated growth of Arabidopsis plants is independent of gibberellins, auxins and ethylene.

Levels of ACC and related compounds in exudate and extracts of canola seeds treated with ACC deaminase-containing plant growth-promoting bacteria.

It was previously proposed that plant growth-promoting bacteria that possess 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase could utilize ACC that is present in the exudate of germinating canola seeds. The uptake and cleavage of ACC by these bacteria would lower the level of ACC, and thus ethylene within the plant, and reduce the extent of its inhibition on root elongation. To test part of the above mentioned model, ACC levels were monitored in canola seed tissues and exudate during germination. Lower amounts of ACC were present in the exudate and tissues of seeds treated with the plant growth-promoting bacterium Enterobacter cloacae CAL3, than in control seeds treated with MgSO4. The ACC-related compounds, alpha- and gamma-aminobutyric acids, both known to stimulate ethylene production, were also measured in the canola seed exudate and tissues. Approximately the same levels of alpha-aminobutyric acid were present in the exudates of the bacterium-treated seeds and the control seeds, but the amount of alpha-aminobutyric acid was lower in the tissues of the bacterium-treated seeds than in the control seeds. Smaller quantities of gamma-aminobutyric acid were seen in both the exudate and tissues of the E. cloacae CAL3-treated seeds than in the control seeds.

Levels of ACC and related compounds in exudate and extracts of canola seeds treated with ACC deaminase-containing plant growth-promoting bacteria

Levels of ACC and related compounds in exudate and extracts of canola seeds treated with ACC deaminase-containing plant growth-promoting bacteria

Determination of 1-aminocycopropane-1-carboxylic acid (ACC) to assess the effects of ACC deaminase-containing bacteria on roots of canola seedlings.

Previously, it was proposed that plant growth-promoting bacteria that possess the enzyme, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, can reduce the amount of ethylene produced by a plant and thereby promote root elongation. To test this model, canola seeds were imbibed in the presence of the chemical ethylene inhibitor, 2-aminoethoxyvinyl glycine (AVG), various strains of plant growth-promoting bacteria, and a psychrophilic bacterium containing an ACC deaminase gene on a broad host range plasmid. The extent of root elongation and levels of ACC, the immediate precursor of ethylene, were measured in the canola seedling roots. A modification of the Waters AccQ.Tag Amino Acid Analysis Method was used to quantify ACC in the root extracts. It was found that, in the presence of the ethylene inhibitor, AVG, or any one of several ACC deaminase-containing strains of bacteria, the growth of canola seedling roots was enhanced and the ACC levels in these roots were lowered.

Auxin-induced ethylene triggers abscisic acid biosynthesis and growth inhibition.

The growth-inhibiting effects of indole-3-acetic acid (IAA) at high concentration and the synthetic auxins 7-chloro-3-methyl-8-quinolinecarboxylic acid (quinmerac), 2-methoxy-3,6-dichlorobenzoic acid (dicamba), 4-amino-3,6, 6-trichloropicolinic acid (picloram), and naphthalene acetic acid, were investigated in cleavers (Galium aparine). When plants were root treated with 0.5 mM IAA, shoot epinasty and inhibition of root and shoot growth developed during 24 h. Concomitantly, 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity, and ACC and ethylene production were transiently stimulated in the shoot tissue within 2 h, followed by increases in immunoreactive (+)-abscisic acid (ABA) and its precursor xanthoxal (xanthoxin) after 5 h. After 24 h of treatment, levels of xanthoxal and ABA were elevated up to 2- and 24-fold, relative to control, respectively. In plants treated with IAA, 7-chloro-3-methyl-8-quinolinecarboxylic acid, naphthalene acetic acid, 2-methoxy-3,6-dichlorobenzoic acid, and 4-amino-3,6,6-trichloropicolinic acid, levels of ethylene, ACC, and ABA increased in close correlation with inhibition of shoot growth. Aminoethoxyvinyl-glycine and cobalt ions, which inhibit ethylene synthesis, decreased ABA accumulation and growth inhibition, whereas the ethylene-releasing ethephon promoted ABA levels and growth inhibition. In accordance, tomato mutants defective in ethylene perception (never ripe) did not produce the xanthoxal and ABA increases and growth inhibition induced by auxins in wild-type plants. This suggests that auxin-stimulated ethylene triggers ABA accumulation and the consequent growth inhibition. Reduced catabolism most probably did not contribute to ABA increase, as indicated by immunoanalyses of ABA degradation and conjugation products in shoot tissue and by pulse experiments with [(3)H]-ABA in cell suspensions of G. aparine. In contrast, studies using inhibitors of ABA biosynthesis (fluridone, naproxen, and tungstate), ABA-deficient tomato mutants (notabilis, flacca, and sitiens), and quantification of xanthophylls indicate that ABA biosynthesis is influenced, probably through stimulated cleavage of xanthophylls to xanthoxal in shoot tissue.

Ethylene feedback mechanisms in tomato and strawberry fruit tissues in relation to fruit ripening and climacteric patterns

Exposing pericarp tissue excised from immature tomato fruit to 4.5 mmol l 1 C2H4 revealed a negative C2H4 feedback mechanism in relation to its biosynthesis since ACC concentration and C2H4 production by the tissue were reduced. An opposite trend (positive C2H4 feedback mechanism) was observed in pericarp tissue excised from fruit at the pink stage. At the mature-green stage however, tissue showed a transition from negative to positive C2H4 feedback mechanism with the onset of tissue ripening. In strawberry tissues excised from green, white and half-coloured fruits however, C2H4 application caused a short-term increase in C2H4 production followed by a sharp reduction to the control level along with a marked reduction in ACC levels. In both tomato and strawberry fruit tissues, C2H4 application significantly induced ACC oxidase (ACO) activity at all ripening stages, as measured by in vivo ACC conversion to C2H4. This strongly suggests that ACC synthesis is the limiting step in C2H4 autocatalysis and the only limiting step in C2H4 autoinhibition. In tomato pericarp tissues, C2H4 autoinhibition and autocatalysis caused by C2H4 application in immature and pink fruits, respectively, were eliminated when tissues were transferred to air and re-occurred when tissues were returned back to C2H4. These responses did not occur in all strawberry tissues due to the sharp reduction in C2H4 production with the time course of C2H4 application. Inhibiting C2H4 action with STS pretreatment inhibited both negative and positive C2H4 feedback mechanisms in both tomato and strawberry tissues indicating that C2H4 feedback mechanism is one sort of C2H4 action. In addition, only tomato fruit tissue showed significant increases in CO2 production with C2H4 application. In contrast to the nonclimacteric behaviour of strawberry fruit which exhibits only a negative C2H4 feedback mechanism, these data strongly suggest that the transition of the C2H4 feedback mechanism from negative to positive, which occurs in tomato fruit only with ripening initiation and progress, may be the reason behind the climacteric behaviour of tomato fruit. © 2000 Elsevier Science B.V. All rights reserved.

Kinetics of ethylene biosynthesis and its effects during maturation of white spruce somatic embryos

The objective of the current investigation was to study the role of ethylene in the maturation of white spruce (Picea glauca [Moench.] Voss) somatic embryos. This was carried out by examining the effects of (1) 1-aminocyclopropane-1-carboxylic acid (ACC), a direct precursor of ethylene in plant tissue, (2) silver nitrate (AgNO 3 ), an inhibitor of ethylene action, (3) α-aminooxyamino acid (AOA), a potent inhibitor of ethylene biosynthesis, and (4) enrichment with ethylene. Ethylene biosynthesis was biphasic and gradually increased during embryo development, whereas endogenous ACC and N-malonylaminocyclopropane-1-carboxylic acid (mACC) decreased. Addition of ACC or AOA to the culture medium increased or decreased, respectively, ethylene biosynthesis by altering endogenous ACC levels during the culture period. In contrast to AOA and AgNO 3 , ACC and ethylene enrichment significantly decreased the production of mature somatic embryos and increased the browning of the cultures. However, the structure of the shoot apex in mature cotyledonary stage embryos formed under ethylene enrichment was similar to that in control systems. This shows that a reduction in ethylene is beneficial to maturation of white spruce somatic embryos. This is further substantiated by the finding that the inhibitory effects of AOA were partially reversed by the addition of ethylene. The possible effects of the interaction between ethylene and polyamines on somatic embryo development are also discussed.

Ethylene promotes ethylene biosynthesis during pea seed germination by positive feedback regulation of 1-aminocyclo-propane-1-carboxylic acid oxidase.

Increased ethylene evolution accompanies seed germination of many species including Pisum sativum L., but only a little is known about the regulation of the ethylene biosynthetic pathway in different seed tissues. Biosynthesis of the direct ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), the expression of ACC oxidase (ACO), and ethylene production were investigated in the cotyledons and embryonic axis of germinating pea seeds. An early onset and sequential induction of ACC biosynthesis, accumulation of Ps-ACO1 mRNA and of ACO activity, and ethylene production were localized almost exclusively in the embryonic axis. Maximal levels of ACC, Ps-ACO1 mRNA, ACO enzyme activity and ethylene evolution were found when radicle emergence was just complete. Treatment of germinating seeds with ethylene alone or in combination with the inhibitor of ethylene action 2,5-norbornadiene showed that endogenous ethylene regulates its own biosynthesis through a positive feedback loop that enhances ACO expression. Accumulation of Ps-ACO1 mRNA and of ACO enzyme activity in the embryonic axis during the late phase of germination required ethylene, whereas Ps-ACS1 mRNA levels and overall ACC contents were not induced by ethylene treatment. Ethylene did not induce ACO in the embryonic axis during the early phase of germination. Ethylene-independent signalling pathways regulate the spatial and temporal pattern of ethylene biosynthesis, whereas the ethylene signalling pathway regulates high-level ACO expression in the embryonic axis, and thereby enhances ethylene evolution during seed germination.

The Mechanism of Quinclorac Selectivity in Grasses

The mechanism of selectivity of the auxin herbicide quinclorac was studied in susceptible and resistant biotypes of Echinochloa hispidula and E. crus-galli; in grass species of different susceptibility like Brachiaria platyphylla, Setaria viridis, E. colonum, and Digitaria sanguinalis; and in tolerant crop rice (Oryza sativa cv. Thaibonnet). No significant differences in uptake, translocation, or metabolism of quinclorac between resistant and sensitive grasses were found. Hence, the mechanism of selectivity is target-site-based. It has been demonstrated that cyanide, which accumulates as a coproduct during stimulation of ethylene biosynthesis, is the primary phytotoxic principle in the herbicidal mode of action of quinclorac in E. crus-galli (K. Grossmann and J. Kwiatkowski, 1995, Pestic. Biochem. Physiol. 51, 150). Following root treatment of plants at the third leaf stage with 100 M quinclorac in hydroponics, the reductions in shoot growth of plants were closely correlated with the stimulation of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity and with subsequent increases in endogenous concentrations of ACC and cyanide. When compared quinclorac with other auxin herbicides including quinmerac, α-naphthaleneacetic acid and dicamba, lower ACC and cyanide levels and correlated lower growth effects were found after treatment of D. sanguinalis. In quinclorac-resistant grass species and biotypes, ACC synthase activity was not induced and plants exhibited no significant changes in ACC and cyanide levels. Thus, the selective induction of ACC synthase activity, which ultimately leads to cyanide accumulation in the tissues of susceptible plants, plays the primary role for the selectivity of grasses toward quinclorac. This selectivity could be at the level of quinclorac perception or subsequent signal transduction via the auxin pathway leading to regulation of gene expression or posttran scriptional de novo enzyme synthesis. In rice, tolerance to quinclorac could be additionally favored by a higher β-cyanoalanine synthase activity, the main HCN-detoxifying enzyme.

Relation between Ethylene-producing Potential and Gene Expression of 1-Aminocyclopropane-1-carboxylic Acid synthase in Actinidia chinensis and A. deliciosa Fruits.

Large differences in gene expression of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, ACC contents, and ACC synthase activitiy were found in different tissues of fruit between members of two kiwifruit species, (cv) Actinidia chinensis ('Kui mi') and A. deliciosa ('Hayward'). ACC synthase mRNA accumulated mostly in the outer pericarp, slightly in the inner pericarp, and in a trace quantity in the columella of 'Hayward' fruit that produces much less ethylene than does 'Kui mi'. However, gene transcripts at significant levels exist in all sections of 'Kui mi' fruit which reflects a large potential to produce ethylene. ACC levels and ACC synthase activities were much higher in all the tissues of 'Kui mi' fruit than in 'Hayward' fruit, which indicates that these enzymes are the primary cause for the varietal difference in the ability to produce ethylene in kiwifruit.

Ethylene production, senescence and ethylene sensitivity of Dendrobium ‘Pompadour’ flowers following pollination

SummaryDendrobium ‘Pompadour’ flowers had a burst of ethylene production that peaked 9 h after pollination. Pollination increased 1-aminocyclopropane-1-carboxylic acid (ACC) content and ACC synthase activity. Ovary, lip and pedicel ACC levels and ACC synthase activity were many-fold greater than those of the petals and sepals following pollination. Aminooxyacetic acid (AOA) application to the stigma prior to pollination reduced ethylene production, ACC levels and ACC synthase activity. Ethylene production by pollinated orchid flowers, with ACC application, increased more rapidly than in nonpollinated orchid flowers with ACC application. Pollination induced a rise in ethylene production, and then premature senescence. The first sign of premature senescence was a downward curvature of orchid flowers accompanied by drooping of the petals and sepals. Both AOA and 2,5-norbornadiene (NBD) delayed premature senescence of pollinated orchid flowers, though AOA was the more effective. Exogenous ethylene induced premature senescence of orchid flowers similar to pollination and pollination increased the ethylene-sensitivity. AOA treatment did not alter ethylene sensitivity of pollinated orchid flowers.

Differential effects of low-temperature inhibition on the propylene induced autocatalysis of ethylene production, respiration and ripening of ‘Hayward’ kiwifruit

SummaryPrevious studies (Stavroulakis and Sfakiotakis, 1993) have shown an inhibition of propylene-induced ethylene production in kiwifruit below a critical temperature range of 11–14.8CC. The aim of this research was to identify the biochemical basis of this inhibition in kiwifruit below 11–14.8°C. ‘Hayward’ kiwifruit were treated with increasing propylene concentrations at 10 and 20°C. Ethylene biosynthesis pathways and fruit ripening were investigated. Kiwifruit at 20°C in ah started autocatalysis of ethylene production and ripened after 19 d with a concomitant increase in respiration. Ethylene production and the respiration rise appeared earlier with increased propylene concentrations. Ripening proceeded immediately after propylene treatment, while ethylene autocatalysis needed a lag period of 24#8212;72 h. The latter event was attributed to the delay found in the induction of 1-aminocyclopropane-l-carboxylate synthase (ACC synthase) activity and consequently to the delayed increase of 1-aminocyclopropane-l-carboxylic acid (ACC) content. In contrast propylene treatment induced 1-aminocyclopropane-l-carboxylate oxidase (ACC oxidase) activity with no lag period. Moreover, transcription of ACC synthase and ACC oxidase genes was active only in ethylene-producing kiwifruit at 20CC. In contrast, treatment at 10°C with propylene strongly inhibited ethylene production, which was attributed to the low activities of both ACC synthase and ACC oxidase as well as the low initial ACC level. Interestingly, fruit treated with propylene at 10°C appeared to be able to transcribe the ACC oxidase but not the ACC synthase gene. However, propylene induced ripening of that fruit almost as rapidly as in the propylene-treated fruit at 20CC. Respiration rate was increased together with propylene concentration. It is concluded that kiwifruit stored at 20°C behaves as a typical climacteric fruit, while at 10°C behaves like a non-climacteric fruit. We propose that the main reasons for the inhibition of the propylene induced (autocatalytic) ethylene production in kiwifruit at low temperature (≤io°C), are primarily the suppression of the propylene-induced ACC synthase gene expression and the possible post-transcriptional modification of ACC oxidase.

Chilling‐induced leaf abscission of Ixora coccinea plants. I. Induction by oxidative stress via increased sensitivity to ethylene

Exposing ixora (Ixora coccinea) plants to chilling temperatures (3–9°C for 3 days) resulted in increased leaf abscission, initiated 3 days after transfer to 20°C. Exposure to chilling also induced a 7‐fold increase in ethylene production rates of abscission zone (AZ) tissue during the initial 5 h after chilling. The ethylene burst resulted from the high levels of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) accumulated in the AZ during the chilling period. ACC levels following chilling decreased also due to enhanced conjugation to 1‐(malonylamino)cyclopropane‐1‐carboxylic acid (MACC). Treating plants prior to chilling with antioxidants, such as butylated hydroxyanisole (BHA), n‐propyl gallate (PG), and vitamin E, significantly reduced chilling‐induced leaf abscission. This effect was obtained despite the fact that ethylene production in the treated plants resembled that of chilled plants receiving no BHA. In addition, exposure of plants to ethylene (0.5–10 μl l−1) for 1–3 days significantly enhanced leaf abscission only when they had been pre‐chilled. These data imply that chilling‐induced leaf abscission was closely correlated with increased sensitivity of the AZ to ethylene rather than with the chilling‐induced ethylene burst. Based on the findings that the ethylene action inhibitor, 1‐methylcyclopropene (1‐MCP), and the antioxidant BHA inhibited both the chilling‐induced and the ethylene‐enhanced leaf abscission, it is concluded that: (1) although ethylene is essential for chilling‐induced abscission, it is not the triggering factor; (2) oxidative processes derived from the chilling stress seem to be the trigger of chilling‐induced leaf abscission, operating via increased sensitivity to ethylene.