Effect of 1-Aminocyclopropane-1-carboxylic acid and aminoethoxyvinylglycine on ethylene emanation and somatic embryogenesis from orchardgrass leaf cultures

Ethylene emanation rates were assessed from leaf tissues of an embryogenic seed plant (Cycle 0) and regeneration cycle plants selected for enhanced embryogenesis (Cycles I, II and IV). In all experiments, ethylene was assessed from the basal 1 cm portion of the innermost leaf. Ethylene emanation was five-fold higher in Cycle II and Cycle IV plants than in Cycle 0 and nonembryogenic (NE) seed plants. After two days culture on Schenk and Hildebrandt medium containing 30 M dicamba (SH-30), ethylene emanation from Cycle 0 and Cycle II leaf sections increased by 55-fold. Culture of leaf explants for 30 days on SH-30 containing 1 mM 1-aminocyclopropane-1-carboxylic acid (ACC) reduced the embryogenic response by 99%. Treatment of leaf explants with 1 mM aminoethoxyvinylglycine (AVG) reduced ethylene emanation but did not affect embryogenesis. The data indicate that ethylene mediated by ACC may hinder the embryogenic response from orchardgrass leaf cultures.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine     

Synergistic effect of ethylene inhibitors and putrescine on shoot regeneration from hypocotyl explants of Chinese radish (Raphanus sativus L. var. longipinnatus Bailey) in vitro

Summary The role of ethylene and putrescine on shoot regeneration from hypocotyl explants of Chinese radish (Raphanus sativus L. var. longipinnatus Bailey cv. Red Coat) was investigated. Explants were recalcitrant in culture, but exogenous application of ethylene inhibitor [20–30 M aminoethoxyvinylglycine (AVG) or AgNO₃] enhanced shoot regeneration of explants grown on medium supplemented with 2 mg/l N⁶-benzyladenine and 1 mg/l 1-naphthaleneacetic acid. The best regeneration occurred in the medium containing AgNO₃ in combination with AVG. Culture medium solidified with agarose in the presence of AgNO₃ but not AVG was also beneficial to shoot regeneration. Exogenous putrescine, 2-chloroethylphosphonic acid and 1-aminocyclopropane-1-carboxylate had no effect on shoot regeneration. However, regeneration was greatly promoted by 10–25 mM putrescine in combination with 30 M AgNO₃ or AVG. Explants with high regenerability grown in the presence of AgNO₃ or in combination with putrescine emanated high levels of ethylene throughout the 21-d culture period. By contrast, AVG or putrescine alone resulted in a decrease in ethylene production. For rooting of shoot cuttings, IAA and IBA at 1–5 mg/l were more effective than NAA.Abbreviations ACC 1-aminocyclopropane-1-carboxylate - AVG aminoethoxyvinylglycine - BA N⁶-benzyladenine - CEPA 2-chloroethylphosphonic acid - IAA indole-3-acetic acid - IBA indole-3-butyric acid - MS Murashige and Skoog (1962) medium - NAA 1-naphthaleneacetic acid - PAs polyamines - SAM S-adenosyl-L-methionine     

Role of polyamines in adventitious shoot morphogenesis from cotyledons of cucumber <Emphasis Type="Italic">in vitro</Emphasis>

The relationship between polyamines (PAs) metabolism and adventitious shoot morphogenesis from cotyledons of cucumber was investigated in vitro. The endogenous levels of free putrescine (Put) and spermidine (Spd) in the explants decreased sharply, whereas endogenous spermine (Spm) increased during adventitious shoot morphogenesis. The presence of 1–15 mM Put, 1–2 mM Spd, 0.05–1 mM Spm, 5–10 M aminoethoxyvinylglycine (AVG) or 5 M AVG together with 50 M 1-aminocyclopropane-1-carboxylic acid (ACC) in the regeneration medium could promote adventitious shoot formation. Conversely, 1–5 mM D-arginine (D-Arg) or 0.01–0.1 mM methylglyoxal bis-guganylhydrazone (MGBG) inhibited regeneration; and 0.005–0.05 mM ACC displayed little or no evident effects. The explants growing on medium containing 5 M AVG produced higher levels of free Put and Spm, and on medium containing 5 mM Put the explants responded similarly to the AVG-treated explants. However, the exogenous use of 1 mM D-Arg reduced the levels of Put, Spd and Spm, and 0.1 mM MGBG reduced the levels of free Spd and Spm. Moreover, although the explants cultured on medium containing Put and MGBG enhanced ethylene production, AVG and D-Arg inhibited ethylene biosynthesis. This study shows the PAs requirement for the formation of adventitious shoot from cotyledons of cucumber in vitro and the enhanced adventitious shoot morphogenesis may be associated with the elevated level of endogenous free Spm, albeit the promotive effect of PAs on adventitious shoot morphogenesis may not be related to ethylene metabolism.     

Role of polyamines on de novo shoot morphogenesis from cotyledons of Brassica campestris ssp. pekinensis (Lour) Olsson in vitro

Summary The promotive effect of ethylene inhibitors (Els), i.e. AgNO₃ and aminoethoxyvinylglycine (AVG) on de novo shoot regeneration from cultured cotyledonary explants of Brassica campestris ssp. pekinensis cv. Shantung in relation to polyamines (PAs) was investigated. The endogenous levels of free putrescine and spermidine in the explant decreased sharply after 1–3 days of culture, whereas endogenous spermine increased, irrespective of the absence or presence of Els. AgNO₃ at 30 M did not affect endogenous PAs during two weeks of culture. In contrast, explants grown on medium containing 5 M AVG produced higher levels of free putrescine and spermine which increased rapidly after three days and reached a peak at 10 days. An exogenous application of 5 mM putrescine also resulted in a similar surge of endogenous free spermine of the explant. More strikingly, shoot regeneration from explants grown in the presence of 1–20 mM putrescine, 0.1–2.5 mM spermidine, or 0.1–1 mM spermine was enhanced after three weeks of culture. However, exogenous PAs generally did not affect ethylene production, and endogenous levels of 1-aminocyclopropane-1-carboxylate (ACC) synthase activity and ACC of the explant. This study shows the PA requirement for shoot regeneration from cotyledons of B. campestris ssp. pekinensis in vitro, and also indicates that the promotive effect of PAs on regeneration may not be due to an inhibition of ethylene biosynthesis.Abbreviations PAs polyamines - AVG aminoethoxyvinylglycine - SAM S-adenosylmethionine - ACC 1-aminocyclopropane-1-carboxylate - Els ethylene inhibitors     

Regulation of Stem Abscission and Callus Growth in Shoot Explants of Sweet Orange [Citrus sinensis (L.) Osbeck]

Two-node explants from Sweet Orange cv. St Ives Valencia orangeshoots produced prolific callus and formed secondary abscissionzones within internodes when cultured in vitro with abscisicacid (ABA, 5 µM) or -naphthaleneacetic acid (NAA, 5 µM).Benzyladenine (BA, 1 µm) induced callus but had littleeffect on abscission. Secondary abscission zone formation wasassociated with ABA-induced and auxin-induced ethylene formation.Treatment of explants with inhibitors of ethylene synthesis[aminoethoxyvinyl glycine (AVG), Co²⁺, PO₄^3–] preventedformation of secondary abscission zones but had variable effectson callus formation. Newly made explants contained high concentrationsof endogenous ABA (up to 6000 ng g^–1 f.wt), as measuredby GC/MS/SIM. Long-term subculture of explants (two years) inmedia containing BA (1 µm) led to a reduction in endogenousABA level (40 ng g^–1 f. wt) and to loss of capacity toform extensive callus and secondary abscission zones. Citrus sinensis (L.) Osbeck cv. St Ives Valencia, sweet orange, secondary abscission zones, in vitro, ethylene, endogenous ABA, endogenous IAA     

Endogenous ethylene requirement for adventitious root induction and growth in tomato cotyledons and lavandin microcuttings in vitro

The role of ethylene in the formation of adventitious roots in vitro was studied in tomato (Lycopersicon esculentum Mill. cv. UC 105) cotyledons and lavandin (Lavandula officinalis Chaix × Lavandula latifolia microshoots. Both systems were able to form roots on hormone-free medium evolving low amounts of ethylene. The addition of 20–50 M indole-3-acetic acid (IAA) inhibited root formation in tomato cotyledons while increasing ethylene production. Naphthaleneacetic acid (NAA, 3 M) stimulated root number in lavandin explants and induced a transient rise in ethylene evolution. Enhanced ethylene levels via the endogenous precursors 1-aminocyclopropane-1-carboxylic acid (ACC, 25–50 M) drastically impaired root regeneration and growth in tomato. In lavandin, 10 M ACC stimulated ethylene production and significantly inhibited the rooting percentage and root growth. Conversely, ACC enhanced the root number in the presence of NAA only. Severe inhibition of rooting was also caused by ethylene reduction via biosynthetic inhibitors, aminoethoxyvinylglycine (AVG, 5–10 M) in tomato, and salicylic acid (SA, 100 M) in lavandin. A strict requirement of endogenous ethylene for adventitious root induction and growth is thus suggested.Abbreviations LS Linsmaier and Skoog medium - BA N⁶-benzyladenine - NAA 1-naphthaleneacetic acid - IAA Indole-3-acetic acid - AVG Aminoethoxyvinylglycine - SA Salicylic acid - ACC 1-aminocyclopropane-1-carboxylic acid     

Effect of l-aminocyclopropane-l-carboxylic acid,silver nitrate,and norbornadiene on plant regeneration from maize callus cultures

The effect of the ethylene antagonists norbornadiene and silver nitrate and the ethylene precursor l-aminocyclopropane-l-carboxylic acid (ACC) on Zea mays plant regeneration was studied. A 12-fold increase in plant regeneration, as measured by number of plants obtained per gram fresh weight from callus cultures of maize inbreds Pa91 and H99, was obtained by 250 M norbornadiene and 100 M silver nitrate treatments. An increase in amout of nonregenerable tissue and a 68% decrease in plant regeneration were associated with callus treated with 1 mM ACC. Ethylene emanation from 1 mM ACC treated callus reached a maximum of 170 nl g^–1 h^–1 after 3 days compared to 7 nl g^–1 h^–1 for the control. The free proline content was up to 80% lower in 1 mM ACC treated callus grown for 30 days on medium with or without 12 mM proline, respectively, as compared to each control. These studies indicate that ethylene action inhibitors such as norbornadiene and silver nitrate can be used to increase plant regeneration efficiency from maize callus cultures.Abbreviations ACC l-aminocyclopropane-l-carboxylic acid - gfw gram fresh weight     

Promotion ofin vitro shoot formation from excised roots of silktree (Albizzia julibrissin) by an oxime ether derivative and other ethylene inhibitors

Summary This report describes the regeneration response of excised seedling roots of silktree (Albizzia julibrissin) to added ethylene precursors/generators (1-amino-cyclopropane-1-carboxylic acid [ACC], 2-chloroethylphosphonic acid [CEPA]), biosynthesis inhibitors (aminoethoxyvinylglycine [AVG], an oxime ether derivative [OED={[(ispropylidene)-amino]oxy}-acetic acid-2-(methoxy)-2-oxoethyl ester], CoCl² [Co⁺⁺]), and an ethylene action inhibitor (AgNO₃ [Ag⁺]). When placed on B5 medium, about 50% of the control explants formed shoot buds within 15 days. Addition of ACC or CEPA (1–10 µM) to the culture medium decreased both the percentage of cultures forming shoots and the number of shoots formed per culture. In contrast, AVG and OED (1–10 µM) increased shoot formation to almost 100% and increased the number of shoots formed per culture. Likewise, both Co⁺⁺ and Ag⁺ (1–10 µM) increased shoot regeneration, but the number of shoots produced after 30 days was less than with AVG or OED. The inhibitors of ethylene biosynthesis were partially effective in counteracting the inhibitory effect of ACC on shoot formation. These results suggest that modulation of ethylene biosynthesis and/or action can strongly influence the formation of adventitious shoots from excised roots of silktree.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - CEPA 2-chloroethylphosphonic acid - OED oxime ether derivative     

Assay for and enzymatic formation of an ethylene precursor, 1-aminocyclopropane-1-carboxylic acid

A simple and sensitive chemical assay was developed for 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of ethylene. The assay is based on the liberation of ethylene from ACC at pH 11.5 in the presence of pyridoxal phosphate, MnCl₂ and H₂O₂. This assay was used to detect ACC in extracts of tomato fruits (Lycopersicon esculentum Mill.) and to measure the activity of a soluble enzyme from tomato fruit that converted S-adenosylmethionine (SAM) to ACC. The enzyme had a K_m of 13 M for SAM, and conversion of SAM to ACC was competitively and reversibly inhibited by aminoethoxyvinylglycine (AVG), an analog of rhizobitoxine. The K_i value for AVG was 0.2 M. The level of the ACC-forming enzyme activity was positively correlated with the content of ACC and the rate of ethylene formation in wild-type tomatoes of different developmental stages. Mature fruits of the rin (non-ripening) mutant of tomato, which only produce low levels of ethylene, contained much lower levels of ACC and of the ACC-forming enzyme activity than wild-type tomato fruits of comparable age.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG ammoethoxyvinylglycine, the aminoethoxy analog of rhizobitoxine L-2-amino-4-(2-aminoethoxy)-trans-3-butenoic acid - SAM S-adenosyl-L-methionine Michigan Agricultural Experiment Station No. 8876     

Gibberellin-induced ethylene production and its effect on cowpea epicotyl elongation

The effect of gibberellin A₁ (GA₁) on production of ethylene by cowpea (Vigna sinensis cv Blackeye pea no. 5) epicotyl explants and its relationship to epicotyl elongation was investigated. The explants were placed upright in water and incubated in sealed culture tubes or in large jars. GA, and IAA in ethanol solution were injected into the subapical tissues of the decapitated epicotyls. Cowpea epicotyl explants elongated after GA but not after IAA treatment, and they were very sensitive to exogenous ethylene. As little as 0.14 1/1 ethylene reduced significantly GA₁-induced epicotyl elongation.Treatment with GA₁ induced the production of ethylene which began 10 h after GA application, showed a peak at about 22 h and then declined. The yield of ethylene was proportional to the amount of GA, injected. The inhibition of epicotyl elongation in closed tubes was avoided by absorbing ethylene released with Hg(Cl0₄)₂ , or by adding AVG to the incubation solution to inhibit ethylene production. Treatment with IAA elicited a rapid production of ethylene which ceased about 10 h after application. The effects of IAA and GA₁ on ethylene production were additive.Abbreviations AVG aminoethoxyvinylglycine 2-amino-4-(2-aminoethoxy)-trans-3butenoic acid - ACC 1-aminocyclopropane-1-carboxylic acid - GA gibberellin - IAA indole-3-acetic acid     

Enhancement of shoot regeneration from cotyledon explants of Brassica rapa ssp oleifera through pretreatment with auxin and cytokinin and use of ethylene inhibitors

The presence of benzyladenine or naphthaleneacetic acid in seed germination medium markedly enhanced subsequent shoot regeneration from the base of the excised cotyledon explants of Brassica rapa cv. Horizon. Cotyledon explants from younger seedlings (3 or 4-day old) produced more shoots than those from older seedlings. Addition of the ethylene inhibitor aminoethoxyvinylglycine (1.0 M) to the regeneration medium improved shoot regeneration three fold.Abbreviations AVG aminoethoxyvinylglycine - BA benzyladenine - MGBG methylglyoxal-bisguanylhydrazone - MSBN ms (murashige & skoog 1962) medium supplemented with 4.4 m BA & 5.4 m NAA, 2% sucrose - NAA naphthaleneacetic acid     

Interaction of karrikinolide and ethylene in controlling germination of dormant <Emphasis Type="Italic">Avena fatua</Emphasis> L. caryopses

Caryopses of Avena fatua L. are dormant after harvest and germinate poorly at 20 °C. Dormancy was released by after-ripening the dry caryopses in the dark at 25 °C for 3 months. Karrikinolide (butenolide, 3-methyl-2H-furo[2,3-c]pyran-2-one, KAR₁), in contrast to exogenous ethylene and the precursor of ethylene biosynthesis 1-aminocyclopropane-1-carboxylic acid (ACC), completely overcame dormancy. The effect of KAR₁ was not affected by aminoethoxyvinylglycine (AVG), α-aminoisobutyric acid (AIB) and CoCl₂, inhibitors of ACC synthase and oxidase, respectively. 2,5-Norbornadiene (NBD), a reversible inhibitor of ethylene binding to its receptor, counteracted the stimulatory effect of KAR₁. Ethylene, ethephon and ACC counteracted and AVG reinforced inhibition caused by norbornadiene. Inhibition due to norbornadiene, applied during the first 3 days of imbibition in the presence of KAR₁, disappeared after transfer to air or ethylene. The obtained results confirm that KAR₁ breaks dormancy and indicate that ethylene alone plays no role in releasing dormancy of Avena fatua caryopses. KAR₁ probably did not relieve dormancy via the stimulation of ethylene biosynthesis. Some level of endogenous ethylene is probably required for ethylene action, which might be required for releasing dormancy by KAR₁ or for subsequent germination of caryopses after removing dormancy.     

Inhibition of ethylene synthesis in tomato plants subjected to anaerobic root stress

Enhanced ethylene production and leaf epinasty are characteristic responses of tomato (Lycopersicon esculentum Mill.) to waterlogging. It has been proposed (Bradford, Yang 1980 Plant Physiol 65: 322-326) that this results from the synthesis of the immediate precursor of ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), in the waterlogged roots, its export in the transpiration stream to the shoot, and its rapid conversion to ethylene. Inhibitors of the ethylene biosynthetic pathway are available for further testing of this ACC transport hypothesis: aminooxyacetic acid (AOA) or aminoethoxyvinylglycine (AVG) block the synthesis of ACC, whereas CO²⁺ prevents its conversion to ethylene. AOA and AVG, supplied in the nutrient solution, were found to inhibit the synthesis and export of ACC from anaerobic roots, whereas Co²⁺ had no effect, as predicted from their respective sites of action. Transport of the inhibitors to the shoot was demonstrated by their ability to block wound ethylene synthesis in excised petioles. All three inhibitors reduced petiolar ethylene production and epinasty in anaerobically stressed tomato plants. With AOA and AVG, this was due to the prevention of ACC import from the roots as well as inhibition of ACC synthesis in the petioles. With Co²⁺, conversion of both root- and petiole-synthesized ACC to ethylene was blocked. Collectively, these data support the hypothesis that the export of ACC from low O₂ roots to the shoot is an important factor in the ethylene physiology of waterlogged tomato plants.     

Auxin-induced ethylene biosynthesis in subapical stem sections of etiolated seedlings of Pisum sativum L.

1-Aminocyclopropane-1-carboxylic acid (ACC) stimulated the production of ethylene in subapical stem sections of etiolated pea (cv. Alaska) seedlings in the presence and absence of indole-3-acetic acid (IAA). No lag period was evident following application of ACC, and the response was saturated at a concentration of 1 mM ACC. Levels of endogenous ACC paralleled the increase in ethylene production in sections treated with different concentrations of IAA and with selenoethionine or selenomethionine plus IAA. The IAA-induced formation of both ACC and ethylene was blocked by the rhizobitoxine analog aminoethoxyvinylglycine (AVG). Labelling studies with L-[U-¹⁴C]methionine showed an increase in the labelling of ethylene and ACC after treatment with IAA. IAA had no specific effect on the incorporation of label into S-methylmethionine or homoserine. The specific radioactivity of ethylene was similar to the specific radioactivity of carbon atoms 2 and 3 of ACC after treatment with IAA, indicating that all of the ethylene was derived from ACC. The activity of the ACC-forming enzyme was higher in sections incubated with IAA than in sections incubated with water alone. These results support the hypothesis that ACC is the in-vivo precursor of ethylene in etiolated pea tissue and that IAA stimulates ethylene production by increasing the activity of the ACC-forming enzyme.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine, the aminoethoxy analog of rhizobitoxine - IAA indole-3-acetic acid - SAM S-adenosylmethionine - SMM S-methylmethionine     

Role of Ethylene on de Novo Shoot Regeneration from Cotyledonary Explants of Brassica campestris ssp. pekinensis (Lour) Olsson in Vitro

The promotive effect of AgNO₃ and aminoethoxyvinylglycine (AVG) on in vitro shoot regeneration from cotyledons of Brassica campestris ssp. pekinensis in relation to endogenous 1-amino-cyclopropane-1-carboxylic acid (ACC) synthase, ACC, and ethylene production was investigated. AgNO₃ enhanced ACC synthase activity and ACC accumulation, which reached a maximum after 3 to 7 days of culture. ACC accumulation was concomitant with increased emanation of ethylene which peaked after 14 days. In contrast, AVG was inhibitory to endogenous ACC synthase activity and reduced ACC and ethylene production. The promotive effect of AVG on shoot regeneration was reversed by 2-chloroethylphosphonic acid at 50 micromolar or higher concentrations, whereas explants grown on AgNO₃ medium were less affected by 2-chloroethylphosphonic acid. The distinctive effect of AgNO₃ and AVG on endogenous ACC synthase, ACC, and ethylene production and its possible mechanisms are discussed.     

Ethylene release from green spruce needles involves a combination of ACC-dependent and independent pathways

Aminoethoxyvinylglycine (AVG) and cobalt ions strongly inhibit the conversion of added methionine or aminocyclopropane-1-carboxylic acid (ACC) into ethylene by green-coloured, non-stressed Norway spruce (Picea abies L.) needles but only 30%–40% of basal ethylene formation is affected by such inhibitors. In addition, free radical-mediated ACC-independent ethylene formation (AIEF) of the type released by brown-coloured spruce needles also occurs in extracts from healthy green-coloured needles. Treatment with CdCl₂ (10 mM), Na₂S₂O₅ (5 mM) or FeSO₄ (10 mM) induces 3–7 fold increases in the rates of ethylene evolution from green-coloured needles. However, only Cd²⁺-induced ethylene formation is inhibited by AVG while ethylene induced by S₂O₅ ^2- or Fe²⁺ is insensitive to added AVG although increased levels of ACC have also been detected in these treatments. Nevertheless, ethylene-forming decomposition of the precursors of AIEF is accelerated by S₂O₅ ^- or Fe²⁺ which indicates that the ethylene released from green-coloured spruce needles is formed by a combination of both the ACC-dependent and AIEF pathways.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - AIEF ACC-independent ethylene formation - EFE ethylene-forming enzyme - MACC N-malonyl(amino)cyclopropane-1-carboxylic acid - DTBN di-tert-butylnitroxide - MNP 2-methyl-2-nitrosopropane - SAM S-adenosylmethionine - TEMPO 2,2,6,6-tetramethyl-1-piperidine-N-oxyl     

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.     

Involvement of ethylene on growth and plant regeneration in callus cultures of Heliconia psittacorum L.f.

The level of ethylene accumulated in morphogenic callus cultures of Heliconia psittacorum L.f. was only one quarter that of non-morphogenic cultures. The rate of ethylene production in the morphogenic callus cultures during early stages of differentiation of protocorm-like bodies leading to plantlet regeneration was 10-fold higher than that during callus proliferation. In cultures sealed with gastight serum caps, fresh weight gain was reduced 2-to 3-fold compared to those that were closed with Kaputs. Treatment with 1-aminocyclopropane-1-carboxylic acid ( 100 M) caused complete inhibition of plant regeneration from the morphogenic callus on subsequent culture under inductive conditions. Silver nitrate and aminoethoxyvinylglycine also reduced plant regeneration. These results indicate that while high levels of ethylene were inhibitory, a low level of endogenous ethylene production may be necessary during the plant regeneration phase in callus cultures of Heliconia.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - AC activated charcoal - ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethoxyvinylglycine - BM basal medium - CH casein hydrolysate - DM development medium - MM maintenance medium - PLB protocorm-like body     

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     

Effect of Nitrate and Aminoethoxyvinylglycine on Cicer Arietinum L. Nodules

The chickpea (Cicer arietinum L.) cv. HC-1 was raised in earthen pots filled with dune sand in screenhouse. At vegetative stage, i.e. 40 – 45 d after sowing, 10, 20 and 40 mM NO₃ ^– was applied through rooting medium. After 24 h of NO₃ ^– treatments an ethylene biosynthesis inhibitor, aminoethoxyvinylglycine (AVG) in concentration 5 M was given. A conspicuous increase in (5 – 9 fold) ethylene evolution in nodules was noticed after NO₃ ^– treatments. This rise was parallel to the increase in 1-aminocyclopropane-1-carboxylic acid (ACC) content and ACC oxidase activity. On the contrary, a sharp decline in ACC content, ACC oxidase activity and ethylene evolution was observed when AVG was given. A decrease of in acetylene reduction assay (ARA) with NO₃ ^– treatments was associated with decline in cytosolic pH (from 6.12 to 5.45), leghemoglobin (Lb) content, accumulation of H₂O₂ and with the loss of membrane integrity. The lipid peroxidation, followed as MDA production and electrolyte leakage increased with NO₃ ^– treatments, however, the level of MDA was brought down in AVG-treated nodules. Results confirm that ethylene might be involved in mechanism by which the functioning of nodules is adversely affected by NO₃ ^–.