Ca2+ effects on ethylene, carbon dioxide and 1-aminocyclopropane-1-carboxylic acid synthase activity

The response of pericarp disks from ripening tomato (Lycopersicon esculentum Mill. cv. Traveler‘76) to CaCl₂, additions was studied to determine the effect of Ca²⁺ on ethylene and CO₂ production. Application of 5 mM CaCl₂ resulted in a 2, 20, 33, 39, and 50% increase in ethylene production in disks obtained from preclimacteric minimum, climacteric rise, climacteric peak, one, and two days postclimacteric fruit, respectively. CaCl₂ concentrations of 10 and 50 mM gave no additional stimulation of ethylene production; CO₂ production at 5 mM CaCl₂ was not different from controls, but is increased at 10 and 50mM CaCl₂. CaCl₂ also increased ethylene production in disks treated with 1-aminocyclopropane-1-carboxylic acid (ACC) or aminoethoxy-vinylglycine. Chloride salts of K⁺, Na⁺, Mg²⁺, Sr²⁺ and La³⁺ did not stimulate ethylene production. SrCl₂ stimulated ethylene production to a lesser degree than CaCl₂. Disks from potato (Solanum tuberosum L. cv. Katahdin) tubers produced greater quantities of ethylene and ACC when 5 mM CaCl₂ was included in the incubation medium (K. B. Evensen, 1983. Physiol. Plant. 60:125–128). Ca²⁺-treated disks had more than three times as much ACC synthase activity as control disks after 18 to 24 h incubation, when ethylene and ACC were maximal. The apparent K_m for S-adenosylmethionine was 13 μM at 29°C, pH 8.0 in extracts from both Ca²⁺-treated and control disks. Inclusion of 1 to 50 mM CaCl₂ in the assay medium did not significantly affect enzyme activity. ACC synthase extracted from control and Ca²⁺-treated disks had a pH optimum of 8.5 and an apparent molecular weight of 72 kdalton, estimated by gel filtration. It is likely that the presence of Ca²⁺ in the buffer allows greater synthesis of ACC synthase as part of the wound-healing response in potato, while in tomato the predominant effect is on membrane stabilization.     

Synergistic enhancement of ethylene production and germination with kinetin and 1-aminocyclopropane-1-carboxylic Acid in lettuce seeds exposed to salinity stress

Relief of salt (0.1 molar NaCl) stress on germination of lettuce (Lactuca sativa L., cv Mesa 659) seeds occurred with applications of 0.05 millimolar kinetin (KIN) and 1 to 10 millimolar 1-aminocyclopropane 1-carboxylic acid (ACC). Treatment with KIN enhanced the pregermination ethylene production under saline condition. A synergistic or an additive enhancement of pregermination ethylene production and germination occurred under saline condition in the presence of KIN and a saturating dose (10 millimolar) of ACC. No KIN-ACC synergism was noted in ethylene production or germination under nonsaline condition. Addition of 1 millimolar aminoethoxyvinylglycine (AVG) inhibited the KIN-enhanced pregermination ethylene production (85 to 89%) and germination (58%) under saline condition but not the synergistic effect of KIN + ACC on ethylene production. Under nonsaline condition, AVG had no effect on germination even though ethylene production was strongly inhibited. Alleviation of salt stress by KIN was inhibited in a competitive manner by 2,5-norbornadiene (NBD) (0.02-0.2 milliliter per liter), and the addition of ACC and/or ethylene reduced this inhibition. An increase in the pregermination ethylene production and germination occurred also by cotylenin E (CN) under saline condition. However, neither AVG (1 millimolar) nor NBD (0.02 to 0.2 milliliter per liter) prevented the relief of salt stress by CN. Thus, KIN may alleviate salt stress on germination by promoting both ACC production and its conversion to ethylene. Rapid utilization of ACC may be the basis for the synergistic or the additive effect of KIN plus ACC. The need for ethylene production and action for the relief of salt stress is circumvented by a treatment with CN.     

Evidence that brassinosteroid stimulates auxin-induced ethylene synthesis in mung bean hypocotyls between S-adenosylmethionine and 1-aminocyclopropane-1-carboxylic acid

Brassinosteroid (BR) stimulation of auxin-induced ethylene production and the particular step at which BR acts to promote such synthesis were studied in mung bean ( Vigna radiata L. Rwilcz cv. Berken) hypocotyl segments. Increasing concentrations of methionine alone and in combination with 3 μ M BR and 10 μ M IAA had a minimal effect on ethylene production. With increasing concentrations of 1-aminocyclopro-pane-1-carboxylic acid (ACC), however, ethylene production increased. BR or IAA further enhanced ethylene production with maximum rates occurring when these compounds were added together with ACC. The addition of 10 μ M CoCl₂ in conjunction with BR and/or IAA resulted in 85–97% inhibition of ethylene production. When 20 μ M cycloheximide was used in conjunction with BR and/or IAA there was a complete inhibition of ethylene production. Total inhibition also resulted when 1.0 μ M aminoethoxy-vinylglycine (AVG) was used in combination with BR and/or IAA. AVG alone had no effect on ACC conversion to ethylene.     

Autoinhibition of Ethylene Production in Citrus Peel Discs : SUPPRESSION OF 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID SYNTHESIS

Wound ethylene formation induced in flavede tissue of citrus fruit (Citrus paradisi MacFad. cv. Ruby Red) by slicing was almost completely inhibited by exogenous ethylene. The inhibition lasted for at least 6 hours after removal of exogenous ethylene and was then gradually relieved. The extent of inhibition was dependent upon the concentration of ethylene (1 to 10 microliters/liter) and the duration of treatment. The increase in wound ethylene production in control discs was paralleled by an increase in 1-aminocyclopropane-1-carboxylic acid (AAC) content, whereas in ethylene-treated discs there was little increase in ACC content. Application of ACC completely restored ethylene production in ethylene-pretreated discs, indicating that the conversion of ACC to ethylene is not impaired by the presence of ethylene. Thus, autoinhibition of ethylene synthesis was exerted by reducing the availability of ACC. Ethylene treatment resulted in a decrease in extractable ACC synthase activity, but this decrease was too small to account for the marked inhibition of ACC formation. The data indicate that autoinhibition of ethylene production in citrus flavede discs results from suppression of ACC formation through repression of the synthesis of ACC synthase and inhibition of its activity.     

Calcium regulation of exogenous and endogenous 1-aminocylopropane-1-carboxylic acid bioconversion to ethylene

Ethylene production and overall levels of free and conjugated 1-aminocyclopropane-1-carboxylic acid (ACC) were studied in parenchymatous tissues, excised from clmacteric apples ( Malus domestica Borkh. cv. Granny Smith) and infiltrated with an incubation medium containing 0, 1, 10 or 100 m M Ca²⁺, with or without exogenous ACC (2 m M ). Irrespective of whether exogenous ACC was applied or not, ethylene production was inhibited to the same extent (40%) by an apoplastic effect of 100 m M Ca²⁺. In the absence of external ACC, the inhibition was associated with an increase in total endogenous ACC and may be related to a reduction in the rate of the last step of ethylene pathway. This suggests that the ethylene-forming enzyme (EFE) is localized in the plasma membrane. Low Ca²⁺ concentrations (1 m M ) enhanced basal ethylene synthesis due to influx of Ca²⁺ into the cytosol, while overall concentrations of ACC in the tissue decreased. However, 1 m M Ca²⁺ did not stimulate ACC-dependent ethylene formation. Thus, Ca²⁺ influx may stimulate the translocation of endogenous ACC from synthesis or storage compartment (s) to reactive site(s) of the plasma membrane. The concentration of 10 m M Ca²⁺ had no effect on basal ethylene production and appears to represent a balance point between the stimulating and inhibiting effects of 1 and 100 m M Ca²⁺, respectively, Furthermore, the charge-times of exogenous ACC observed with 0, 1 and 10 m M Ca²⁺ suggest that EFE is located on the inner side of the plasma membrane.     

1-Aminocyclopropane-1-carboxylic acid as a substrate of peroxidase: conditions for oxygen consumption, hydroperoxide generation and ethylene production

Conditions in which 1-aminocyclopropane-1-carboxylic acid (ACC) functions as a substrate of peroxidase have been investigated by measuring oxygen consumption in the reaction medium and the production of ethylene. In both cases, the presence of Mn2+ and either H2O2 or the activated form of peroxidase, namely compound I of peroxidase, was found to be essential. Both oxygen consumption and ethylene production were dependent on enzyme concentration, the optimum ACC/Mn2+ ratio being 1:1. Oxygen consumption in a system with ACC, Mn2+ and compound I showed an enzyme-dependent lag phase and then proceeded to total depletion, suggesting that the system itself generates hydroperoxides that completed the catalytic cycle of the enzyme. The presence of these hydroperoxides in the reaction medium was detected by a colorimetric method. High H2O2 concentration progressively decreased oxygen consumption, the same effect being produced by catalase. Ethylene production was oxygen dependent, mediated by ACC-free radicals and gave a poor yield. The results suggest that the fate of these ACC-free radicals determines the yield in ethylene. These radicals must be oxidized immediately, otherwise their stabilization to hydroperoxides would prevent ethylene production.     

Biosynthesis of Auxin-Induced Ethylene. Effects of Indole-3-Acetic Acid, Benzyladenine and Abscisic Acid on Endogenous Levels of 1-Aminocyclopropane-l-Carboxylic Acid (ACC) and ACC Synthase

Auxin-induced ethylene biosynthesis and its regulatory stepsin etiolated mung bean hypocotyl segments were examined. Theendogenous content of 1-aminocyclopropane- 1-carboxylic acid(ACC), an immediate precursor of ethylene, increased correspondingto the rate of ethylene production. Benzyladenine (BA), whichis a synergistic stimulator of auxin-induced ethylene production,increased the ACC content parallel to the rate of ethylene productionin the presence of IAA, but failed to increase the ACC contentin the absence of IAA while ethylene production was significantlystimulated by BA. Abscisic acid (ABA) inhibited the formationof ACC. The ACC synthase activity in the tissue was increasedby IAA, and the increase was further promoted by the presenceof BA. Cycloheximide severely inhibited the development of auxin-inducedACC synthase. The enzymatic properties of mung bean ACC synthasewere similar to those of the tomato fruit enzyme. Aminoethoxyvinylglycine(AVG) and aminooxyacetic acid, which inhibit the ACC synthasereaction, stimulated the development of ACC synthase. The regulatorymechanisms of the growth regulators are discussed in relationto ACC formation. (Received December 3, 1980; Accepted January 22, 1981)     

Stimulation of somatic embryogenesis in carrot by ethylene: Effects of modulators of ethylene biosynthesis and action

Endogenous levels of ethylene appeared to he suhoptimal for somatic embryogenesis in a suspension culture of carrot. Low concentrations of 1-aminocyclopropane-1-carboxylic acid (ACC). 2-chloroethylphosphonic acid (ethephon) and elhylene stimulated embryogenesis whereas higher concentrations were inhibitory. The stimulation by ACC was through its conversion to ethylene. whereas the inhibition by ACC was not. Low concentrations of AgNO₃. an inhibitor of ethylene action, inhibited embryo-genesis but stimulated ethylene production. Aminoethoxyvinylglycine (AVG) and aminooxyacetic acid (AOA). commonly used inhibitors of ACC synthase. inhibited both embryogenesis and ethylene production. However, the inhibition of embryogenesis was not related to the inhibition ote ethylene production. Very low concentrations of AVG stimulated embryo production in a way unrelated to its effect on ethylene production. Salicylic acid and CoCl₂. inhibitors of ACC oxidase in other systems, inhibited embryogenesis but. again, in way(s) unrelated to their inhibition of ethylene production. In fact, low concentrations of salicylic acid stimulated rather than inhibited ethylene production. The results show that in suspension-cultured cells, caution is warranted in the interpretation of results obtained with agents presumed to inhibit ethylene biosynthesis. The stimulation of somatic embryogenesis by ethylene unequivocally shows that the inhibition of embryo development by 2.4-dichlorophenoxyacetic acid (2.4-D) and other auxins cannot be through their stimulatory effect on ethylene production.     

Ethylene synthesis and growth in embryogenic tissue of Norway spruce: Effects of oxygen, 1-aminocyclopropane-1-carboxylic acid, benzyladenine and 2,4-dichlorophenoxyacetic acid

Ethylene production from an embryogenic culture of Norway spruce ( Picea abies L.) was generally low. ca 2.5 nl g⁻¹ h⁻¹, whereas 1-aminocyclopropane-1 -carboxylic acid (ACC) concentration was high, fluctuating between 50 and 500 nmol g⁻¹ during the 11-day incubation period. Hypoxia (2.5 and 5 kPa O₂) rapidly inhibited ethylene production without subsequent accumulation of ACC. Exogenous ACC (1, 10 and 100 μ M ) did not increase ethylene production, but the highest concentrations inhibited tissue growth. Ethylene (7 μl I⁻¹) did not inhibit growth either when supplied as ethephon in the medium or in a continuous flow system. Benzyladenine (BA) had little effect on ethylene production, although it was necessary for sustaining the ACC level. Omission of 2.4-dichloro-phenoxyacetic acid (2.4-D) from the medium caused ethylene production to increase from about 2.5 to 7 nl g⁻¹ h⁻¹ within the 11-day incubation period. Although 2.4-D did not specifically alter the endogenous level of ACC, the lowest ACC level, 33 nmol g⁻¹, was observed in tissue treated with 2.4-D (22.5 μ M ) and no BA for 11 days. Data from this treatment were used to estimate the kinetic constants for ACC oxidase, the apparent K_m was 50 μ M and V_max 2.7 nl g⁻¹ h⁻¹. Growth of the tissue was strongly inhibited by 2.4-D in the absence of BA, but weakly in the presence of BA (4.4 μ M ). The results suggest that ethylene or ACC may be involved in the induction of embryogenic tissue and in the early stages of embryo maturation.     

Factors increasing ethylene production enhance the sensitivity of root growth to auxins

Light inhibits root elongation, increases ethylene production and enhances the inhibitory action of auxins on root elongation of pea ( Pisum sativum L. cv. Weibulls Marma) seedlings. To investigate the role of ethylene in the interaction between light and auxin, the level of ethylene production in darkness was increased to the level produced in light by supplying 1-aminocyclopropane-1-carboxylic acid (ACC) or benzylaminopurine (BAP). Ethylene production was measured in excised root tips after treatment of intact seedlings for 24 h, while root growth was measured after 48 h. Auxin, at a concentration causing a partial inhibition of root elongation, did not increase ethylene production significantly. A 4-fold increase in ethylene production, caused either by light, 0.1 μ M ACC or 0.1 μ M BAP, inhibited root elongation by 40–50%. The auxins 2,4-dichlorophenoxyacetic acid and indolebutyric acid applied at 0.1 μ M inhibited root elongation by 15–25% in darkness but by 50–60% in light. Supply of ACC or BAP in darkness enhanced the inhibitory effects of auxins to about the same extent as in light. The inhibition caused by the auxins as well as by the BAP was associated with swelling of the root tips. ACC and BAP treatment synergistically increased the swelling caused by auxins. We conclude that auxin and ethylene, when applied or produced in partially inhibitory concentrations, act synergistically to inhibit root elongation and increase root diameter. The effect of light on the response of the roots to auxins is mediated by a light-induced increase in ethylene production.     

Changes in Ethylene Production and 1-Aminocyclopropane-l-carboxylic acid Levels in Climacteric Apple Fruits Ralls under Low O2 and High CO2

Ethylene production was severely inhibited in climacteric applefruits treated with either low O2(O2 :1–3%, CO2: 0%)or high CO2(O2:15–21%, CO2:10–20%) for 4, 10, and 15 days, respectively. In treatment with low O2 for 10 or 15days, 1-aminocyclopropane-1-carboxylic acid (ACC) was accumulated in large quantity,but in the fruit treated with high CO2, the content of ACC was slightly lower than thatin control fruit. When the fruit was turned to air after 4-days treatment with low O2, ethylene production and ACC content were able to recover to control level. But in the fruits withlow O2 for 10 or 15 days ethylene production was 100 times lower, and ACC contentwas much higher than those in control even 30-35 days after they were turned to air. It appears that inhibitory effect of the low O2 treatment for longer than 10 days on theconversion of ACC to ethylene was irreversible. In the case of high CO2 treatment fordifferent periods ethylene production obviously decreased at first, then followed by arapid increase. When the fruits were turned to air ethylene production in the treat-ment for 4 days was able to recover to control level, but it remained much lower in tre-atment for 10 or 15 days than that in control throughout the period of recovery. However, ACC contents in both treatments were slightly lower than those in control during a few days after the removal of treatment, but increased slightly after 2-3 weeks.Furthemore, the ability of flesh discs to convert exogenous ACC to ethylene was redu-ced remarkably by the treatment of fruits with either low O2 or high CO2 for longerthan 10 days.     

Fusicoccin, an inhibitor of brassinosteroid-induced ethylene production

Fusicoccin was evaluated for its effects on brassinosteroid (BR), indole-3-acetic acid (IAA) and BR + IAA-induced ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC) and ACC-synthase production by etiolated mung bean ( Vigna radiata L. Rwilez cv. Berken) hypocotyl segments. Fusicoccin inhibition of ethylene and ACC production induced by 2 μ M BR started at concentrations as low as 0.05 μ M . Maximum inhibition occurred at a 1 μ M concentration with no further inhibition at higher concentrations tested. Fusicoccin (1 μ M ) was effective in the inhibition of BR-induced ethylene, ACC and ACC-synthase production at low and high concentrations of BR.
Fusicoccin at concentrations as high as 2 μ M had no effect on ethylene and ACC production promoted by low concentrations of IAA (1 to 10 μ M ). When higher concentrations (100–1000 μ M ) of IAA were used, fusicoccin (1 μ M ) had an inhibitory effect on ethylene and ACC production. Interestingly, fusicoccin (1 μ M ) had little or no effect on ACC-synthase promoted by high concentrations of IAA (1000 μ M ).
When BR and IAA were used in combination, fusicoccin inhibited ethylene and ACC production at concentrations as low as 0.05 μ M with maximum inhibition occurring at 0.5 μ M . At a 1 μ M concentration, fusicoccin was effective in inhibiting the synergistic stimulation of ACC-synthase promoted by BR and IAA.     

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

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

钙对香蕉采后乙烯释放的抑制

本实验用CaCl_2溶液对香蕉(Musa acuminata cf. 'Dwarf Davendish')组织进行真空浸透处理,研究Ca~(2 )对香蕉采后乙烯释放、EFE活性、ACC水平以及ACC/MACC比值的影响。结果表明,Ca~(2 )处理可抑制香蕉果皮和果肉组织乙烯生成,对抑制果皮的乙烯生成尤为明显。Ca~(2 )处理还可降低内源ACC水平,抑制EFE活性。结果还显示,Ca~(2 )处理对组织中ACC/MACC比值有一定影响。     

Bicarbonate/CO(2)-Facilitated Conversion of 1-Amino-cyclopropane-1-carboxylic Acid to Ethylene in Model Systems and Intact Tissues

Bicarbonate markedly enhances ethylene production from 1-aminocyclopropane-1-carboxylic acid (ACC) in model chemical systems where the conversion is free radical-mediated, in thylakoid membrane suspensions of Phaseolus vulgaris L. cv Kinghorn where the reaction is light-dependent, and in microsomal membrane suspensions and intact tissues where the reaction is enzymically mediated. In two model systems generating free radicals—the Fenton reaction and a reaction mixture containing xanthine/xanthine oxidase, NaHCO₃ (200 millimolar) increased the formation of ethylene from ACC by 84-fold and 54-fold, respectively. Isolated thylakoid membranes also proved capable of ACC-dependent ethylene production, but only upon illumination, and this too was enhanced by added NaHCO₃. As well, light-induced inhibition of ACC-dependent ethylene production by leaf discs was relieved by adding 200 millimolar NaHCO₃. Finally, NaHCO₃ (200 millimolar) augmented ACC-dependent ethylene production from young carnation flowers by about 4-fold, and the conversions of ACC to ethylene by microsomes isolated from carnation flowers and etiolated pea epicotyls were higher by 1900 and 62%, respectively, in the presence of 200 millimolar NaHCO₃.

This increased production of ethylene appears not to be due to bicarbonate or CO₂-induced release of the gas from putative receptor sites, since the addition of NaHCO₃ to sealed reaction mixtures after the ACC to ethylene conversion had been terminated had no effect. Spin-trapping studies have confirmed that bicarbonate does not facilitate the formation of free radicals thought to be involved in the conversion of ACC to ethylene. Nor did bicarbonate alter the physical properties of the membrane bilayer, which might indirectly modulate the activity of the membrane-associated enzyme capable of converting ACC to ethylene. Rather, bicarbonate appears to directly facilitate the conversion of ACC to ethylene, and the data are consistent with the view that CO₂ derived from bicarbonate is the active molecular species.

     

Ethylene formation in plant mitochondria. Dependence on the transport of 1-aminocyclopropane-1-carboxylic acid across the membrane

The mitochondrial fraction isolated from plumular hooks of etiolated pea seedlings ( Pisum sativum L. cv. Kelvedon Wonder) displayed a ten-fold higher rate of ethylene formation from 1-aminocyclopropane-1-carboxylic acid [ACC; 3.2 nmol C₂H₄ (mg protein ⁻¹)h⁻¹], than the tissue from which it was isolated. When the ionophores valinomycin or nigericin were added, a 60- to 70-fold increase in activity in intact mitochondria over the activity in plumular hooks was obtained for ethylene formation under the same conditions, and a 20-fold increase was obtained upon addition of gramicidin. The addition of ionophores did not affect the rate of ethylene formation in submitochondrial particles (55% inside-out as determined by cytochrome oxidase latency) which already exhibited a 2–3-fold higher specific activity than intact mitochondria. Low concentrations of the detergents cholate and deoxycholate increased mitochondrial ethylene formation activity and had no effect on the rate of the reaction in submitochondrial particles. These results support the suggestion that ACC conversion to ethylene is associated with the inner side of the inner mitochondrial membrane and that transport across the intact mitochondrial membrane is rate-limiting in the reaction.     

De novo shoot morphogenesis and plant growth of mustard (Brassica juncea) in vitro in relation to ethylene

Role of ethylene in de novo shoot morphogenesis from explants and plant growth of mustard ( Brassica juncea cv. India Mustard) in vitro was investigated, by culturing explants or plants in the presence of the ethylene inhibitors aminoethoxyvinylglycine (AVG) and AgNO₃. The presence of 20 μ M AgNO₃ or 5 μ M AVG in culture medium containing 5 μ M naphthaleneacetic acid and 10 μ M benzyladenine were equally effective in promoting shoot regeneration from leaf disc and petiole explants. However, AgNO₃ greatly enhanced ethylene production which reached a maximum after 14 days, whereas ethylene levels in the presence of AVG remained low during 3 weeks of culture. The promotive effect of AVG on shoot regeneration was overcome by exogenous application of 25 μ M 2-chloroethylphosphonic acid (CEPA), but AgNO_3-induced regeneration was less affected by CEPA. For whole plant culture, AVG did not affect plant growth, although it decreased ethylene production by 80% and both endogenous levels of 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC by 70–80%. In contrast, AgNO₃ stimulated all 3 parameters of ethylene synthesis. Both AgNO₃ and CEPA were inhibitory to plant growth, with more severe inhibition occuring in AgNO₃. Leaf discs derived from plants grown with AVG or AgNO₃ were highly regenerative on shoot regeneration medium without ethylene inhibitor, but the presence of AgNO₃ in the medium was inhibitory to regeneration of those derived from plants grown with AgNO₃.     

The site of 1-aminocyclopropane-1-carboxylic acid synthesis in senescing carnation petals

To study the cause of the uneven production of ethylene by upper and basal portions of detached petals of carnation ( Dianthus caryophyllus L. cv. White Sim), the petals were divided and exposed to ethylene (30 μl 1^-1 for 16 h). The treatment induced rapid wilting and autocatalytic ethylene production in the basal portion similar to that induced in entire petals. In contrast to the response in entire petals and the basal portions, the upper portions responded to ethylene by delayed wilting and much lower ethylene production. Aminocyclopropane carboxylic acid (ACC)-synthase activity in the basal portion of the petals was 38 to 400 times that in the upper portion. In untreated detached petal pieces from senescing carnation flowers, ethylene production by the upper portion declined after 6 h while the basal portion was still producing ethylene at a steady rate 18 h later. Application of ACC to the upper portion of senescing petals increased their ethylene production. α-Aminooxyacetic acid (0.5 m M ), reduced the ethylene production of the senescing basal portion more than that of the upper portion. Endogenous ACC content in basal portions of senescing carnation petals was 3 to 4 times higher than in the upper parts. When detached senescing petals were divided immediately after detaching, the endogenous ACC levels in upper portions remained steady or declined during 24 h after division, while in the basal portions the ACC level rose steadily as in the intact petals. There was no change in the conjugated ACC in either portion after 24 h. Benzyladenine (BA) applied as a pretreatment to entire preclimacteric petals greatly reduced the development of ACC-synthase activity of the basal portion, but had little effect on the activity in the upper portion of the petal. In both portions, however, BA effectively reduced the conversion of ACC to ethylene.