Growth and tissue senescence inPrunus avium shoots grownin vitro at different CO3/O2 ratios

Summary The rate of metabolism and biosynthetic processes makein vitro cultures very sensitive to environmental changes, and therefore subject to physiological and morphological alterations leading to senescence in the short term. The effect of three different calibrated atmospheric compositions were studied duringin vitro culture ofPrunus avium shoots. At 0.034% CO₂-21% O₂ (vol/vol), which stimulate the natural atmosphere, the highest growth rate and chlorophyll content were recorded. When grown at 0.09% CO₂-8% O₂ (vol/vol), a favorable condition for photosynthesis and growth, cultures showed a higher percentage of dry matter and elevated ethylene production, but total chlorophyll was lower. These shoots were also highly lignified and fibrous with red pigmentation along the leaves and stems. At 0% CO₂-21% O₂ (vol/vol), in contrast, growth and ethylene formation were inhibited; chlorophyll content was lowest in comparison with the other two environmental conditions, but regreening of tissues was observed after the first half of the culture period. Senescence symptoms, as indicated by decreased chlorophyll, appeared after about 18 d of culture for tissues grown in CO₂-containing atmospheres. These experiments provided evidence that in CO₂-enriched cultures biomass production steadily increased even when chlorophyll decreased. A possible role of CO₂ in promoting tissue-senescence through activation of photooxidative events and ethylene synthesis is discussed.     

Non-symbictic nitrogen fixation in the rhizosphere of Digitaria smutzii stent

Summary The acetylene reduction technique was used to test for the activity of nitrogenase in the rhizosphere of Digitaria smutzii grown in a solodic soil, and in the same soil in the absence of grass. The tests were made in McCartney bottles and regression analysis was used to compare rates of ethylene production. Roots with rhizosphere soil attached, exposed to acetylene and incubated anaerobically for 34 hours produced ethylene at a mean rate of 29 n moles C₂H₄/g root/h. No significant activity was detected under anaerobic conditions in the unplanted soil. Under aerobic conditions, significant but very low rates of ethylene production were observed in both the presence and absence of grass. Temperature treatments within the range 20°–32°C had no significant effect on rates of ethylene production.     

Ethylene: potential key for biochar amendment impacts

Significant increases in root density, crop growth and productivity have been observed following soil additions of biochar, which is a solid product from the pyrolysis of biomass. In addition, alterations in the soil microbial dynamics have been observed following biochar amendments, with decreased carbon dioxide (CO₂) respiration, suppression of methane (CH₄) oxidation and reduction of nitrous oxide (N₂O) production. However, there has not been a full elucidation of the mechanisms behind these effects. Here we show data on ethylene production that was observed from biochar and biochar-amended soil. Ethylene is an important plant hormone as well as an inhibitor for soil microbial processes. Our current hypothesis is that the ethylene is biochar derived, with a majority of biochars exhibiting ethylene production even without soil or microbial inoculums. There was increased ethylene production from non-sterile compared to sterile soil (215%), indicating a role of soil microbes in the observed ethylene production. Production varied with different biomass sources and production conditions. These observations provide a tantalizing insight into a potential mechanism behind the biochar effects observed, particularly in light of the important role ethylene plays in plant and microbial processes.     

Ethylene and ethane production in response to salinity stress

Abstract Ethylene and ethane production in mung bean hypocotyl sections were evaluated as possible indicators of stress due to contact with four salts that are common in natural sites. Ethylene production decreased with increasing concentrations of applied NaCl and KCl. When CaCl₂ was applied, the ethylene evolution was greater. However, when MgCl₂ was applied, ethylene evolution remained high then decreased and at higher salt concentrations again showed an increase. NaCl (up to 0.1 kmol m^?1) and KCl (up to 0.5 kmol m^?3) caused a concentration-dependent increase in ethane production. The ethane production with CaCl₂ was the lowest among the salts tested and only a minute increase was noticed with the increase of concentration from 0.01 to 1 kmol m^?3. Ethane production showed a distinct maximum at 0.2 kmol m^?3 MgCl₂. The introduction of 0.01 kmol m^?3 CaCl₂, as well as anaerobic conditions obtained by purging vials with N₂, eliminated that high ethane production. Respiratory activity of the mung bean hypocotyl sections in MgCl₂ concentrations from 0 to 0.5 kmol m^?3 was correlated with ethane but not with ethylene production. The ethane/ethylene ratio showed three patterns for the four salts tested.     

Requirement for Ethylene Synthesis and Action during Relief of Thermoinhibition of Lettuce Seed Germination by Combinations of Gibberellic Acid, Kinetin, and Carbon Dioxide

Application of exogenous ethylene in combination with gibberellic acid (GA₃), kinetin (KIN), and/or CO₂ has been reported to induce germination of lettuce seeds at supraoptimal temperatures. However, it is not clear whether endogenous ethylene also plays a mediatory role when germination under these conditions is induced by treatment regimes that do not include ethylene. Therefore, possible involvement of endogenous ethylene during the relief of thermoinhibition of lettuce (Lactuca sativa L. cv Grand Rapids) seed germination at 32°C was investigated. Combinations of GA₃ (0.5 millimolar), KIN (0.05 millimolar), and CO₂ (10%) were used to induce germination. Little germination occurred in controls or upon treatment with ethylene, KIN, or CO₂. Neither KIN nor CO₂ affected the rate of ethylene production by seeds. Both germination and ethylene production were slightly promoted by GA₃. Treatments with GA₃+CO₂, GA₃+KIN, or GA₃+CO₂+KIN resulted in approximately 10-to 40-fold increases in ethylene production and 50 to 100% promotion of germination as compared to controls. Initial ethylene evolution from the treated seeds was greater than from the controls and a major surge in ethylene evolution occurred at the time of visible germination. Application of 1 millimolar 2-aminoethoxyvinyl glycine (AVG), an inhibitor of ethylene synthesis, in combination with any of above three treatments inhibited the ethylene production to below control levels. This was accompanied by a marked decline in germination percentage. Germination was also inhibited by 2,5-norbornadiene (0.25-2 milliliters per liter), a competitive inhibitor of ethylene action. Application of exogenous ethylene (1-100 microliters per liter) overcame the inhibitory effects of AVG and 2,5-norbornadiene on germination. The results demonstrate that endogenous ethylene synthesis and action are essential for the alleviation of thermoinhibition of lettuce seeds by combinations of GA₃, KIN, and CO₂. It also appears that these treatment combinations do not act exclusively via promotion of ethylene evolution as the application of exogenous ethylene alone did not promote germination.     

Ethephon application induces symptoms of fruit tissue degeneration in watermelon

Vegetable Research Division, NHRI, 475 Imok-dong, Jangan-gu, Suwon, Gyeonggi-do, 440-706, Republic of Korea Flesh tissue degeneration (called blood-black heart; BBH) of watermelon (Citrullus vulgaris S.) is occasionally observed in Korea. Fruits with BBH have lower quality, a dark-red flesh, and reduced firmness of the rind, often producing an unpleasant flavor. Although causal factors are thought to be undesirable soil moisture conditions, e.g., drought or water-logging, temperature extremes, or virus infection, the mechanism for this physiological disorder is not clearly understood. It is possible that ethylene gas (C₂H₄) is involved in degrading the cell walls. To determine such an implication for ethylene in the occurrence of BBH, we foliar-applied various concentrations of ethephon (100, 200, 400, 800, or 1000 mg L^-1) to watermelon plants at 5 or 10 d prior to harvesting, then monitored the development of this disorder in their fruits. At 400 mg L^-1 or higher, quality was diminished and the fruit had softer rind tissues. About 25% of the fruits harvested at that level exhibited BBH versus 100% of the fruits exposed to 800 or 1000 mg L^-1 ethephon. Concomitant with the onset of BBH, those affected fruits produced elevated amounts of ethylene gas during the 4-d measurement period. Therefore, a high incidence of BBH may well be related to this increased ethylene production, which can be triggered by both unfavorable environmental conditions and inappropriate cultural practices.     

Importance of Time Constants in an Open Flow System: Mathematical Correction of Fast Ethylene Kinetics in Physiological Studies

A mathematical analysis for fast changes of ethylene concentration in an open flow system (non-steady-state conditions) is presented and experimentally tested. In this way it becomes possible to determine true values of ethylene production in the minute range following physiological and environmental changes which influence ethylene evolution. By this procedure ethylene kinetics can also be compared in absolute values independent of flow rate and plant chamber volume.     

Storage of Tomatoes in Low Oxygen Atmospheres Inhibits Ethylene Action and Polygalacturonase Activity

The effect of low concentrations of O₂ (1%) with or without the application of exogenous ethylene (10 l/l) on the production of endogenous ethylene, the activity of polygalacturonase (PG), and the ripening of tomato fruits during storage for three weeks at 20°C and four weeks at 10°C, followed by one week under ambient conditions (25°C) was studied. The internal ethylene concentration in the fruits stored under low O₂ at 10 or 20°C was low during storage and increased only when fruits were transferred to ambient conditions. The application of exogenous ethylene to fruits stored under low O₂ at 10 or 20°C did not induce autocatalytic ethylene synthesis. By contrast, the internal ethylene concentration of fruits stored in air was high at 20°C and somewhat lower at 10°C. Under low O₂ conditions, PG activity was low and the fruits remained firm and green throughout storage, whereas, during storage in the air, PG activity increased and the fruits softened and developed their characteristic red color.     

Ethylene from 2-keto-4-thiomethyl butyric acid: the Haber-Weiss reaction

2-Keto-4-thiomethyl butyric acid is cooxidized, with production of ethylene, by the xanthine oxidase reaction. Ethylene production was inhibited by either superoxide dismutase or catalase indicating an essential role for both O₂^? and H₂O₂. Ethylene production was dependent upon iron complexes, while a variety of other metals were found ineffective. At pH 7.8 ethylenediaminetetraacetate-iron was much more effective in facilitating ethylene production, in the xanthine oxidase system, than was diethylenetriaminepentaacetate-iron; yet these two chelates were equally effective in ethylene production dependent upon the Fenton reaction. pH was an important variable in determining the activity of iron chelates in facilitating ethylene production in the xanthine oxidase system. The effectiveness of hydroxyl radical scavengers, in preventing ethylene production, was directly related to their abilities to scavenge OH · and this was the case in the presence of any of the several chelating agents tested. The proximal oxidant, responsible for ethylene production, thus appears to be OH ·, rather than some metal-oxy complex.     

Effects of ethylene on somatic embryogenesis and galanthamine content in <Emphasis Type="Italic">Leucojum aestivum</Emphasis> L. cultures

The influence of ethylene on in vitro morphogenesis of Leucojum aestivum and galanthamine accumulation was studied. Calli were cultivated on Murashige and Skoog (MS) medium supplemented with 25 μM 4-amino-3,5,6-trichloropicolinic acid (picloram) and 0.5 μM benzyladenine (BA). During incubation under these conditions, callus cultures produced ethylene (9.5 nL/g fresh weight: F.W.) whereas no ethylene was found in somatic embryos cultivated on medium supplemented with 0.5 μM α-naphthalene acetic acid (NAA) and 5 μM zeatin. Application of the precursor of ethylene 1-aminocyclopropane-1-carboxylic acid (ACC) increased ethylene production in both cultures, and decreased callus growth by a factor of 1.2, whereas callus growth was enhanced by a factor of 1.1 in the presence of an inhibitor of ethylene silver nitrate (AgNO₃) or by a factor of 1.2 with an absorbent potassium permanganate (KMnO₄). ACC enhanced the induction of somatic embryos and the development of globular embryos. Removal of ethylene by KMnO₄ during somatic embryogenesis led to the development of plants with greater length. Silver thiosulphate (STS) induced galanthamine production in callus cultures (0.1% dry weight), whereas ACC induced galanthamine production in somatic embryo cultures (2% dry weight).     

Effects of Low O(2) Root Stress on Ethylene Biosynthesis in Tomato Plants (Lycopersicon esculentum Mill cv Heinz 1350)

Low O₂ conditions were obtained by flowing N₂ through the solution in which the tomato plants (Lycopersicon esculentum Mill cv Heinz 1350) were growing. Time course experiments revealed that low O₂ treatments stimulated 1-aminocyclopropane-1-carboxylate (ACC) synthase production in the roots and leaves. After the initiation of low O₂ conditions, ACC synthase activity and ACC content in the roots increased and reached a peak after 12 and 20 hours, respectively. The conversion of ACC to ethylene in the roots was inhibited by low levels of O₂, and ACC was apparently transported to the leaves where it was converted to ethylene. ACC synthase activity in the leaves was also stimulated by low O₂ treatment to the roots, reaching a peak after 24 hours. ACC synthase levels were enhanced by cobalt chloride and aminooxyacetic acid (AOA), although they inhibited ethylene production. Cobalt chloride enhanced ACC synthase only in combination with low O₂ conditions in the roots. Under aeration, AOA stimulated ACC synthase activity in both the roots and leaves. However, in combination with low O₂ conditions, AOA caused a stimulation in ACC synthase activity in the leaves and no effect in the roots.     

Low levels of oxygen promote internodal elongation in floating rice independently of enhanced ethylene production

Submergence induces rapid elongation of internodes in floating rice(Oryza sativa L. cv. Habiganj Aman II). The initial signalfor such internodal elongation has been considered to be the reduced partialpressure of oxygen in submerged internodal cavities, which promotes theelongation of internodes through the enhancement of ethylene synthesis. Weexamined the relationship between low oxygen pressure and ethylene production inthe rapid elongation of floating rice internodes using ethylene biosynthesisinhibitors, aminooxyacetic acid (AOA) and CoCl₂. When floating ricestem segments were incubated in an atmosphere of low O₂, internodalelongation accelerated and ethylene production increased. However, in stemsegments treated with AOA or CoCl₂, low O₂ stillstimulated the elongation of internodes although the ethylene production by theinternodes was less than by those in control stem segments where internodalelongation was not promoted. These results indicate that low O₂ iscapable of causing rapid elongation of internodes of floating rice independentlyof enhanced production of ethylene. In addition to low O₂,submergence, ethylene and gibberellic acid each enhanced the production ofethylene by internodal tissues, suggesting that enhanced ethylene production isa common phenomenon accompanied by the acceleration of internodal elongation infloating rice.     

Ethylene based on woody biomass—what are environmental key issues of a possible future Swedish production on industrial scale

Purpose

In order to reduce its environmental impact, the chemical industry no longer produces base chemicals such as ethylene, solely from fossil, but also from biomass-based feedstocks. However, a biomass option suitable for one region might not be as suitable for another region due to, e.g., long transport and the related environmental. Therefore, local biomass alternatives and the environmental impact related to the production of chemicals from these alternatives need to be investigated. This study assesses the environmental impact of producing ethylene from Swedish wood ethanol.

Methods

The study was conducted following the methodology of life cycle assessment. The life cycle was assessed using a cradle-to-gate perspective for the production of 50,000 tonnes ethylene/year for the impact categories global warming, acidification (ACP), photochemical ozone creation, and eutrophication (EP).

Results and discussion

The production of enzymes used during the life cycle had a significant effect on all investigated impacts. However, reduced consumption of enzyme product, which could possibly be realized considering the rapid development of enzymes, lowered the overall environmental impact of the ethylene. Another approach could be to use alternative hydrolyzing agents. However, little information on their environmental impact is available. An additional key contributor, with regard to ACP, EP, and POCP, was the ethanol production. Therefore, further improvements with regard to the process’ design may have beneficial effects on its environmental impact.

Conclusions

The study assessed the environmental impact of wood ethylene and pointed to several directions for improvements, such as improved enzyme production and reduced consumption of enzyme products. Moreover, the analysis showed that further investigations into other process options and increase of ethylene production from biomass are worth continued research.     

The roles of carbon dioxide and abscisic acid in the production of ethylene

Since CO₂ is liberated in the conversion of ACC to ethylene, the evidence that ethylene production by plant tissues is actually promoted by CO₂ calls for an explanation. Accordingly, the formation of ethylene by oat (Avena sativa L. cv. Victory) leaves and by apple (Golden Delicious) and pear (Pyrus communis L. cv. Anjou) tissue in very low levels of CO₂ has been studied. The gas chromatograph was modified to measure CO₂ and ethylene at the same time, by reducing both to methane. (Response of the gas chromatograph to CO₂ concentrations is linear.) The work establishes a clear difference between the endogenous production of ethylene and its production from applied ACC, a difference which holds about equally for leaves and for fruit tissue. The difference is in the CO₂ requirement, namely, lowering the CO₂ level by 99% or more decreases the production of ethylene from applied ACC by 50–60%, but it does not decrease, or even slightly increases, its production from endogenous precursors. Thus, while the need for CO₂ has not been explained, it has at least been delimited. The responses to abscisic acid (ABA) also differ, but in the reverse direction, the endogenous production of ethylene being decreased up to 70% by ABA. while the liberation from ACC is promoted about 20%. ABA also promoted the respiratory CO₂ production by 30% or, in presence of 1-aminocyclopropane-1-carboxylic acid (ACC), by over 50%. Inhibition of ethylene production by cobalt or EDTA shows no such differentiation, while inhibition by Na catechol-4,6-disulfonate (Tiron) shows a small difference. It is concluded either that endogenous ethylene is formed by an enzyme system different from that reacting with ACC, or (more likely) that when ethylene arises from endogenous precursors the reaction does not proceed by way of free ACC, but by some activated form of it.     

Ethylene and in vitro rooting of rose shoots

Effects of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), ethylene biosynthesis inhibitor, (CoCl₂), and inhibitor of ethylene binding to receptors, 1-methylcyclopropene (1-MCP), on ethylene production and rooting in shoot culture of Rosa hybrida L. cv. Alba meidiland were studied. Additionally, effect of ethylene removal by KMnO₄ and HgClO₄ on rooting was tested. ACC increased ethylene production and delayed root formation, decreased the number of roots per shoot and inhibited root growth. In contrast, inhibition of ethylene production by CoCl₂ accelerated root emergence, and increased the number of roots per shoot. Likewise, removing ethylene from the ambient atmosphere improved root emergence and, increased root number of per shoot and markedly inhibited root growth. Blocking the ethylene receptors by 1-MCP increased ethylene level in the ambient atmosphere and increased both emergence and root formation. Both ethylene biosynthesis and action are involved in the control of rooting. Ethylene concentration in glass jars was too high for root emergence and formation, but was appropriate for root growth. CoCl₂ or 1-MPC can be recommended for regulation of rooting in rose shoot culture, since both emergence and number of roots were improved but root growth was not inhibited.     

Ethylene perception inhibitor 1-MCP decreases oxidative damage of leaves through enhanced antioxidant defense mechanisms in soybean plants grown under high temperature stress

Ethylene is a stress hormone involved in early senescence and abscission of vegetative and reproductive organs under stress conditions. Ethylene perception inhibitors can minimize the impact of ethylene-mediated stress. The effects of high temperature (HT) stress during flowering on ethylene production rate in leaf, flower and pod and the effects of ethylene inhibitor on ethylene production rate, oxidative damage and physiology of soybean are not understood. We hypothesize that HT stress induces ethylene production, which causes premature leaf senescence and flower and pod abscission, and that application of the ethylene perception inhibitor 1-Methyl cyclopropene (1-MCP) can minimize HT stress induced ethylene response in soybean. The objectives of this study were to (1) determine whether ethylene is produced in HT stress; (2) quantify the effects of HT stress and 1-MCP application on oxidative injury; and (3) evaluate the efficacy of 1-MCP at minimizing HT-stress-induced leaf senescence and flower abscission. Soybean plants were exposed to HT (38/28 °C) or optimum temperature (OT; 28/18 °C) for 14 d at flowering stage (R2). Plants at each temperature were treated with 1-MCP (1 μg L⁻¹) gas for 5 h or left untreated (control). High temperature stress increased rate of ethylene production in leaves, flowers and pods, production of reactive oxygen species (ROS), membrane damage, and total soluble carbohydrate content in leaves and decreased photosynthetic rate, sucrose content, F_v/F_m ratio and antioxidant enzyme activities compared with OT. Foliar spray of 1-MCP decreased rate of ethylene production and ROS and leaf senescence traits but enhanced antioxidant enzyme activities (e.g. superoxide dismutase and catalase). In conclusion, HT stress increased ethylene production rates, caused oxidative damage, decreased antioxidant enzyme activity, caused premature leaf senescence, increased flower abscission and decreased pod set percentage. Application of 1-MCP lowered ethylene and ROS production, enhanced antioxidant enzyme activity, increased membrane stability, delayed leaf senescence, decreased flower abscission and increased pod set percentage. The beneficial effects of 1-MCP were greater under HT stress compared to OT in terms of decreased ethylene production, decreased ROS production, increased antioxidant protection, decreased flower abscission and increased pod set percentage.     

Antibiotic production by submerged culture ofMelanconis flavovirens (Otth) Wehm.

The pyrenomyceteMelanconis flavovirens under submerged cultivation produced antibiotics active against both bacteria and fungi. Glucose and corn-steep liquor were the best and N sources for the antibiotic production, respectively. Supplementation with Tween-80 and ethylene glycol stimulated both antifungal and antibacterial antibiotic production, whereas oleic acid only the antifungal one. Addition of K₂HPO₄ also showed a positive effect. The optimal conditions for fermentation of the antifungal component are given.     

Does light inhibit ethylene production in leaves?

The effect of light on the rate of ethylene production was monitored using two different techniques—leaf segments incubated in closed flasks versus intact plants in a flow-through open system. Three different plants were used, viz sunflower (Helianthus annuus), tomato (Lycopersicon esculentum), and soybean (Glycine max). Experiments were conducted both in the presence and absence of 1-aminocyclopropane-1-carboxylic acid (ACC).

The results obtained indicate that, in all three species studied, light strongly inhibits ethylene production when cut leaf segments are incubated in the presence of ACC in closed flasks. When ethylene measurements are made with ACC-sprayed intact plants using a continuous flow system, the effect of light on ethylene production is only marginal. In leaf segments of sunflower and soybean incubated only in distilled H₂O in closed flasks, light promotes ethylene production. In tomato, there is no difference between the rate of ethylene production between light and darkness under such conditions. When measurements are made with intact plants in a continuous flow system, the rate of ethylene production is almost identical in light and darkness, in the three plants studied.

It is concluded that the effect of light on cut leaf segments incubated in the presence of ACC in closed flasks can be attributed to the techniques used for these measurements. Light has little effect on ethylene production by intact plants in an open system.

     

Medium and genotype factors influencing shoot regeneration from cotyledonary explants of Chinese cabbage (Brassica campestris L. ssp. pekinensis)

Medium conditions for reliable shoot regeneration from cotyledonary explants of Chinese cabbage were examined. Maximum shoot regeneration was obtained in the presence of 5 mg/l BA and 0.5 mg/l NAA. Shoot induction was further improved by the addition of AgNO₃ as well as higher concentrations (1.2–1.6%) of agar in the regeneration medium. When 123 genotypes were tested, a large variation in regeneration frequency was observed, ranging from 95% to 0%. Shoot regeneration frequency was not related to origin and days to maturity of the genotypes. Ethylene production from cultured explants seemed to play an important role in shoot regeneration. Explants of highly responsive genotypes or if cultured on the medium solidified with a higher concentration of agar generally showed low levels of ethylene production. However, AgNO₃, which also enhanced shoot induction, resulted in an increase in ethylene production. The possible interaction between ethylene and shoot regeneration is discussed. Received: 26 September 1997 / Revision received: 6 March 1998 / Accepted: 20 March 1998     

Effects of anaerobiosis on ethylene production, respiration and flowering in iris bulbs

Ethylene production of iris bulbs (Iris hollandica cv. Ideal) was very low. When stored at 30°C, production was 12–20 pmol C₂H₄ (kg fresh weight)^?1 h^?1. Higher temperatures (35°C, 40°C) enhanced the ethylene production; a treatment with 40°C for ca 7 days caused a 3 times higher ethylene production than at 30°. During anaerobic storage (in 100% N₂) ethylene production was equal to that of control bulbs. When after a 7 day period of anaerobiosis the N₂ was replaced by air, a burstlike ethylene production was observed. Twenty-four h after the replacement, ethylene production was equal to control values again. The effects of this production of ethylene on mitochondrial respiration and flowering were investigated. When mitochondria were isolated immediately after the anaerobic treatment (before the enhanced ethylene production) alternative pathway capacity was not detectable, a situation also occurring in control bulbs. When mitochondria were isolated 24 h after the end of the anaerobiosis (after the ethylene burst) uninhibited respiration did not change significantly, but a capacity of the alternative pathway was observed. The increase in alternative pathway capacity after anaerobiosis was partly inhibited by 2,5-norbornadiene (NBD), an ethylene antagonist. Fermentation occurred during anaerobiosis: ethanol concentrations increased during the treatment and decreased when air was supplied. When bulbs were exposed to ethanol vapour the alternative pathway was induced but only when very high ethanol levels in the bulbs were reached. The amount of ethanol accumulated in the bulbs during a 7 day anaerobic treatment was far too low to explain the observed induction of alternative pathway capacity. Flowering percentages were enhanced after a 24 h treatment with ethylene and after a 7 day anaerobic treatment. NBD significantly inhibited the effect of exogenous ethylene and of anaerobiosis on flowering. Ethanol was not able to induce flowering. The burst-like production of ethylene after anaerobiosis probably is responsible for the effects on respiration and flowering.