Ethylene Evolution following Treatment with 1-Aminocyclopropane-1-carboxylic Acid and Ethephon in an in Vitro Olive Shoot System in Relation to Leaf Abscission

1-Aminocyclopropane-1-carboxylic acid (ACC) supplied via the cut base of detached olive shoots caused a burst of ethylene from leaves, but other cyclopropanes tested did not exhibit this effect. Ethephon (ET) and another ethylene-releasing compound caused a prolonged increase in ethylene evolution. ACC had only a very limited effect on leaf abscission regardless of concentration, whereas shoots placed with cut bases in ET for 60 to 80 minutes exhibited 100% leaf abscission within 90 hours. Shoots with inflorescences treated with ET just prior to anthesis began to wilt in vitro within 20 to 30 hours and failed to exhibit leaf abscission. At earlier stages of development, ET induced more leaf abscission on reproductive shoots than on vegetative shoots. It is suggested that the duration of ethylene evolution from the leaves governs their potential for abscission and that bursts of ethylene evolution even though large in amount may not induce abscission.     

Ethylene Production by Attached Leaves or Intact Shoots of Tobacco Cultivars Differing in Their Speed of Yellowing during Curing

Using an open air flow system, differences in the yellowing rate of leaves during curing were assessed in relation to ethylene production by shoots of intact seedlings or attached mature leaves of 60 day old tobacco (Nicotiana tabacum L.) plants. The rate of ethylene evolution from the leaves of the fast yellowing cultivars was significantly higher than in the slow yellowing ones. The same differences were obtained with shoots of intact seedlings. The findings suggest that it is possible to use ethylene production by seedlings as a selection criterion in screening for genotypic differences in the rate of yellowing. The ability of carbon dioxide (1%) to enhance ethylene production by attached leaves was significant in a slow, but not in a fast yellowing cultivar. However, similar amounts of ethylene were produced on administration of 1-aminocyclopropane-1-carboxylic acid to a slow and a fast yellowing cultivar. Exposure of attached leaves to exogenous ethylene (0.1 microliter per liter) accelerated the loss of chlorophyll and protein. This treatment was effective only for slightly yellow leaves and not for fully expanded green ones. The significance and possible use of ethylene in the flue-curing process are discussed.     

Ethylene enhances shoot formation in cultures of the peach rootstock GF-677 (Prunus persica x P. amygdalus)

The influence of ethylene on shoot formation from GF-677 (Prunus persica × P. amygdalus) shoot tip explants was studied in vitro. Cultures in test tubes were placed inside 5 1 glass jars and supplemented with various ethylene concentrations (0–10 ppm). Ethylene at 0.1 ppm, applied during the first 2 weeks of culture, increased the number and the length of shoots produced in vitro. Test tubes with cultures sealed with various types of closure accumulated in their atmosphere different levels of ethylene ranging from 0.1 to 1.2 ppm, depending on the type of closure. Test tubes with cotton-wool bungs had the least while those with serum stoppers had the highest amount of ethylene. The maximum number of shoots was recorded in test tubes covered with serum stoppers. The ethylene concentration was related linearly (R=0.974) to the shoot number and exponentially (R=0.975) to the shoot length.Abbreviations BA benzyladenine - IAA indoleacetic acid - HSD honestly significant difference     

Evolution of ethylene by sulphur dust addition

Kidney-bean plants ( Phaseolus vulgaris L. cv. Contender) were dusted with sulphur 25 days after germination. The amount of ethylene evolution was measured in shoots (with attached leaves) and roots from plants in several stages of development. The growth of shoots and roots was also measured, and the flowering time observed. The ethylene evolution was associated with precise morphogenic stages. The amounts of ethylene produced from sulphur treated plants, compared with that evolved from control plants, showed two stages of stimulation in shoots, one preceding full bloom and one preceding fruit-set. Inhibition of ethylene evolution due to sulphur dust occurred in roots before initiation of floral primordia and before full bloom. The treatment with sulphur dust seemed to increase the number of leaves per plant, but only in the vegetative stage. Likewise, the earliness of flowering was enhanced. The effects of elemental sulphur dust treatments on ethylene evolution may be attributed to a slow oxidation of elemental sulphur in air producing SO²; this SO² greatly enhances ethylene evolution from leaf tissues.     

Light Stimulation of Ethylene Release from Leaves of Gomphrena globosa L

The effect of light and CO₂ on both the endogenous and 1-aminocyclopropane-1-carboxylic acid (ACC)-dependent ethylene evolution from metabolically active detached leaves and leaf discs of Gomphrena globosa L. is reported. Treatment with varying concentrations of ACC did not appear to inhibit photosynthesis, respiration, or stomatal behavior. In all treatments, more ethylene was released into a closed flask from ACC-treated tissue, but the pattern of ethylene release with respect to light/dark/CO₂ treatments was the same.

Leaf tissue in the light with a source of CO₂ sufficient to maintain photosynthesis always generates 3 to 4 times more ethylene than tissue in the dark. Conversely, the lowest rate of ethylene release occurs when leaf tissue is illuminated and photosynthetic activity depletes the CO₂ to the compensation point. Ethylene release in the dark is also stimulated by CO₂ either added to the flask as bicarbonate or generated by dark respiration. Ethylene release increases dramatically and in parallel with photosynthesis at increasing light intensities in this C₄ plant. Ethylene release appears dependent on CO₂ both in the light and in the dark. Therefore, it is suggested that the important factor regulating the evolution of ethylene gas from leaves of Gomphrena may be CO₂ metabolism rather than light per se.

     

Nitrogen fertility and leaf age effect on ethylene production of cotton in a controlled environment

The effect of nitrogen (N) fertility and its subsequent impact on ethylene production varies with plant species. Additionally, ethylene production reportedly increases or decreases with leaf age for several species. We examined leaf age and N fertility effects on ethylene production of cotton (Gossypium hirsutum L.) during the early vegetative stages of development (14 to 42 days after emergence) in a controlled environment. Ethylene production was determined by sampling leaf discs from the topmost fully expanded, middle, and bottom leaves of the canopy at 14, 21, 28, 35, and 42 days after emergence. Ethylene was collected from leaf discs in sealed test tubes and quantified by gas chromatography. Early in development, a N deficiency was associated with elevated levels of ethylene, suggesting stress ethylene production was occurring in response to a N-deficiency stress. As plant development progressed, however, increased ethylene production was associated with higher levels of applied N. Additionally, higher ethylene production was linearly associated with higher chlorophyll levels in all three leaves sampled. Ethylene production within plants receiving any given rate of N initially increased and then decreased with leaf age. The dynamics of this relationship suggest that as the N status of the plant changes during plant development, the relative rate of ethylene production, with regard to leaf age, is significantly influenced.     

Circadian Ethylene Synthesis in <Emphasis Type="Italic">Sorghum bicolor</Emphasis>: Expression and Control of the System at the Whole Plant Level

Ethylene production by sorghum is rhythmic and the amplitude of the rhythm is increased both by dim, far-red enriched light and in mutant plants deficient in phytochrome B. The mechanisms involved in controlling ethylene production were examined in detail by measuring the rate of ethylene production among organs and tissues, examining the organ-specific levels of ACC (1-aminocyclopropane-1-carboxylic acid, the ethylene precursor) and investigating the contribution of the roots to shoot ethylene production. The results demonstrate that the expanding leaves were the major source of ethylene under dim, far-red enriched light and in the phytochrome B mutant. Enhanced ethylene production by the expanding leaf appeared to be the result of targeted delivery of ACC to this tissue. Root ACC levels were much higher than those in the shoot but roots converted much less of this endogenous ACC to ethylene. Applying ACC to the roots had only a marginal effect on their ethylene production, but greatly increased that of the shoots. Decapitated shoots continued to produce ethylene in a rhythmic pattern but the amplitude decreased with time compared to intact plants. The results collectively suggest that some, but not all, of the shoot ethylene rhythm depends on the transport of ACC from the roots to the shoots.     

Physiological responses of resistant and susceptible plants to diclofop-methyl and its antagonism by 2,4-D and antioxidants

Diclofop-methyl (DM) sprayed onto 6–8-week-old plants of leafy spurge ( Euphorbia esula L.) caused senescence and abscission of older leaves, while the young leaves and apex remained attached. The phytotoxicity of DM was reversed by the antioxidant, α -tocopherol (vitamin E), in leafy spurge and DM-susceptible oat ( Avena sativa L. cv. Gary). DM and 2,4-dichlorophenoxyacetic acid (2,4-D) increased ethylene evolution in mature leaves of leafy spurge. Vitamin E reduced the DM-induced ethylene by ampproximately 50%, but had no effect on the 2,4-D-induced ethylene. DM did not increase ethylene in DM-resistant pea or tobacco, but 2,4-D induced a 3-fold increase in ethylene evolution over controls in DM-resistant tobacco. 2,4-D amppears to act at a site different from that of DM in the pathway of ethylene formation. Ethylene evolution increased in DM-treated susceptible biotypes of annual ryegrass ( Lolium rigidum L.) and wild oat ( Avena fatua L.), but not in resistant biotypes of these species. DM reduced root and shoot formation and dry weight in hypocotyl segments of etiolated leafy spurge seedlings grown in vitro. Organogenesis and dry weights were increased by the combination of DM+antioxidants. Vitamin E was a more effective antioxidant than ascorbic acid. These results sumpport the hypothesis that DM induces oxidative stress in susceptible plant tissues and that antioxidants reduce the damaging action of the phytotoxic free radicals.     

Diurnal Fluctuations in Ethylene Formation in Chenopodium rubrum

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

Ethylene Production and Action during Foliage Senescence in Hedera helix L.

Detached leaves of Hedera helix remained green in the dark for20 d. Exogeneous ethylene increased respiration, endogeneousethylene biosynthesis and non-protein ninhydrin-positive compounds,while promoting losses of chlorophyll and sucrose. The sensitivityof the leaves to exogenous ethylene (1–100 mm³ dm^-3) variedgreatly with time of year. Ethylene treatment increased ADP,ATP, UDP and GTP appreciably but had no effect on other nucleotides.Leaves senescing naturally on the parent plant increased theirrates of ethylene evolution and oxygen uptake. These resultssupport the view that endogenous ethylene plays an integralpart in the senescence of detached and attached ivy leaves. Key words: Ethylene, leaves, senescence, nucleotides     

Ethylene Evolution Stimulated by Succimc Acid-2,2-Dimethylhydrazide in Apple Shoots

The rate of ethylene production in the shoot tips of the apple cultivar ‘Ingrid Marie’ (Red motant) after succinic acid-2,2-dimethylhydrazide (SADH) treatment was investigated. The shoots were treated with SADH at 12.5, 25 or 50 mM in the months of June, July and August. The samples were analysed 7,15, 30 and 60 days after SADH spray. Ethylene production was considerably higher in the SADH-treated shoots than in the untreated ones. Application of 12.5 or 25mMSADH late in June stimulated ethylene production 3-fold, while 50 mM produced a 5-fold increase in ethylene production 7 days after spraying. There was a continuous decrease in ethylene production at the subsequent samplings. In untreated control shoots there was a slight increase. However, even 60 days after spraying the shoots treated with 50 mM had higher ethylene production than the control shoots. The same relationship was found in the shoots treated in the months of July and August. A parallelism has been established between the rate of ethylene production and growth retardation, A residual effect of SADH treatment in earlier years was demonstrated and is discussed.     

Suppression and promotion of growth by ethylene in rice seedlings depends on ambient humidity

We examined the effect of ethylene on the growth of rice seedlings (Oryza sativa L.) at various degrees of humidity. Ethylene significantly suppressed the growth of shoots when applied to seedlings grown under 30% relative humidity (RH), but promoted the growth of shoots when applied to seedlings grown under 100% RH. The application of gibberellic acid (GA₃) promoted the elongation of shoots in seedlings grown under 30% and 100% RH. Ethylene inhibited the shoot elongation induced by GA₃ at 30% RH, but enhanced the elongation induced by GA₃ at 100% RH. These results indicate that ethylene can either promote or suppress the growth of rice shoots depending on ambient humidity, and that these actions of ethylene may be mediated through modulating the responsiveness of shoots to gibberellin.     

Promotion of petunia (Petunia hybrida L.) regeneration in vitro by ethylene

The influence of ethylene on shoot and root formation from petunia leaf explants was studied in cultures in test tubes placed in 51 glass jars. Reduction of the endogenously produced ethylene by inclusion of ethysorb (KMnO₄), an ethylene absorbent, caused a decrease of the number of shoots. On the other hand, supplementing the cultures with ethylene (0.01–10 ppm) caused a marked increase of the number of shoots without, however, any effect on the length and fresh weight. Ethylene treatments (1 ppm) were found to be most effective when they were applied in the second week of culturing of petunia explants. Addition of Co⁺⁺ to the medium resulted in a reduction of the endogenously produced ethylene and concomitantly reduced shoot formation. Similarly, inclusion of Ag⁺, an inhibitor of ethylene action, resulted in poor shoot formation. Ethylene also appeared to play a role on rooting of petunia microshoots in vitro in an auxin-free medium. Ethylene at a concentration of 10 ppm induced adventitious root formation considerably, whereas at low levels (0.01–1 ppm) it had no influence on rooting.     

The effect of the gaseous state on bud induction and shoot multiplication in vitro in eastern white cedar

The effect of vessel type and the gaseous phase on the morphogenic response of Thuja occidentalis L. explants in vitro was studied. Explants were cultured in container types that varied in their degree of gas exchange. Traps for ethylene and CO₂ were employed. During shoot bud induction from embryonic explants, the number and elongation of shoot buds improved significantly when gastight, serum-capped flasks were used compared to the foam bung-capped flasks or the regularly used Petri dishes. Elimination of the two gases from the headspace of the flasks either singly or together reduced shoot bud induction and especially elongation of shoots. A similar response was seen during axillary bud development from cultured shoots. Ethylene and CO₂ accumulation promoted development and elongation of axillary shoots. An increase in the zeatin concentration in the medium produced a greater number of axillary shoots and higher levels of ethylene in the culture vessels. Removal of CO₂ caused gradual death of the shoots, while removal of ethylene alone reduced axillary shoot lengths significantly. Inclusion of aminoethoxyvinylglycine in the medium combined with ethylene traps produced an effect similar to the use of ethylene traps alone.     

Ethylene-induced leaf senescence depends on age-related changes and OLD genes in Arabidopsis

Ethylene can only induce senescence in leaves that have reached a defined age. Thus, ethylene-induced senescence depends on age-related changes (ARCs) of individual leaves. The relationship between ethylene and age in the induction of leaf senescence was tested in Arabidopsis Ler-0, Col-0, and Ws-0 accessions as well as in eight old (onset of leaf death) mutants, isolated from the Ler-0 background. Plants with a constant final age of 24 d were exposed to ethylene for 3-16 d. The wild-type accessions showed a common response to the ethylene treatment. Increasing ethylene treatments of 3-12 d caused an increase in the number of yellow leaves. However, an ethylene exposure time of 16 d resulted in a decrease in the amount of yellowing. Thus, ethylene can both positively and negatively influence ARCs and the subsequent induction of leaf senescence, depending on the length of the treatment. The old mutants showed altered responses to the ethylene treatments. old1 and old11 were hypersensitive to ethylene in the triple response assay and a 12-d ethylene exposure resulted in a decrease in the amount of yellow leaves. The other six mutants did not show a decrease in yellow leaves with an ethylene treatment of 16 d. The results revealed that the effect of ethylene on the induction of senescence can be modified by at least eight genes.     

Hormonal control of root development on epiphyllous plantlets of Bryophyllum (Kalanchoe) marnierianum: role of auxin and ethylene

Epiphyllous plantlets develop on leaves of Bryophyllum marnierianum when they are excised from the plant. Shortly after leaf excision, plantlet shoots develop from primordia located near the leaf margin. After the shoots have enlarged for several days, roots appear at their base. In this investigation, factors regulating plantlet root development were studied. The auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA) abolished root formation without markedly affecting shoot growth. This suggested that auxin transport from the plantlet shoot induces root development. Excision of plantlet apical buds inhibits root development. Application of indole-3-acetic acid (IAA) in lanolin at the site of the apical buds restores root outgrowth. Naphthalene acetic acid (NAA), a synthetic auxin, reverses TIBA inhibition of plantlet root emergence on leaf explants. Both of these observations support the hypothesis that auxin, produced by the plantlet, induces root development. Exogenous ethylene causes precocious root development several days before that of a control without hormone. Ethylene treatment cannot bypass the TIBA block of root formation. Therefore, ethylene does not act downstream of auxin in root induction. However, ethylene amplifies the effects of low concentrations of NAA, which in the absence of ethylene do not induce roots. Ag(2)S(2)O(3), an ethylene blocker, and CoCl(2), an ethylene synthesis inhibitor, do not abolish plantlet root development. It is therefore unlikely that ethylene is essential for root formation. Taken together, the experiments suggest that roots develop when auxin transport from the shoot reaches a certain threshold. Ethylene may augment this effect by lowering the threshold and may come into play when the parent leaf senesces.     

Intact Leaves Exhibit a Climacteric-Like Rise in Ethylene Production before Abscission

The rate of ethylene production by intact, attached leaves of cotton plants (Gossypium hirsutum L.) during aging and senescence was studied using a continuous flow system that allowed air around enclosed leaves to be scrubbed to collect and assay ethylene. Senescence of lower leaves began around 150 d after planting in a controlled environment room. A progressive decline in the ethylene production rate was observed when comparing the 3rd, 6th, and 10th leaves from the base with each other. Ethylene production rates of individual leaves also declined over a 50-d period. However, as leaves began to appear chlorotic, a peak of ethylene production occurred that lasted for about 4 d followed by abscission. This peak involved a 3-fold or greater increase in the rate of ethylene production. The data indicate that intact leaves experience a climacteric-like surge in ethylene production after visible symptoms of senescence appear. This “ethylene climacteric” is apparently the signal that initiates hydrolysis of cell walls in the abscission zone.     

Do Polyamines Participate in the Long-Distance Translocation of Stress Signals in Plants?

Accumulation and ethylene-dependent translocation of free polyamines was studied in various organs, the phloem and xylem exudates of common ice plants (Mesembryanthemum crystallinum L.). Under normal conditions (23–25°C), spermidine predominated among polyamines. Cadaverine was found in old leaves, stems, and, in large quantities, in roots. The heat shock treatment (HS; 47°C, 2 h) of intact plant shoots induced intense evolution of ethylene from leaves but reduced the leaf content of polyamines. Under these conditions, the concentration of polyamines in roots, particularly of cadaverine, increased many times. The HS treatment of roots (40°C, 2 h) induced translocation of cadaverine to stems and putrescine to leaves. An enhanced polyamine content after HS treatment was also found in the xylem and phloem exudates. The exposure of detached leaves to ethylene led to a reduction in their putrescine and spermidine and accumulation of cadaverine, which implies the ethylene-dependent formation of cadaverine and a possible relation between the HS-induced translocation of this diamine to roots and the transient ethylene evolution by leaves. To validate this hypothesis, we compared the ethylene evolution rate and interorgan partitioning of cadaverine and other polyamines for two lines of Arabidopsis thaliana: the wild type (Col-0) and ein4 mutant with impaired ethylene reception. In plants grown in light at 20–21°C, the rate of ethylene evolution by rosetted leaves was higher in the mutant than in the wild type. The content of putrescine and spermidine was reduced in mutant leaves, whereas cadaverine concentration increased almost threefold compared with the wild type. In roots, cadaverine was found only in the wild type and not in the mutant line. Our data indicate the ethylene-dependent formation of cadaverine in leaves and possible involvement of cadaverine and ethylene in the long-distance translocation of stress (HS) signal in plants.     

Heterotrophic nitrogen fixation (acetylene reduction) associated to flooded rice: A modified measurement technique in the field

A modifiedin situ technique for measuring heterotrophic nitrogen fixing (acetylene reducing) activity associated to rice is proposed. Ethylene evolution rates measured in opaque cylinders covering the stems of rice plants which have been cut 10 cm over the water level were found independent of the diurnal cycle. Cutting of the leaves resulted in decreased variation between plants and suppression of the acceleration of ethylene evolution rate after 12 h incubation as compared to intact plants. In both systems ethylene evolved was swept by a current of methane and the molar ratio between methane and ethylene was stabilized after 12 h. Methane evolution rates remained stable during 12 h and more than 24 h in whole plants and cut plants respectively. It is suggested that alteration in the active gas transport system after 12 h incubation under 10% acetylene may lead to erroneous evaluation of the actual ethylene production in the root's environment. The average values of ethylene evolution rates by cut plants between 12 and 24 h of incubation may be used for comparative studies of nitrogen fixing activity associated to flooded rice.     

Involvement of ethylene in the action of the cotton defoliant thidiazuron

The effect of the defoliant thidiazuron (N-phenyl-N′-1,2,3-thiadiazol-5-ylurea) on endogenous ethylene evolution and the role of endogenous ethylene in thidiazuron-mediated leaf abscission were examined in cotton (Gossypium hirsutum L. cv Stoneville 519) seedlings. Treatment of 20- to 30-day-old seedlings with thidiazuron at concentrations equal to or greater than 10 micromolar resulted in leaf abscission. At a treatment concentration of 100 micromolar, nearly total abscission of the youngest leaves was observed. Following treatment, abscission of the younger leaves commenced within 48 hours and was complete by 120 hours. A large increase in ethylene evolution from leaf blades and abscission zone explants was readily detectable within 24 hours of treatment and persisted until leaf fall. Ethylene evolution from treated leaf blades was greatest 1 day posttreatment and reached levels in excess of 600 nanoliters per gram fresh weight per hour (26.7 nanomoles per gram fresh weight per hour). The increase in ethylene evolution occurred in the absence of increased ethane evolution, altered leaf water potential, or decreased chlorophyll levels. Treatment of seedlings with inhibitors of ethylene action (silver thiosulfate, hypobaric pressure) or ethylene synthesis (aminoethoxyvinylglycine) resulted in an inhibition of thidiazuron-induced defoliation. Application of exogenous ethylene or 1-aminocyclopropane-1-carboxylic acid largely restored the thidiazuron response. The results indicate that thidiazuron-induced leaf abscission is mediated, at least in part, by an increase in endogenous ethylene evolution. However, alterations of other phytohormone systems thought to be involved in regulating leaf abscission are not excluded by these studies.