Patterns of ehtylene production in senescing leaves

Changes in the patterns of ethylene production, chlorophyll content, and respiration were studied in relation to the senescence of intact leaves and leaf discs. The primary leaves of pinto bean, which abscise readily during natural senescence, and tobacco and sugar beet leaves, which do not abscise, were used. A decrease in the rate of ethylene production and respiration, during the slow phase of chlorophyll degradation, was observed in leaf-blade discs cut from mature leaves and aged in the dark. During rapid chlorophyll loss both ethylene production and respiration increased and then decreased. These climacteric-like patterns were shown by leaf discs of all three species. Discs taken from leaves that had been senescing on the plant also showed a climacteric-like rise in ethylene production but not in respiration, which decreased continuously with leaf age. Climacteric-like patterns in the rise of ethylene and respiration for leaf discs were also shown by the petioles of both bean and tobacco leaves. This indicates that the rise of ethylene and respiration is characteristic of the general process of senescence in leaves and is not restricted to the abscission process. In contrast to the ethylene-forming systems in climacteric fruits and many flowers, the one in leaves declines sharply in the early stages of senescence. The subsequent rise of ethylene production appears to be associated with the rapid phase of chlorophyll breakdown, and may indicate the final stage of the senescence process during which ethylene could be actively involved in inducing leaf abscission.     

Effects of exogenous ethylene on ethylene production in citrus leaf tissue

Exogenous ethylene stimulated ethylene production in intact citrus (Citrus sinensis L. Osbeck cv. “Washington Navel”) leaves and leaf discs following a 24-hour exposure. Studies with leaf discs showed that ethylene production decreased when ethylene was removed by aeration. The extent of stimulation was dependent upon the concentration of exogenous ethylene (1-10 microliters per liter). Silver ion blocked the autocatalytic effect of ethylene at concentrations of 0.5 millimolar and lower, but increased ethylene production at higher concentrations. The stimulating effect of ethylene resulted from the enhancement of both 1-aminocyclopropane-1-carboxylic acid (ACC) formation and the conversion of ACC to ethylene. Whereas autocatalysis was evident following 24 hours incubation, autoinhibition of wound- and mannitol-induced ethylene production was observed during the first 24-hour incubation. Ethylene treatment during this period resulted in a marked decrease in ACC levels and ethylene production rates. Furthermore, in leaf discs treated for 24 hours with ethylene, ethylene production rates increased greatly during the first 2 hours after removal of exogenous ethylene by aeration. This increase was eliminated if the discs were transferred to propylene instead of air, indicating that the autocatalytic effect of ethylene is counteracted by its autoinhibitory effect. It is suggested that autocatalysis involves increased synthesis of ACC synthase and the enzyme responsible for the conversion of ACC to ethylene, whereas autoinhibition involves suppression of the activity of these two enzymes.     

Exogenous Polyamines Stimulate Ethylene Synthesis by Soybean Leaf Tissues

Exogenous supply of spermine (Spm) markedly stimulated ethyleneevolution from intact soybean leaves of leaf discs, stronglyincreased the level of free 1-aminocyclopropane-1-carboxylicacid (ACC), and slightly stimulated ethylene forming-enzyme(EFE) activity Spm treatment also resulted in leaf epinastyand accelerated leaf senescence Ethylene stimulation was depressed,but not abolished, by light, and was suppressed by inhibitorsof ACC synthase and EFE activity Spermidine had a less pronouncedstimulatory effect on ethylene production whereas the diaminesputrescine and diaminopropane were without effect These resultscontrast with other reports indicating that di- and polyaminesinhibit ethylene biosynthesis in plants, and extend our previousresults on detached tobacco leaves exogenously treated withpolyamines Glycine max, ethylene, polyamines     

ACC Synthesis as the Activated Step Responsible for the Rise of Ethylene Production Accompanying Citrus Exocortis Viroid Infection in Tomato Plants

Ethylene production was stimulated during the period when systemic symptoms appeared in tomato plants infected with citrus exocortis viroid (CEV). Neither methionine nor S-adenosylmethionine increased ethylene production in leaf discs. In contrast, 1-aminocyclopropane-l-carboxylic acid (ACC) stimulated ethylene production notably. Whether viroid infection acted upon ACC production, its conversion to ethylene, or both, was studied by determining the time course of the concentration of ACC and its in vivo production and conversion rates. During early symptoms, ACC synthesis increased and then remained steady during the development of symptoms, but no difference in the capacity of conversion of ACC to ethylene between healthy and CEV-infected tissues was observed. This indicates that ethylene production in tomato leaves showing systemic symptoms to CEV is activated at the level of ACC production.     

The Role of 1-Aminocyclopropane-1-carboxylic acid in the Control of Low Temperature Induced Ethylene Production in Leaf Tissue of Phaseolus vulgaris L .

Ethylene production from leaf discs of dwarf bean (Phaseolausvulgaris L.) was less than 02 nl g^–1 h^–1 at 5 Cbut rapidly increased tenfold on transfer to 25 C. The lowethylene production at 5 C and the potential for overshootproduction on transfer to 25C were not associated with accumulationof the ethylene synthesis intermediate 1-aminocyclopropane-1-carboxylicacid (ACC). Addition of exogenous ACC to leaf discs incubatedat 5C increased ethylene production, while similarly incubatedleaf discs did not synthesize increasing amounts of endogenousACC until they were transferred to 25 C. The basis for theovershoot in ethylene production when leafdiscs were transferredfrom 5 to 25 C appears to reside in changes to the pathwayleading to the synthesis of ACC or an earlier intermediate inthe pathway of ethylene biosynthesis. Ethylene, 1-aminocyclopropane-l-carboxylic acid, Phuseolru vulgaris L., dwarf bean, temperature     

ACC synthase expression regulates leaf performance and drought tolerance in maize

Ethylene regulates entry into several types of plant developmental cell death and senescence programs besides mediating plant responses to biotic and abiotic stress. The response of cereals to conditions of drought includes loss of leaf function and premature onset of senescence in older leaves. In this study, ACC synthase ( ACS ) mutants, affecting the first step in ethylene biosynthesis, were isolated in maize and their effect on leaf function examined. Loss of ZmACS6 expression resulted in delayed leaf senescence under normal growth conditions and inhibited drought-induced senescence. Zmacs6 leaves continued to be photosynthetically active under both conditions indicating that leaf function was maintained. The delayed senescence phenotype associated with loss of ZmACS6 expression was complemented by exogenous ACC. Surprisingly, elevated levels of foliar chlorophyll, Rubisco, and soluble protein as well as improved leaf performance was observed for all Zmasc6 leaves, including young and fully expanded leaves which were far from initiating senescence. These observations suggest that ethylene may serve to regulate leaf performance throughout its lifespan as well as to determine the onset of natural senescence and mediate drought-induced senescence.     

Ethylene formation in sugar beet leaves: evidence for the involvement of 3-hydroxytyramine and phenoloxidase after wounding

Ethylene production by sugar beet (Beta vulgaris L.) leaf discs is inhibited by white (or red, >610 nm) light or by wounding. In contrast, in wounded leaf discs, ethylene production is stimulated by light. The effect of light on wounded leaf discs has been studied by using an in vitro system which mimics the loss of compartmentation in the wounded leaf. Chlorophyll-free extracts from sugar beet leaves stimulate the production of the superoxide free radical ion (as a prerequisite for ethylene formation) by illuminated chloroplast lamellae. The substance from the crude leaf extracts which is active in stimulating the production of the superoxide free radical ion has been identified as 3-hydroxytyramine (dopamine). Exogenous dopamine between 5 mum and 100 mum stimulates ethylene formation by illuminated chloroplast lamellae from methional. It also stimulates the production of the superoxide free radical ion, the formation of which apparently involves both a lamellar phenoloxidase and photosynthetic electron transport as a 1-electron donor, and is cyanide-sensitive.     

Induction of ethylene synthesis and lipid peroxidation in damaged or TMV-infected tobacco leaf tissues by light

The effect of light on ethylene and ethane production in damaged leaf tissues was investigated. When whole leaves of tobacco cv. Samsun NN were damaged with liquid nitrogen, the ethylene formation was the highest, if 100?% of leaves were injured and were kept in the light, the lowest when leaves after 100?% injury were kept in darkness. Ethane production (lipid peroxidation) could be detected only in damaged, but not in control leaves, and was much higher in light than in darkness. In addition, there was a strong degradation of chlorophyll of damaged leaves kept in light. In light aminoethoxy-vinylglycine (AVG) inhibited ethylene formation in control, non-damaged whole leaves effectively, but in leaves with 100?% damage the inhibitory effect was much weaker and similar to the effect of propyl gallate (PG), a free radical scavenger. Both AVG and PG treatments decreased ethylene formation by control leaf discs and discs with 100?% damage. Ethane production was significantly inhibited by PG and slightly by AVG in the case of 100?% damage. Tiron, another free radical scavenger gave similar results on leaf discs as PG did. Paraquat (methylviologen, Pq), as a photosynthesis inhibiting and reactive oxygen species (ROS) producing herbicide produced a large amount of ethylene and ethane in light but very small amount in darkness. In accordance, tobacco mosaic virus (TMV) infection on the necrotic host resulted in significantly larger amount of ethylene and ethane formation in light than in darkness. We conclude that ethylene and ethane production of damaged plant tissues is strongly induced by light and ROS that are involved in this induction.     

Effect of regurgitant from Leptinotarsa decemlineata on wound responses in Solanum tuberosum and Phaseolus vulgaris

The effect of regurgitant from Leptinotarsa decemlineata Say larvae on wound-induced responses was studied using two plant species, Solanum tuberosum L. and Phaseolus vulgaris L. Wounding of one leaf of intact S. tuberosum plants differentially affected ethylene production and activities of peroxidase and polyphenol oxidase. Only polyphenol oxidase activity was stimulated by wounding in both wounded and systemic leaves. Peroxidase activity was not affected by wounding. Wounding caused only a transient increase of ethylene production from wounded leaves. The application of regurgitant to wound surfaces stimulated ethylene production as well as activities of peroxidase and polyphenol oxidase in both wounded and systemic leaves. Wounding significantly enhanced ethylene production and polyphenol oxidase activity in wounded and systemic leaves of P. vulgaris . The application of regurgitant caused an amplification of ethylene production, peroxidase activity, and polyphenol oxidase activity, in both wounded and systemic leaves of bean plants. Several substances were tested for their role as possible endogenous signals in P. vulgaris . Hydrogen peroxide and methyl jasmonate appeared as potential local and systemic signals of ethylene formation in wounded bean plants. Local ethylene production in leaf discs was differentially affected by the regurgitant application in potato versus bean plants. While all tested concentrations of regurgitant caused stimulation of ethylene formation from potato leaf discs, ethylene production was completely inhibited by increasing concentrations of the regurgitant in bean leaf discs. Our data present evidence that ethylene may play an important role in the interaction between plants and herbivores at the level of recognition of a particular herbivore leading to specific induction of signalling cascades.     

Effect of wounding on ethylene biosynthesis and senescence of detached spinach leaves

Parameters of senescence and ethylene biosynthesis pathway were screened simultaneously in detached spinach leaves and leaf discs. Senescence was enhanced by application of 1-aminocyclopropane-1-carboxylic acid (ACC) and was retarded by amino-ethoxyvinylglycine (AVG). Evidence is presented showing that the bursts of both wound- and climacteric-like ethylene promoted senescence of detached leaves and leaf discs. This ethylene-enhanced leaf senescence was dependent on: (a) ethylene production rates in the tissue; (b) the degree of wounding. Wounding resulted in elevated levels of 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), which declined in advanced stages of senescence. The results suggest that wounding might be regarded as one of the primary events in the induction of the senescence syndrome in detached leaves and leaf discs, while ethylene is implicated as a regulator of the rate of the process.     

Quantitative relationships between osmotic potential amd epicotyl growth in Vigna radiata as affected by osmotic stress and cotyledon excision

Ethylene biosynthesis in leaf discs of tobacco ( Nicotiana tabacum L. cv. Xanthi), as measured by the conversion of L-[3,4-¹⁴C]-methionine to ¹⁴C₂H₄, was markedly inhibited by exogenous ethylene. This inhibition was accompanied by a decrease in total (free + conjugated) content of 1-aminocyclopropane-1-carboxylic acid (ACC), most of which appeared in its conjugated inactive form. The autoinhibitory effect of ethylene was reversible and could be relieved by Ag⁺. The Ag⁺-treated leaf discs, with or without ethylene, contained only free ACC at an increased level. The results suggest that in tobacco leaves, the autoinhibition of ethylene production resulted from reduction in the availability of free ACC, through both suppression of ACC formation and increased ACC conjugation.     

A Relationship between Membrane Permeability and Ethylene Production at High Temperature in Leaf Tissue of Phaseolus vulgaris L.

Leaf discs cut from primary leaves of Phaseolus vulgaris L cvMasterpiece were incubated at temperatures higher than the growthtemperature of 25 °C Both basal and wound ethylene productionincreased up to temperatures of 35–37 5 °C, thereafterdeclining rapidly There was no detectable ethylene productionat temperatures above 42 5 °C Exposure of leaf discs tohigh temperature for 60 mm resulted in a large production ofwound ethylene when they were returned to 25 °C The magnitudeof ethylene production was related to the initial incubationtemperature as was the length of the lag period before maximumproduction was achieved The results are discussed in relationto the requirement for continued membrane integrity for ethyleneproduction ethylene, temperature, membrane permeability, Phaseolus vulgaris L, dwarf bean     

Maintenance of photosynthetic capacity in flooded tomato plants with reduced ethylene sensitivity

Ethylene is considered one of the most important plant hormones orchestrating plant responses to flooding stress. However, ethylene may induce deleterious effects on plants, especially when produced at high rates in response to stress. In this paper, we explored the effect of attenuated ethylene sensitivity in the Never ripe (Nr) mutant on leaf photosynthetic capacity of flooded tomato plants. We found out that reduced ethylene perception in Nr plants was associated with a more efficient photochemical and non-photochemical radiative energy dissipation capability in response to flooding. The data correlated with the retention of chlorophyll and carotenoids content in flooded Nr leaves. Moreover, leaf area and specific leaf area were higher in Nr, indicating that ethylene would exert a negative role in leaf growth and expansion under flooded conditions. Although stomatal conductance was hampered in flooded Nr plants, carboxylation activity was not affected by flooding in the mutant, suggesting that ethylene is responsible for inducing non-stomatal limitations to photosynthetic CO₂ uptake. Upregulation of several cysteine protease genes and high protease activity led to Rubisco protein loss in response to ethylene under flooding. Reduction of Rubisco content would, at least in part, account for the reduction of its carboxylation efficiency in response to ethylene in flooded plants. Therefore, besides its role as a trigger of many adaptive responses, perception of ethylene entails limitations in light and dark photosynthetic reactions by speeding up the senescence process that leads to a progressive disassembly of the photosynthetic machinery in leaves of flooded tomato plants.     

Ethylene evolution from various developing organs of olive (Olea europaea) after excision

Ethylene evolution from leaves, stems, inflorescences and fruits of the olive plant ( Olea europaea L.) cv. Manzanillo was studied at various stages of their development. Mature non-growing organs, particularly leaves, have a constant, low, and uniform rate of ethylene evolution. Ethylene evolution from detached mature olive leaves was constant during the first 12 h after excision. Leaves on shoots maintained in vitro kept a constant rate of ethylene evolution for at least the first 5–6 days. Leaf injury significantly increased ethylene evolution. Ethylene evolution from injured and non-injured control leaves could be markedly inhibited aminoethoxyvinylglycine (AVG) applied to the leaves or fed to the shoot. The use of excised olive shoots and leaves as an in vitro model system for studies of induced metabolic processes such as abscission and developing water stress was suggested.     

Ozone-induced ethylene production is dependent on salicylic acid,and both salicylic acid and ethylene act in concert to regulate ozone-induced cell death

Ethylene is known to influence plant defense responses including cell death in response to both biotic and abiotic stress factors. However, whether ethylene acts alone or in conjunction with other signaling pathways is not clearly understood. Ethylene overproducer mutants, eto1 and eto3, produced high levels of ethylene and developed necrotic lesions in response to an acute O3 exposure that does not induce lesions in O3-tolerant wild-type Col-0 plants. Treatment of plants with ethylene inhibitors completely blocked O3-induced ethylene production and partially attenuated O3-induced cell death. Analyses of the responses of molecular markers of specific signaling pathways indicated a relationship between salicylic acid (SA)- and ethylene-signaling pathways and O3 sensitivity. Both eto1 and eto3 plants constitutively accumulated threefold higher levels of total SA and exhibited a rapid increase in free SA and ethylene levels prior to lesion formation in response to O3 exposure. SA pre-treatments increased O3 sensitivity of Col-0, suggesting that constitutive high SA levels prime leaf tissue to exhibit increased magnitude of O3-induced cell death. NahG and npr1 plants compromised in SA signaling failed to produce ethylene in response to O3 and other stress factors suggesting that SA is required for stress-induced ethylene production. Furthermore, NahG expression in the dominant eto3 mutant attenuated ethylene-dependent PR4 expression and rescued the O3-induced HR (hypersensitive response) cell death phenotype exhibited by eto3 plants. Our results suggest that both SA and ethylene act in concert to influence cell death in O3-sensitive genotypes, and that O3-induced ethylene production is dependent on SA.     

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.

     

The effect of plant cytokinin hormones on the production of ethylene, nitric oxide, and protein nitrotyrosine in ageing tobacco leaves

Transgenic plants with genetically increased or decreased levels of cytokinins were used to investigate the effect of cytokinin level on the production of ethylene, a plant hormone with suggested role in senescence, and the production of nitric oxide, potentially important signalling and regulatory molecule. The production of these gases was followed during the course of leaf development and senescence. The production of ethylene and nitric oxide is under genetic control of genes other than those involved in regulation of senescence. The difference in basic ethylene and NO levels in different tobacco cultivars was higher than their changes in senescence. The results of this study did not indicate a direct link between ethylene production and cytokinin levels. However, there was a decreased production of NO in senescent leaves. Low cytokinins level was associated with increased NO production during leaf development. Protein nitrotyrosine proved to be a better indicator of the reactive nitrogen species than measuring of the NO production. Higher nitrotyrosine concentrations were found in insoluble proteins than in the soluble ones, pointing to membrane proteins as the primary targets of the reactive nitrogen species. In plants with elevated cytokinin levels the content of nitrated proteins decreased both in soluble and insoluble fractions. This finding indicates an antioxidative function of cytokinins against reactive nitrogen species.     

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.     

Biogenic ethylene promotes seedling emergence from the sediment seed bank in an ephemeral tropical rock pool habitat

Background and aims

Ethylene has been increasingly implicated as a regulatory mechanism in plant germination, growth, and development, and is produced from the sediments of freshwater habitats. In this paper, we analyse the production and origin of ethylene from ephemeral freshwater rock pool sediments, and explore the role of ethylene in regulating seedling emergence from the seed bank.

Methods

The production of ethylene from rock pool sediments subjected to variable moisture content and antibiotic treatments was assessed through gas chromatography, and the role of ethylene in regulating seedling emergence was determined by seedling emergence assays and seed germination experiments.

Results

Biogenic ethylene production from rock pool sediments occurred rapidly (3–6 h) following inundation, with the majority of seedling emergence occurring between 36 and 72 h. Inoculation of sediments with streptomycin and amphotericin B resulted in significantly reduced ethylene production (up to 60 % and 84 % respectively), and completely inhibited seedling emergence. Additionally, the exposure of dormant seeds to ethylene resulted in significantly increased seed germination percentage in five out of six rock pool species.

Conclusions

Biogenic ethylene production may play an important role in regulating seed dormancy and the timing of seedling emergence from the sediment seed bank following inundation events in rock pools and other freshwater aquatic communities.     

Calcium Requirement for Ethylene-Dependent Responses

Ethylene, a gaseous plant hormone, plays a role in plant development, defense, and climacteric fruit ripening. Both genetic and biochemical evidence suggest that the response of plants to ethylene is mediated by a specific ethylene receptor. The signal emanating from the receptor-effector complex is then presumably transduced via an unknown cascade pathway. We have used the plant pathogenesis response, exemplified by the induction of the pathogenesis-related gene chitinase, as a paradigm to investigate ethylene-dependent signal transduction in the plant cell. We showed that calcium is necessarily involved in the ethylene-mediated pathogenesis response. Blocking calcium fluxes with chelators inhibited ethylene-dependent induction of chitinase accumulation, but not ethylene independent induction. Artificially increasing cytosolic calcium levels by treatments with the calcium ionophore ionomycin or the calcium pump blocker thapsigargin stimulated chitinase accumulation. Plants grown in calcium-poor soil showed a 10-fold reduction in leaf extractable calcium. Their leaves exhibited a reduced pathogenesis reaction to ethylene and were impaired in another hormone response mediated by calcium, i.e., abscisic acid-controlled closure of guard cells. The addition of calcium to leaves excised from calcium-deficient plants restored their sensitivity to ethylene. Ethylene participates in the control of seedling growth, promoting the so-called "triple response" that results in distinct morphological development, such as hypocotyl hook formation. This effect, similar to the ethylene-promoted pathogenesis response, was found to be calcium dependent. The results indicate that calcium is required for a variety of ethylene-dependent processes.