Induction Of Ethylene Synthesis Research Articles

Role of Melatonin in Apple Fruit during Growth and Ripening: Possible Interaction with Ethylene.

The role of melatonin during the growth and ripening of apple fruit was studied using local varieties. The evolution of the growth and ripening parameters, including fruit size and weight, firmness, color change, sugar content, and ethylene production, was different in the five varieties studied, with yellow apples (Reineta and Golden) initiating the ripening process earlier than reddish ones (Teórica, Sanroqueña, and Caguleira). Changes in the melatonin and melatonin isomer 2 contents during growth and ripening were studied in Golden apples, as was the effect of the melatonin treatment (500 µM, day 124 post-anthesis) on the apple tree. Melatonin content varied greatly, with higher value in the skin than in the flesh. In the skin, melatonin increased at day 132 post-anthesis, when ethylene synthesis started. In the flesh, melatonin levels were high at the beginning of the growth phase and at the end of ripening. Melatonin isomer 2 was also higher once the ripening started and when ethylene began to increase. The melatonin treatment significantly advanced the ethylene production and increased the fruit size, weight, sugar content, and firmness. The data suggest that melatonin stimulates fruit ripening through the induction of ethylene synthesis, while melatonin treatments before ripening improve the final fruit quality.

Strigolactone Regulates Leaf Senescence in Concert with Ethylene in Arabidopsis.

Leaf senescence is not a passive degenerative process; it represents a process of nutrient relocation, in which materials are salvaged for growth at a later stage or to produce the next generation. Leaf senescence is regulated by various factors, such as darkness, stress, aging, and phytohormones. Strigolactone is a recently identified phytohormone, and it has multiple functions in plant development, including repression of branching. Although strigolactone is implicated in the regulation of leaf senescence, little is known about its molecular mechanism of action. In this study, strigolactone biosynthesis mutant strains of Arabidopsis (Arabidopsis thaliana) showed a delayed senescence phenotype during dark incubation. The strigolactone biosynthesis genes MORE AXIALLY GROWTH3 (MAX3) and MAX4 were drastically induced during dark incubation and treatment with the senescence-promoting phytohormone ethylene, suggesting that strigolactone is synthesized in the leaf during leaf senescence. This hypothesis was confirmed by a grafting experiment using max4 as the stock and Columbia-0 as the scion, in which the leaves from the Columbia-0 scion senesced earlier than max4 stock leaves. Dark incubation induced the synthesis of ethylene independent of strigolactone. Strigolactone biosynthesis mutants showed a delayed senescence phenotype during ethylene treatment in the light. Furthermore, leaf senescence was strongly accelerated by the application of strigolactone in the presence of ethylene and not by strigolactone alone. These observations suggest that strigolactone promotes leaf senescence by enhancing the action of ethylene. Thus, dark-induced senescence is regulated by a two-step mechanism: induction of ethylene synthesis and consequent induction of strigolactone synthesis in the leaf.

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.

Repressed ethylene production in the gynoecium of long-lasting flowers of the carnation 'White Candle': role of the gynoecium in carnation flower senescence.

Ethylene production and expression of ethylene biosynthetic genes was investigated in senescing flowers of carnation (Dianthus caryophyllus L.) cultivars 'White Candle (WC)' and 'Light Pink Barbara (LPB)', with long and short vase-lives, respectively. Ethylene production from the gynoecium and petals of senescing 'WC' flowers was below the limit of detection, in agreement with the repressed ethylene production from the whole flowers. However, exogenous ethylene treatment caused the accumulation of transcripts for DC-ACS1 and DC-ACO1 genes in both the gynoecium and petals, resulting in ethylene production from the flowers. Moreover, application of ABA or IAA, which are known to exhibit their action through the induction of ethylene synthesis in the gynoecium, to 'WC' flowers from their cut stem-end induced ethylene production and wilting in the flowers. These findings suggested that, in 'WC' flowers the mechanism of ethylene biosynthesis, i.e. the induction of expression of genes for ethylene biosynthesis and the action of resulting enzymes, was not defective, but that its function was repressed during natural senescence. Transcripts of DC-ACO1, DC-ACS3, and DC-ACS1 were present in the gynoecium of senescing 'LPB' flowers. In the gynoecium of senescing 'WC' flowers, however, the DC-ACO1 transcript was present, but the DC-ACS1 transcript was absent and the DC-ACS3 transcript was detected only in a small amount; the latter two were associated with the low rate of ethylene production in the gynoecium of 'WC' flowers. These findings indicated that the repressed ethylene production in 'WC' flowers during natural senescence is caused by the repressed ethylene production in the gynoecium, giving further support for the role of the gynoecium in regulating petal senescence in carnation flowers.

Characterization of Pear (Pyrus communis L.) Strains Unresponsive to Cold-induced Ripening in Relation to the Production and Action of Ethylene.

The process of cold-induced ripening of pear (Pyrus communis L.) fruits consists of four consecutive steps ; (1) perception of the cold stimulus and transduction of the signal, (2) induction of ethylene synthesis, (3) action of the produced ethylene, and (4) softening by the action of hydrolytic enzymes and related changes in fruit tissues. The two pear strains, P12-9 and P12-111, derived from the cross between 'La France' and 'Le Lectier' do not respond to cold-induced ripening. In this study, we characterized the possible points of metabolic block(s) in these pear strains to the cold-induced ripening in relation to the synthesis and action of ethylene. In P12-9 fruits, ACC synthase was induced and ACC content was increased by the cold treatment, resulting in ethylene production ; whereas exogenous ethylene did not induce softening of P12-9 fruits, suggesting that ethylene was not perceived. P12-111 fruits produced ethylene under some conditions, but did not when exposed to cold treatment. These fruits did not soften even after an abundance of ethylene was produced during a prolonged cold storage. These findings indicated that P12-111 fruits lack the ability to perceive the cold stimuli and to respond to ethylene. Whether the subsequent softening step in both of the strains is normal or not remains to be elucidated.

Enhanced ethylene production and peroxidase activity in IAA-overproducing transgenic tobacco plants is associated with increased lignin content and altered lignin composition

In a previous investigation, the lignin content of the xylem in the tobacco stem was shown to be greater in transgenic IAA-overproducing line C plants than in wild-type plants (Sitbon et al., Plant Physiol. 99 (1992) 1062–1069). Here, we confirm this observation and also show that the lignin composition in the transformants is altered, the ratio of syringyl to guaiacyl units being decreased due to an increase in guaiacyl units. Line C plants displayed an increased ethylene production in leaves and internodes, as well as a greater capacity to evolve ethylene in response to wounding and exogenous IAA. Line C plants also had greater peroxidase (POD) activity, whereas cinnamyl alcohol dehydrogenase and ß-glucosidase activities were similar in the two genotypes. The mRNA level of a tobacco anionic POD, previously associated with increased levels of lignin and related polyphenols when overexpressed in transgenic tobacco plants (Lagrimini, Plant Physiol. 96 (1991) 577–583), was increased in line C plants. It is suggested that the high IAA level in the transformants, through an induction of ethylene synthesis, increases POD activity and hence also lignin deposition.

Effect of picloram on resistant and susceptible yellow starthistle (Centaurea solstitialis): the role of ethylene

The noxious weed yellow starthistle is commonly controlled by the auxinic herbicide picloram. Induction of ethylene synthesis, epinasty, and reduction in shoot growth are typical symptoms of picloram treatment. Picloram did not induce ethylene evolution in the resistant accession RDW-1, though it caused a 250% increase in ethylene evolution in the susceptible wildtype SCI-1. The ethylene synthesis inhibitor aminoethoxyvinylglycine reduced the amount of ethylene induced by picloram in SCI-1 to control levels, but only reduced epinasty by 20% after 6 d. Aminoethoxyvinylglycine did not affect the reduction in shoot weight caused by picloram. The ethylene-releasing compound ethephon induced only a small amount of epinasty and had little effect on shoot weight in either accession. These results suggest that ethylene induced by picloram in wildrype plants plays only a minor role in the herbicidal effects of picloram. Furthermore, the resistance of the RDW-1 accession is not due to the lack of ethylene biosynthesis following picloram application to this accession.

Reduction in ethylene synthesis in parthenocarpic Actinidia deliciosa fruit induced by N-(2-chloro-4-pyridyl)-N′-phenylurea

Parthenocarpic kiwifruit Actinidia deliciosa was produced and induction of ethylene synthesis in response to ethylene treatment studied. At anthesis, flowers were treated with N -(2-chloro-4-pyridyl)- N ′-phenylurea (CPPU). CPPU-treated parthenocarpic fruit and pollinated normal fruit were harvested in early November, and then treated with 1000 μ l l −1 ethylene at 20°C for 24 h. Ethylene production following ethylene treatment was reduced and delayed in the parthenocarpic fruit. To investigate the mechanism of this reduction in ethylene synthesis, 1-aminocyclopropane-1-carboxylic acid (ACC) concentrations, and gene expression of ACC synthase (using a cDNA probe, AD-ACS1) and of ACC oxidase (with a cDNA probe, AD-ACO1) were analyzed. ACC concentrations and levels in ACC synthase transcripts increased in the pollinated fruit 2 days after the 24 h ethylene treatment, but not in the parthenocarpic fruit. Accumulation of ACC oxidase transcripts was stimulated immediately by the 24 h ethylene treatment in both pollinated and parthenocarpic fruit. These results suggest that suppression of ethylene synthesis in parthenocarpic fruit resulted mainly from suppressed expression of ACC synthase.

Products Released from Enzymically Active Cell Wall Stimulate Ethylene Production and Ripening in Preclimacteric Tomato (Lycopersicon esculentum Mill.) Fruit

Enzymically active cell wall from ripe tomato (Lycopersicon esculentum Mill.) fruit pericarp release uronic acids through the action of wall-bound polygalacturonase. The potential involvement of products of wall hydrolysis in the induction of ethylene synthesis during tomato ripening was investigated by vacuum infiltrating preclimacteric (green) fruit with solutions containing pectin fragments enzymically released from cell wall from ripe fruit. Ripening initiation was accelerated in pectin-infiltrated fruit compared to control (buffer-infiltrated) fruit as measured by initiation of climacteric CO(2) and ethylene production and appearance of red color. The response to infiltration was maximum at a concentration of 25 micrograms pectin per fruit; higher concentrations (up to 125 micrograms per fruit) had no additional effect. When products released from isolated cell wall from ripe pericarp were separated on Bio-Gel P-2 and specific size classes infiltrated into preclimacteric fruit, ripening-promotive activity was found only in the larger (degree of polymerization >8) fragments. Products released from pectin derived from preclimacteric pericarp upon treatment with polygalacturonase from ripe pericarp did not stimulate ripening when infiltrated into preclimacteric fruit.

Changes during low‐oxygen storage in the effects of ethylene on induction of ethylene synthesis and stimulation of respiration of ‘Gloster 69’ apples

The ability of ethylene to stimulate respiration and advance the onset of rapid ethylene production was investigated at different times during storage of ‘Gloster 69’ apples in 2 kPa O2 at 1.5–3.5°C. Ethylene stimulated respiration in apples at 15°C immediately after harvest; maximal rates were recorded at 10–1000 μl I−1 but attainment of these rates was delayed after low O2 storage until day 3 of treatment at 15°C. The onset of rapid ethylene production at 15°C occurred later in non‐ethylene‐treated apples after storage than after harvest. Ethylene production was induced in some apples during ethylene treatment for 3 or 6 days; in others it was induced about 20 days after treatment, but a proportion of the fruit showed no induction in the 45‐day duration of experiments. An ethylene treatment at 10 μl I−1 led to a near maximal increase in the frequency of induction of ethylene production at all times. After storage apples were mainly induced during treatment or not induced, whereas after harvest induction after treatment was more frequent. The presence of 2000 μl l−1 norbornadiene during ethylene treatment inhibited the stimulation of respiration and the induction of ethylene production; this inhibition was only partly reversed by ethylene at 1000 μl l−1 the experiments suggest that receptors for ethylene were present at all stages but that response capacity changed during storage.

Stress-induced Ethylene Production in the Ethylene-requiring Tomato Mutant Diageotropica

Ethylene synthesis in vegetative tissues is thought to be controlled by indoleacetic acid (IAA). However, ethylene synthesis in the diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) was much less sensitive to IAA than in the normal variety (VFN8). Yet, mechanical wounding stimulated ethylene production by the mutant. The dgt tomato provides an opportunity to study the regulation of stress ethylene independent of IAA effects. Waterlogging (i.e. anaerobic stress) stimulated production of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), in the roots. The ACC was transported to the shoot where it was converted to ethylene. The dgt mutant efficiently utilized ACC for ethylene synthesis under aerobic conditions. The results confirm that the genetic lesion in dgt is located at a step prior to the formation of ACC. Furthermore, induction of ethylene synthesis by anaerobic or mechanical stresses in this mutant is independent of IAA action.