Reduced Ethylene Synthesis Research Articles

Biostimulant-induced mitigation of cold and drought stresses in zucchini plants

Currently, water and cold stresses are among the primary adverse factors affecting global crop production. Biostimulants are increasingly recognized as valuable tools for enhancing plant tolerance to abiotic stresses. F4.3S is a novel biostimulant that contains compounds such as allantoin, ascorbate, salicylic acid, amino acids such as glutamate, proline, and glycine, and sources of selenium, molybdenum, and cobalt. The objective of this study was to assess the tolerance of zucchini cv. Dynaic plants supplied with F4.3S to water and cold stresses and to identify the potential action mechanisms. For this purpose, an experiment was set up in pots with plants to which the biostimulant was applied before and after subjecting the plants to stress conditions, and parameters of biomass, stress, photosynthesis, and ethylene response were evaluated. The results showed that plants supplied with F4.3S presented a better tolerance to both stresses, which was reflected in higher biomass. The potential action mechanisms could be the stimulation of photosynthetic efficiency, preventing excessive stomatal closure, maintaining a high rate of net photosynthesis, and reducing reactive oxygen species generation. Additionally, increased accumulation of protective anti-stress compounds such as proline and carotenoids, along with reduced ethylene synthesis, likely contributed to the plants' enhanced recovery post-stress. In conclusion, the F4.3S biostimulant emerges as a promising agent for augmenting plant tolerance to abiotic stresses, which is crucial for sustainable agricultural practices.

Post-harvest management and characteristics of melon cultivars fruits and their prospects in the Roraima savannah: a review

The melon (Cucumis melo L.) holds significant economic importance on the global stage, with Brazil standing out as a strong exporter. Climatic conditions such as high temperatures, low relative humidity, and extended periods of sunlight are beneficial for the fruit's production and quality. The Northeast region of Roraima, particularly the municipalities of Bonfim and Normandia, close to the border with Guyana, has a semi-arid climate with an average annual rainfall between 1,200 and 1,400 mm. After harvesting, horticultural products begin to respire, a process that compromises post-harvest quality, leading to a decrease in organoleptic characteristics, firmness, sugar content, and loss of mass. The Cantaloupensis and Reticulatus melons, which are climacteric, have a high synthesis of ethylene and high respiratory rates in the fruit, resulting in flavor deterioration, firmness loss, and a shorter post-harvest shelf life. In contrast, non-climacteric melons, such as the inodorus group, display reduced ethylene synthesis, white flesh, subtle aroma, no pronounced ripening, and a longer post-harvest lifespan. It's worth noting that the melon market offers a variety of significant cultivars, resistant to pests, with high productivity and excellent post-harvest quality. This study aimed to address a literature review on the management of melon cultivation, development conditions of the crop, and post-harvest of melon cultivars in the Roraima Savanna."

Aminoethoxyvinylglycine Reduces Preharvest Fruit Drop and Fruit Ethylene Evolution in ‘Red Delicious’ Apple but Affects Fruit Size and Quality Inconsistently

Aminoethoxyvinylglycine (AVG) is widely used in commercial apple (Malus ×domestica Borkh.) production to reduce preharvest fruit drop (PFD) and delay ripening for harvest management. Recently, the maximum allowable concentration of AVG was doubled (up to 264 mg⋅L−1). Reports of the relationship between the AVG concentration and fruit growth, size, and quality have been contradictory. We evaluated the relationship between the AVG concentration and PFD, fruit size, fruit quality, and expression of ethylene signaling-related and cell wall modification-related genes. Experiments were conducted in 2019 and 2020 using mature ‘Red Delicious’ in western North Carolina. The AVG treatments [0 and 132 (AVG-1x) and 264 mg⋅L−1 (AVG-2x)] were applied 3 weeks before the expected harvest. The AVG treatments reduced fruit drop and internal ethylene concentration relative to the control in both years. There was no difference in drop between AVG-1x and AVG-2x applications. Only in 2020 did AVG treatments delay fruit softening and starch hydrolysis and reduce soluble solids concentration. There were no effects on red fruit color development. Fruit size was unaffected by AVG in 2019, but it was reduced in 2020 with the AVG-2x application. AVG reduced ethylene synthesis and altered signaling, evidenced by decreased relative expression of genes related to ethylene signaling (ARGOS1, ARGOS2). AVG applications also reduced the expression of EXPA8;1, suggesting that reduced cell wall disassembly was associated with a reduction in fruit softening. These results indicate that preharvest applications of 132 mg⋅L−1 AVG effectively reduced PFD via altering ethylene evolution and signaling. Use of a higher AVG concentration was of limited benefit.

Reduced ethylene synthesis of mangoes under high CO2 atmosphere storage

. High CO2 atmospheres have been reported to be accountable for slower ripening processes of many fruit species. In modified or controlled atmosphere storage of mangoes (Mangifera indica L.) delayed ripening is attributed to the effects of CO2 on ethylene biosynthesis, which is reduced under CO2 concentrations beyond 10%. In the present work the objective was to determine if those elevated CO2 atmospheres on ethylene synthesis could be attributed to the action of CO2 upon ACC oxidase. Mature green or tree ripe `Tommy Atkins` mangoes were, in four experiments, held in a flow through system of either 10 or 25% CO2 mixed to 5% O2 or only air for 14 or 21 days at 5, 8 or 12°C. Mangoes in the 25% CO2 atmosphere did not produce detectable levels of ethylene, whereas under 10% CO2 the production rates were significantly suppressed at 5 or 8°C. However, 1-aminocyclopropane-1-carboxylic acid (ACC) concentrations in mango mesocarp tissue at retrieval from storage were similar to the air controls and ACC synthase activity was not completely inhibited. The direct effects of CO2 concentrations on ACC oxidase activity is to be considered the most important factor in inhibiting ethylene biosynthesis of mangoes under 25% CO2 atmospheres.

Application of rice endophytic Bradyrhizobium strain SUTN9-2 containing modified ACC deaminase to rice cultivation under water deficit conditions

ABSTRACT Bacterial 1-aminocyclopropane-1-carboxylate (ACC) deaminase is a key factor for alleviating the plant ethylene biosynthesis, which is induced by stress. The ACC deaminase-improved strains of the rice endophytic Bradyrhizobium sp. SUTN9-2, SUTN9-2 (ACCDadap) and SUTN9-2:pMG103::acdRS, exhibit 1.4- and 8.9-fold higher ACC deaminase activity than the wild type, respectively (Sarapat S, Songwattana P, Longtonglang A, Umnajkitikorn K, Girdthai T, Tittabutr P, Boonkerd N, Teaumroong N. 2020. Effects of Increased 1-Aminocyclopropane-1-Carboxylate (ACC) Deaminase Activity in Bradyrhizobium sp. SUTN9-2 on Mung Bean Symbiosis under Water Deficit Conditions. Microbes Environ. 35). The effects of these on rice growth under water deficit conditions were evaluated. The bacterial inoculations reduced ethylene synthesis, leading to a reduction in membrane destruction and the chlorophyll content of rice. Furthermore, the bacterial inoculations improved the leaf relative water content, survival, recovery rates, and improved the crop yield in field conditions. Therefore, the water deficit tolerance of rice was improved by controlling ethylene biosynthesis by improving ACC deaminase activity with endophytic SUTN9-2. Moreover, the SUTN9-2 (ACCDadap) strain can be used as a bio-inoculant under field conditions to enhance rice growth, grain yield, and enhance drought tolerance.

Quinclorac resistance in Echinochloa phyllopogon is associated with reduced ethylene synthesis rather than enhanced cyanide detoxification by β-cyanoalanine synthase.

Multiple herbicide resistant Echinochloa phyllopogon exhibits resistance to the auxin herbicide quinclorac. Previous research observed enhanced activity of the cyanide-detoxifying enzyme β-cyanoalanine synthase (β-CAS) and reduced ethylene production in the resistant line, suggesting β-CAS-mediated cyanide detoxification and insensitivity to quinclorac stimulation as the resistance mechanisms. To investigate the molecular mechanisms of quinclorac resistance, we characterized the β-CAS genes alongside plant transformation studies. The association of β-CAS activity and ethylene production to quinclorac resistance was assayed in the F6 progeny of susceptible and resistant lines of E. phyllopogon. A single nucleotide polymorphism in a β-CAS1 intron deleted aberrantly spliced mRNAs and enhanced β-CAS activity in the resistant line. The enhanced activity, however, was not associated with quinclorac resistance in F6 lines. The results were supported by lack of quinclorac resistance in Arabidopsis thaliana expressing E. phyllopogon β-CAS1 and no difference in quinclorac sensitivity between β-CAS knockout and wild-type rice. Reduced ethylene production co-segregated with quinclorac resistance in F6 lines which were previously characterized to be resistant to other herbicides by an enhanced metabolism. β-CAS does not participate in quinclorac sensitivity in E. phyllopogon. Our results suggest that a mechanism(s) leading to reduced ethylene production is behind the resistance. © 2019 Society of Chemical Industry.

AMINOETHOXYVINYLGLYCINE AND FOLIAR ZINC TREATMENTS PLAY A KEY ROLE IN PRE-HARVEST DROPS AND FRUIT QUALITY ATTRIBUTES OF ‘WILLIAM’S PRIDE’ APPLE

Effects of pre-harvest aminoethoxyvinylglycine (AVG, 250 mg L–1) and zinc (0.3% ZnSO4) treatments on pre-harvest fruit drops, internal ethylene concentration (IEC), flesh firmness, color characteristics (L*, chroma and hue angle), soluble solids content (SSC), acidity, total phenolics, antioxidant activity, flesh and leaf micronutrients and macronutrients of ‘William’s Pride’ apples, were investigated in this study. AVG was sprayed 4 weeks before the anticipated harvest date and Zn was sprayed when the fruits reached the size of a walnut. As compared to the control, both the single AVG and zinc treatments significantly reduced the pre-harvest drops. However, combined AVG + Zinc treatments were found to be more effective in reducing the pre-harvest drops. At the last measurement date (15th of August), 60% fruit drop was measured in control, but 22% in AVG + Zinc treatment. AVG and AVG + Zinc treatments reduced ethylene synthesis. On the other hand, single zinc treatments stimulated ethylene synthesis. AVG treatments retarded red skin color development, but zinc treatments again stimulated red color development. As compared to the control and single zinc treatments, AVG-treated fruits had greater firmness and acidity values, but lower SSC values. While AVG treatments increased the total phenolics and antioxidant activity, zinc treatments decreased these attributes. As compared to the control, zinc treatments significantly increased flesh Cu, N, P and K contents and leaf Mn, N and P contents. Based on present findings, it was concluded that AVG could be used as an efficient tool to reduce the pre-harvest drops in apples.

Inhibition of Ethylene Biosynthesis and Associated Gene Expression by Aminoethoxyvinylglycine and 1-Methylcyclopropene and Their Consequences on Eating Quality and Internal Browning of ‘Starkrimson’ Pears

‘Starkrimson’ is a highly profitable red-skinned european pear (Pyrus communis) cultivar that has a short storage life due mainly to the development of a mealy texture upon ripening and an internal browning (IB) disorder during or after storage. In 2013, ‘Starkrimson’ pears were sprayed with aminoethoxyvinylglycine (AVG) at 0, 30, 60, and 120 mg·L−1 1 week before harvest or treated with 1-methylcyclopropene (1-MCP) at 0.3 µL·L−1 for 24 hours shortly after harvest, then stored at −1.1 °C and evaluated over a 16-week period. The experiment was repeated in 2014. After 2 weeks of storage, control fruit (nontreated) had a higher respiration rate and ethylene biosynthesis than AVG or 1-MCP-treated fruit. Following 12 weeks of storage, control fruit exhibited a greater incidence of mealy texture and greater extractable juice (EJ) after ripening, and by 16 weeks significantly higher IB relative to AVG and 1-MCP-treated fruit. AVG at 30 mg·L−1 had little effect on any of the storage responses measured compared with control. AVG at 60 mg·L−1 reduced ethylene synthesis, respiration rate, and titratable acidity (TA) loss and maintained high eating quality with low EJ. Fruit treated with 60 mg·L−1 AVG also developed markedly less IB following 16 weeks of storage than control or 30 mg·L−1 AVG treatments. AVG at 120 mg·L−1 did not improve storage quality achieved with 60 mg·L−1 but delayed ripening capacity by 1 month. 1-MCP markedly inhibited ethylene synthesis and respiration rate and eliminated IB during 16 weeks of storage; however, 1-MCP-treated fruit required 14 days at 20 °C to ripen to high eating quality following 12 to 16 weeks of storage compared with 5 days for 60 mg−L−1 AVG. Both AVG and 1-MCP suppressed the expressions of ethylene synthesis (PcACS1, PcACS4, PcACS5, and PcACO1) and perception genes (PcETR1, PcETR2, and PcETR5) although 1-MCP was more efficient than AVG. In conclusion, preharvest AVG applications at 60 mg·L−1 or postharvest 1-MCP treatment at 0.3 µL·L−1 extended storage life of ‘Starkrimson’; however, 1-MCP inhibited ripening capacity whereas 60 mg·L−1 AVG did not.

Pré-resfriamento sobre a qualidade de pêssegos 'Chiripá'

O objetivo deste trabalho foi avaliar a qualidade física e química e a incidência de distúrbios fisiológicos em pêssegos 'Chiripá' submetidos a diferentes formas de pré-resfriamento. Os tratamentos avaliados foram: [1] resfriamento convencional em câmara frigorífica (-0,5°C e UR de 95%); [2] resfriamento sob ar forçado (-1,5°C) até a temperatura da polpa atingir 0°C; [3] resfriamento em água a 1°C (RA) até 15°C; [4] RA até 10°C; [5] RA até 5°C; [6] RA até 1°C. Os frutos foram analisados após 35 dias a -0,5°C, mais dois e quatro dias a 20°C. Verificou-se menor síntese de etileno nos frutos submetidos ao resfriamento lento e ao resfriamento com ar forçado, durante o período a 20°C. Nesses frutos, a quantidade de suco livre foi significativamente menor após quatro dias a 20°C, demonstrando uma aparente relação entre a reduzida síntese de etileno e a baixa suculência, o que é uma manifestação de lanosidade. Os frutos resfriados de forma lenta apresentaram firmeza da polpa mais elevada. Todas as formas de resfriamento com a água na temperatura de 1°C resultaram em maior porcentagem de frutos com manchas na epiderme, possivelmente em razão da baixa temperatura da água do pré-resfriador, indicando que o resfriamento em água não é recomendado para pêssegos 'Chiripá'.

Tomato Transcriptional Changes in Response toClavibacter michiganensissubsp.michiganensisReveal a Role for Ethylene in Disease Development

Clavibacter michiganensis subsp. michiganensis (Cmm) is a gram-positive actinomycete, causing bacterial wilt and canker disease in tomato (Solanum lycopersicum). Host responses to gram-positive bacteria and molecular mechanisms associated with the development of disease symptoms caused by Cmm in tomato are largely unexplored. To investigate plant responses activated during this compatible interaction, we used microarray analysis to monitor changes in host gene expression during disease development. This analysis was performed at 4 d postinoculation, when bacteria were actively multiplying and no wilt symptoms were yet visible; and at 8 d postinoculation, when bacterial growth approached saturation and typical wilt symptoms were observed. Of the 9,254 tomato genes represented on the array, 122 were differentially expressed in Cmm-infected plants, compared with mock-inoculated plants. Functional classification of Cmm-responsive genes revealed that Cmm activated typical basal defense responses in the host, including induction of defense-related genes, production and scavenging of free oxygen radicals, enhanced protein turnover, and hormone synthesis. Cmm infection also induced a subset of host genes involved in ethylene biosynthesis and response. After inoculation with Cmm, Never ripe (Nr) mutant plants, impaired in ethylene perception, and transgenic plants with reduced ethylene synthesis showed significant delay in the appearance of wilt symptoms, compared with wild-type plants. The retarded wilting in Nr plants was a specific effect of ethylene insensitivity, and was not due to altered expression of defense-related genes, reduced bacterial populations, or decreased ethylene synthesis. Taken together, our results indicate that host-derived ethylene plays an important role in regulation of the tomato susceptible response to Cmm.

Reduced symptoms of Verticillium wilt in transgenic tomato expressing a bacterial ACC deaminase

Summary Ethylene evolved during compatible or susceptible disease interactions may hasten and/or worsen disease symptom development; if so, the prevention of disease-response ethylene should reduce disease symptoms. We have examined the effects of reduced ethylene synthesis on Verticillium wilt (causal organism, Verticillium dahliae) of tomato by transforming tomato with ACC deaminase, which cleaves ACC, the immediate biosynthetic precursor of ethylene in plants. Three promoters were used to express ACC deaminase in the plant: (i) CaMV 35S (constitutive expression); (ii) rolD (limits expression specifically to the site of Verticillium infection, i.e. the roots); and (iii) prb-1b (limits expression to certain environmental cues, e.g. disease infection). Significant reductions in the symptoms of Verticillium wilt were obtained for rolD- and prb-1b-, but not for 35S-transformants. The pathogen was detected in stem sections of plants with reduced symptoms, suggesting that reduced ethylene synthesis results in increased disease tolerance. The effective control of formerly recalcitrant diseases such as Verticillium wilt may thus be obtained by preventing disease-related ethylene production via the tissue-specific expression of ACC deaminase.

658 Engineering Ethylene Synthesis and Perception for Fun and Profit

Ethylene-based technologies for controlling ripening in climacteric fruit have been in widespread use for a number of years. Likewise, using chemicals that block ethylene synthesis or perception have been widely used to extend shelf life of a variety of horticultural commodities. In the last few years, our understanding of the molecular mechanisms for ethylene synthesis and perception has greatly expanded. Genes encoding the ethylene biosynthetic enzymes and the ethylene receptor have been cloned from many plant species, which has meant that molecular approaches to engineering reduced ethylene synthesis or perception are now reality. Scientists have been examining the feasibility of using molecular approaches to control ethylene in a variety of horticultural and ornamental species. They have shown that it is relatively easy to produce plants that are reduced in either synthesis or response to ethylene. However, scientists have uncovered some issues associated with commercial-level use of these transgenic plants. Overall, my results illustrate the great potential of the technology to control the rate of climacteric fruit ripening, abscission, and ethylene-induced senescence in multiple species, but using transgenes in many cases needs to be directed to target tissues through the use of tissue-specific transcriptional promoters. With that caveat in mind, there should be a strong future for improving the quality of a range of agronomic and horticultural species.

Nucleotide Sequence of a cDNA Clone Encoding 1-Aminocyclopropane-1-Carboxylic Acid Synthase from Broccoli

Ethylene regulates many processes in plant growth, development, and senescence. Two enzymes, ACC synthase and ACC oxidase, are responsible for ethylene biosynthesis from its precursor S-adenosyl Met (Yang and Hoffman, 1984), and blocking the synthesis of these enzymes in antisense RNA experiments results in reduced ethylene synthesis (Hamilton et al., 1990; Oeller et al., 1991). Functional identification of cDNA clones encoding ACC synthase has been achieved by expression studies in Escherichia coli and yeast and by sequence comparisons to peptides purified from ACC synthase protein (Sato and Theologis, 1989; Yip et al., 1990; Dong et al., 1991). Broccoli florets are composed of both vegetative and floral tissues that senesce rapidly after harvest. The most visible change is Chl degradation in the sepals, which begins within 48 h of harvest (tissues held in darkness at ZO'C), and is associated with increases in ACC oxidase mRNA and ethylene synthesis from within the florets (Tian et al., 1994; B. J. Pogson, unpublished data). We report the sequence of a cDNA clone (pbroc3, Table I) isolated from a cDNA library in AZapII (Stratagene) constructed from poly(A+) A from broccoli florets held at 2OoC in darkness for 48 h after harvest. The cDNA is 1734 bp long and encodes an open reading frame of 481 amino acids. The nucleotide and predicted amino acid sequences show high identity with ACC synthase from tomato (LEACC2G) and apple (pAASZ), respectively (Dong et al., 1991; Rottmann et al., 1991). T h e predicted peptides of the broccoli, tomato, and apple clones were aligned (Devereux et al., 1984), and regions of high identity were found to correspond to conserved regions of other ACC synthases (Park et al., 1992). The pbroc3 cDNA contained a region with 83% amino acid identity (100% similarity based on conservative changes) with the peptide sequence identified as the active site of ACC synthase (Yip et al., 1990).

Reduced ethylene synthesis by transgenic tomatoes expressing S-adenosylmethionine hydrolase

We have utilized a gene from bacteriophage T3 that encodes the enzyme S-adenosylmethionine hydrolase (SAMase) to generate transgenic tomato plants that produce fruit with a reduced capacity to synthesize ethylene. S-adenosylmethionine (SAM) is the metabolic precursor of 1-aminocyclopropane-1-carboxylic acid, the proximal precursor to ethylene. SAMase catalyzes the conversion of SAM to methylthioadenosine and homoserine. To restrict the presence of SAMase to ripening fruit, the promoter from the tomato E8 gene was used to regulate SAMase gene expression. Transgenic tomato plants containing the 1.1 kb E8 promoter bore fruit that expressed SAMase during the breaker and orange stage of fruit ripening and stopped expression after the fruit fully ripened. Plants containing the 2.3 kb E8 promoter expressed SAMase at higher levels during the post-breaker phases of fruit ripening and had a substantially reduced capacity to synthesize ethylene.

Roles of Ethylene in the Development of Superficial Scald in `Cortland' Apples

Ethephon and diphenylamine (DPA) were used to examine the role of ethylene production in biochemical changes that precede development of superficial scald on `Cortland' apples (Malus domestica Borkh.) after cold storage. Treatments modified α-farnesene and conjugated triene (CT) accumulations in fruit peel, and their effects on CTs differed depending on whether CTs were measured at 258 nm (CT258) or 281 nm (CT281). Ethephon induced rapid and delayed effects on fruit, the former being stimulation of ethylene production and α-farnesene and CT accumulation in fruit peel, which could increase scald development, and the latter being a disproportionately higher accumulation of CT258 than of CT281 during prolonged cold storage, which was associated with reduced scald development. DPA treatment at harvest also produced rapid and delayed effects. It immediately reduced ethylene synthesis and α-farnesene and CT accumulation. In addition, during fruit storage at 0C, DPA reduced accumulation of CT281 more than that of CT258. The rapid and delayed effects of DPA should contribute to less scald development. These results showed that ethylene probably was involved in effects of ethephon and DPA on scald development and suggest that ethylene has a fundamental role in changes associated with superficial scald development.

Ripening Physiology of Fruit from Transgenic Tomato (Lycopersicon esculentum) Plants with Reduced Ethylene Synthesis.

The physiological effects of reduced ethylene synthesis in a transgenic tomato (Lycopersicon esculentum) line expressing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase enzyme have been examined. Fruit from the transgenic line 5673 ripen significantly slower than control fruit when removed from the vine early in ripening. In contrast, fruit that remain attached to the plants ripen much more rapidly, exhibiting little delay relative to the control. Ethylene determinations on attached fruit revealed that there was significantly more internal ethylene in attached than detached fruit. The higher ethylene content can fully account for the observed faster on-the-vine ripening. All of the data are consistent with a catalytic role for ethylene in promoting many, although not all, aspects of fruit ripening. Biochemical analyses of transgenic fruit indicated no significant differences from controls in the levels of ACC oxidase or polygalacturonase. Because transgenic fruit are significantly firmer than controls, this last result indicates that other enzymes may have a significant role in fruit softening.

Reduced ethylene synthesis in EFE antisense tomatoes has differential effects on fruit ripening processes

Abstract Modified tomato plants ( Lycopersicon esculentum Mill. cv. Ailsa Craig) which express antisense RNA to the ethylene-forming enzyme (EFE) show greatly reduced ethylene synthesis (Hamilton et al., 1990). We have now examined the ripening characteristics of fruit from homozygous antisense and control plants. Although the interval between anthesis and colour change was not altered, thereafter pigment formation was retarded, and in addition, the rate of loss of acidity was reduced. However, the softening rate was not inhibited during ripening, but was retarded in the over-ripening phase. Exogenous ethylene enhanced the colouration rate in antisense fruit more than that for control samples, but had little effect on the softening rate. These results imply that the level of ethylene production has differential effects on the various ripening processes. The antisense fruit were less susceptible to damage during ripening and harvest, and survived in good condition for longer storage periods. However, the antisense tomatoes softened more rapidly when harvested and stored at a constant 20°C than when ripened on the plant in the glasshouse.

Effects of Waxing on Moisture Loss and Ripening of ‘Fuerte’ Avocado Fruit

Abstract Internal atmosphere composition, respiration rate, ethylene production, weight loss, and firmness were monitored during the ripening of waxed and nonwaxed avocado fruit (Persea americana Mill.) during storage at 5°C, and ripening at 20°. Artificial waxing, which usually forms a uniform film over the closely packed platelet structure of the natural wax, was sometimes incomplete. Waxing caused a slight buildup of CO2 and possible reduction in internal O2 concentrations during the preclimacteric of stored fruit, and may have reduced ethylene synthesis during the climacteric. Waxing caused a 1-day delay in fruit softening under extended cold-storage conditions.

Silver Ion Inhibits Ethylene Synthesis and Action in Ripening Fruits1

Abstract Ag(I), applied in aqueous solution as AgNO3, inhibited ethylene synthesis and ripening of mature green banana fruit slices and pericarp discs of mature green tomato fruit. It also inhibited ethylene production by cortical tissue from post-climacteric apples. Concentrations of Ag(I) which reduced ethylene synthesis had an inconsistent effect on CO2 production: no effect on banana slices (1.0 mm Ag+), stimulation in apple tissue (0.1 mm Ag+), and inhibition in tomato tissue (0.3 mm Ag+). This was accompanied by a slight amount of tissue necrosis at these concentrations. Of the 7 metallic salts tested, only Ag(I) inhibited ripening and ethylene synthesis at observed non-phytotoxic levels. Inhibition of ripening and ethylene synthesis by Ag(I) was evident in tissue treated with sufficient exogenous ethylene to elicit both responses in control tissue. The inability of applied ethylene to overcome the inhibitory effect of Ag(I) suggests that the silver ion may interfere with the primary action of ethylene in the tissue.