Ethylene Biosynthesis in Fruit Tissues

Wound-induced ethylene synthesis by subapical stem sections of etiolated Pisum saivum L., cv. Alaska seedlngs, as described by Saltveit and Dilley (Plant Physiol 1978 61: 447450), was half-saturated at 3.6% (v/v) 02 and saturated at about 10% 02. Corresponding values for CO2 production during the same period were 1.1% and 10% 02, respectively. Anaerobiosis stopped all ethylene evolution and delayed the characteristic pattern of wound ethylene synthesis. Exposing tissue to 3.5% CO2 in air in a flowthrough system reduced wound ethylene synthesis by 30%. Enhancing gas diffusivity by reducing the total pressure to 130 mm Hg almost doubled the rate of wound ethylene synthesis and this effect was negated by exposure to 250 #1 liter-1 propylene. Applied ethylene or propylene stopped wound ethylene synthesis during the period of application, but unlike N2, no lag period was observed upon flushing with air. It is concluded that the characteristic pattern of wound-induced ethylene synthesis resulted from negative feedback control by endogenous ethylene.No wound ethylene was produced for 2 hours after excision at 10 or 38 C. Low temperatures prolonged the lag period, but did not prevent induction of the wound response, since tissue held for 2 hours at 10 C produced wound ethylene immediately when warmed to 30 C. In contrast, temperatures above 36 C prevented induction of wound ethylene synthesis, since tissue cooled to 30 C after 1 hour at 40 C required 2 hours before ethylene production returned to normal levels. The activation energy between 15 and 36 C was 12.1 mole kilocalories degree-'.A rapidly induced, transitory increase in the rate of ethylene synthesis has been observed in a variety of excised tissues (1,24). The wound response was recently characterized in Pisum sativum L., cv. Alaska (24). In subapical stem tissue wound-induced ethylene production at 25 C increased linearly after a lag period of 26 min from 2.7 nl g-' hr-' to the first maximum of 11.3 nl g-' hr-' at 56 min. The rate of production then decreased to a minimum at 90 min, increased to a lower second maximum at 131 min, and then declined over a period of about 100 min to about 4 nl g-' hr-'. The magnitude of the response varied slightly from experiment to experiment, but the time sequence was constant for tissue excised from a given region of the pea seedling. In this study we examined the 02 and temperature dependency of woundinduced ethylene synthesis by etiolated 'Alaska' pea stem sections.Vegetative, ripening, and senescent tissue require 02 for ethylene synthesis (1,3, 6,13,21,29

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confidence: 56%

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confidence: 99%

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Rapidly Induced Wound Ethylene from Excised Segments of Etiolated Pisum sativum L., cv. Alaska

Saltveit¹,

Dilley²

1978

“…Subsequently, albedo has been used for studying the mode of ethylene production in the Satsuma mandarin. Methionine has been shown to be a precursor of ethylene in plants (2,7). In the present experiments L-[I4C]methionine was used to test the efficiency of methionine as a possible precursor of ethylene in the albedo tissue.…”

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confidence: 99%

Ethylene Production by Albedo Tissue of Satsuma Mandarin (Citrus unshiu Marc.) Fruit

Hyodo

1977

Isolated albedo tissue of Satsuma mandarin (Citrus unshiu Marcovitch, cv. Owari) fruit produced a large quantity of ethylene during incubation at 26 C in the dark. When sliced, albedo tissue began producing ethylene at an increasing rate until a maximum was reached after incubation for about 30 hours. Aged albedo discs which were capable of producing ethylene, actively converted L-IU-14CJmethionine into both ethylene and carbon dioxide. In fresh tissue, almost no measurable conversion of radioactive methionine into ethylene took place. Conversion of labeled L-methionine into ethylene was totally inhibited by the addition of nonradioactive L-methionine or L-ethionine. It appears possible, from these finding, that methionine is a precursor of ethylene in the aged albedo discs. Ethylene synthesis in the aged albedo tissnue was markedly reduced in the presence of cycloheximide, suggesting that there may be a rapid turnover of the ethylene-producing system, and that its formation involves protein synthesis. Actinomycin D exerted no effect.It has been demonstrated by Aharoni (1) that young, unripe oranges evolve a large amount of ethylene after harvest, paralleling a marked increase in respiration. Similar findings have been made by Eaks (3) for young fruits of grapefruit and oranges. Recently, I have also reported that young, immature fruit of Satsuma mandarin produced a great amount of ethylene after harvest (5). The rate of ethylene production by Satsuma mandarin fruit markedly decreased as the fruit developed and increased in weight. When young fruits were cut into small pieces (e.g. quarters or eighths) ethylene was produced at a much greater rate than by the intact fruit (5). Similar results were obtained with isolated albedo tissue. Albedo discs vigorously evolved ethylene, even though the tissue was taken from fruit which did not produce ethylene when intact. Subsequently, albedo has been used for studying the mode of ethylene production in the Satsuma mandarin. Methionine has been shown to be a precursor of ethylene in plants (2,7). In the present experiments L-[I4C]methionine was used to test the efficiency of methionine as a possible precursor of ethylene in the albedo tissue. MATERIALS AND METHODSSatsuma mandarin fruit (Citrus unshiu Marcovitch, cv. Owari) were harvested from the orchard during the months from July to November 1975. Ethylene production, respiration, increase in fresh weight, and some properties of the postharvest fruit were described elsewhere (5). Discs of the peel of the fruit were excised with a cork borer 9 mm in diameter. Albedo discs (2-4 mm thick), separated from the flavedo, were placed in a 130-ml Erlenmeyer flask and the flask was sealed with a rubber serum cap. Discs were incubated in the dark at 26 C. After closure for 1 hr, the atmosphere in the flasks was sampled through the serum caps at regular intervals with a plastic syringe, and ethylene concentration was determined. After each sampling, the flasks were flushed with air and then resealed. Ethylene was measured o...

“…This was verified in banana (5), tomato (9), and avocado (3) fruits. Baur et al (3) demonstrated that the levels of applied, labeled methionine in avocado fruits dropped 60% during the respiratory climacteric rise. Similar results were reported by Yu et al (18) with endogenous free methionine in tomato fruits.…”

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confidence: 99%

Free Methionine Levels in rin and Normal Isogenic Tomato Fruits Ripened in the Field or in Storage

Gonzalez¹,

Brecht²,

Rehkugler³

1976

Free methionine levels in rin and normal tomato fruits were determined microbiologically. Similar levels (1750 ,ug/100 g fresh weight) for mature green fruits of both rin and a normal isogenic line suggest that the lack of ripening of rin fruits is not due to low methionine levels. Methionine levels of mature green rin and normal fruits were 1750 ,lg/ 100 g fresh weight. Normal fruits ripened either on or off the vine were 2860 and 2500 ug/100 g fresh weight, respectively. The rin fruits which were left on the plant or held in air at 20 C until soft and yellow were significantly lower in methionine than C2H4-treated rin fruits or any normal fruits. Harvested rin and normal fruits held at 20 C in continuously applied ethylene (10 jdl/1) had higher methionine levels than comparable air controls; levels in treated rin fruits were significantly higher than those in normal fruits.Although several substances have been proposed as precursors to ethylene in higher plants (7. 13, 15, 16), present evidence favors the hypothesis that methionine is the primary precursor of ethylene (17). Using "4C-labeled methionine on various positions, Lieberman et al. (8) showed that ethylene was derived from carbons 3 and 4 of methionine in apples. This was verified in banana (5), tomato (9), and avocado (3) fruits. Baur et al. (3) demonstrated that the levels of applied, labeled methionine in avocado fruits dropped 60% during the respiratory climacteric rise. Similar results were reported by Yu et al. (18) with endogenous free methionine in tomato fruits.Although tomato fruits exhibit a respiratory climacteric rise, a mutant tomato fruit called ripening inhibitor (rin) has been developed that behaves like a nonclimacteric fruit and that produces very low amounts of ethylene (6, 1 0). McGlasson et al. (10) reported an increase in the respiratory rate of rin fruits treated with exogenous propylene (300-1000 ,ul/l), but the levels of endogenous ethylene remained very low. They also reported that the internal ethylene concentrations of attached mature green rin and normal fruits were similar.Mizrahi et al. (I 1) partially ripened rin mutant fruits by treating them with Ethephon ([2-chloroethyl]phosphonic acid) or ethylene gas (170 ,ul/l) while the fruits were still attached to the parent plant. These rin fruits developed one-third of the total lycopene produced by normal ripening fruits of the cultivar Rutgers. The treated rin fruits softened and developed some tomato fruit flavor. This paper reports on the levels of free methionine in rin and 'This study was supported in part by funds from CONACYT (Mexican Government). (12). Plants were pruned to two stems and staked. Two flowers were maintained per inflorescence and were tagged at anthesis. Mature green fruits were obtained from both lines 38 days after anthesis; in the field treatment, table ripe and yellow fruits were procured from normal and rin plants at 58 and 84 days after anthesis. Mature green fruits from both lines were green and had well developed gelatinous mater...