Metabolic Studies with Banana Fruit Slices II. Effects of Inhibitors on Respiration, Ethylene Production, and Ripening

100

Fruits of Lycopersicon escukntum Mill cv Sonatine stored in 6% C02, 6% 02, and 88% N2 for 14 weeks at 12°C, exhibited a temporal separation of certain biochemical events associated with ripening.The specific activity of two citric acid cycle enzymes, citrate synthase and malate dehydrogenase, fell substantially during the first 2 weeks of storage when changes in organic acid concentration also occurred. During this period, lycopene, polygalacturonase, and ethylene were undetectable.When fruit were removed from store, ethylene was evolved and polygalacturonase and invertase activity were rapidly initiated as was synthesis of lycopene.To determine whether the changes in organic acid metabolism were affected by ethylene, fruit was kept at 22°C in either a normal atmosphere or a normal atmosphere supplemented with 27 microliters per liter of ethylene, and it was shown that in both atmospheres similar quantitative changes to those described above occurred in the citric acid cycle enzymes specific activities before any detectable increase in the specific activities of invertase and polygalacturonase. These latter changes, together with pigment changes, occurred between 2 and 3 days earlier in fruit exposed to ethylene, compared with those kept in a normal atmosphere.

mentioning

confidence: 99%

Ethylene-Independent and Ethylene-Dependent Biochemical Changes in Ripening Tomatoes

Jeffery¹,

Smith²,

Goodenough³

et al. 1984

100

“…On these observations it has been suggested that glycolysis is accelerated in the course of the climacteric rise in respiration (6,15,40). However, activation of glycolysis per se cannot be the cause of ripening or even of the climacteric, because anaerobiosis, while enhancing glycolysis in avocados (see below) and apples (11), prevents ripening, and uncouplers of oxidative phosphorylation, which enhance respiration and presumably glycolysis in banana slices, neither accelerate ripening nor inhibit it when ripening is induced by ethylene or occurs naturally (31,42). Furthermore, the postulated augmentation of glycolysis during the climacteric cannot be attributed to uncoupling of oxidative phosphorylation, for both the rates of 32P esterification and the levels of ATP increase during the climacteric in a variety of fruits (38,43).…”

mentioning

confidence: 99%

“…Ethylene is considered to be the agent that triggers the climacteric and fruit ripening (34). It is questionable whether protein synthesis constitutes a requisite for the climacteric rise, because the stimulation of glycolysis in preclimacteric fruits by anoxia (11), the acceleration of respiration in preclimacteric slices by uncouplers of oxidative phosphorylation (33), the demonstration of full respiratory capacity of isolated mitochondria from preclimacteric tissue (29), and the development of the climacteric under conditions which may be thought to preclude synthesis of protein (18,31,42), all indicate that the enzymatic capacity of preclimacteric fruits may be adequate to sustain the rates of respiration observed at the height of the climacteric.…”

mentioning

confidence: 99%

“…It is questionable whether protein synthesis constitutes a requisite for the climacteric rise, because the stimulation of glycolysis in preclimacteric fruits by anoxia (11), the acceleration of respiration in preclimacteric slices by uncouplers of oxidative phosphorylation (33), the demonstration of full respiratory capacity of isolated mitochondria from preclimacteric tissue (29), and the development of the climacteric under conditions which may be thought to preclude synthesis of protein (18,31,42) these observations it has been suggested that glycolysis is accelerated in the course of the climacteric rise in respiration (6,15,40). However, activation of glycolysis per se cannot be the cause of ripening or even of the climacteric, because anaerobiosis, while enhancing glycolysis in avocados (see below) and apples (11), prevents ripening, and uncouplers of oxidative phosphorylation, which enhance respiration and presumably glycolysis in banana slices, neither accelerate ripening nor inhibit it when ripening is induced by ethylene or occurs naturally (31,42). Furthermore, the postulated augmentation of glycolysis during the climacteric cannot be attributed to uncoupling of oxidative phosphorylation, for both the rates of 32P esterification and the levels of ATP increase during the climacteric in a variety of fruits (38,43).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Similarities between the Actions of Ethylene and Cyanide in Initiating the Climacteric and Ripening of Avocados

Solomos¹,

Laties²

1974

A continuous exposure of intact avocados (Persea americana) to 400 ul/l of cyanide results in a rapid increase in the rate of respiration, followed by a rise in ethylene production, and eventual ripening. The pattern of changes in the glycolytic intermediates glucose 6-phosphate, fructose diphosphate, 3-phosphoglyceric acid, and phosphoenolpyruvate during the rapid rise in respiration in both ethylene and cyanide-treated fruits is similar to that found in fruits made anaerobic where a 2.3-to 3-fold increase in the rate of glycolysis is observed. It is suggested that both during the climacteric and in response to cyanide, glycolysis is enhanced. It is proposed that cyanide implements the diversion of electrons to the cyanide-resistant electron path through structural alterations which are independent of the simultaneous inhibition of cytochrome oxidase.The sharp rise in respiration, the climacteric, which attends the ripening of certain fruits, has been attributed alternatively to a decrease in the "organization resistance" of the cell (11,27) and to an increase in protein synthesis, particularly to the synthesis of one or more enzymes putatively involved in the ripening process (1,17,36). Ethylene is considered to be the agent that triggers the climacteric and fruit ripening (34). It is questionable whether protein synthesis constitutes a requisite for the climacteric rise, because the stimulation of glycolysis in preclimacteric fruits by anoxia (11), the acceleration of respiration in preclimacteric slices by uncouplers of oxidative phosphorylation (33), the demonstration of full respiratory capacity of isolated mitochondria from preclimacteric tissue (29), and the development of the climacteric under conditions which may be thought to preclude synthesis of protein (18,31,42) these observations it has been suggested that glycolysis is accelerated in the course of the climacteric rise in respiration (6,15,40). However, activation of glycolysis per se cannot be the cause of ripening or even of the climacteric, because anaerobiosis, while enhancing glycolysis in avocados (see below) and apples (11), prevents ripening, and uncouplers of oxidative phosphorylation, which enhance respiration and presumably glycolysis in banana slices, neither accelerate ripening nor inhibit it when ripening is induced by ethylene or occurs naturally (31,42). Furthermore, the postulated augmentation of glycolysis during the climacteric cannot be attributed to uncoupling of oxidative phosphorylation, for both the rates of 32P esterification and the levels of ATP increase during the climacteric in a variety of fruits (38,43). Because enhancement of glycolysis appears to attend ripening under conditions which normally call for its diminution, i.e. where there is an elevation in energy charge (2, 43), and because the fruit-ripening hormone, ethylene, enhances glycolysis in yeast (41), we undertook to study, in addition to the effect of ethylene on glycolysis, the effect of cyanide on both glycolysis and ripening; because on the o...

“…19). It has been used for ripening studies in bananas (7,18,21), tomatoes (15,16,22), avocados (3,19), and apples (8,9). These studies usually involve incubating the fruit slice in an aqueous medium of the test substance.…”

mentioning

confidence: 99%

The Effect of Tonicity and Metabolic Inhibitors on Respiration and Ripening of Avocado Fruit Slices

Tingwa¹,

Young²

1974

The ripening of avocado (Persea americana Mill.) fruit slices was inhibited whether they were floated in water or in buffered aqueous 0.3 M mannitol, 0.25 M KCI, and sucrose. There was no evidence to support the contention that ripening occurred when the tonicity of the bathing medium was increased. Decreased gaseous exchange is considered to be a major cause of this inhibition because by utilizing a technique that afforded better aeration, slices could be water infiltrated and still ripen normally. Metabolic studies on the ripening of slices using this method in- (15,16,22), avocados (3,19), and apples (8, 9). These studies usually involve incubating the fruit slice in an aqueous medium of the test substance. Floating the fruit slices in water is known to cause, among other things, decline in respiration (10, 20), impairment of ethylene production (9, 10), swelling (3, 8), and leakage of cell contents (3,7,22 MATERIALS AND METHODSWater and Tonicity Experiments. In this study the incubation media whose effects were to be tested consisted of moist air, H20, 0.3 M mannitol, 0.25 M KCl, and 0.4 M sucrose. The latter four media were adjusted to pH 6.5 with 0.15 M potassium phosphate buffer, and 25 jug/l streptomycin sulfate were added as a safeguard against microbial infection.One avocado (Persea americana Mill.) fruit of the Hass variety was selected and its surface was sterilized initially by rubbing with 70% (v/v) ethanol and followed by washing for 5 min in 1:3 dilution of Clorox (sodium hypochlorite 1.9 w/v available chlorine) as outlined by Palmer et al. (21). With the aid of a cork borer and razor blade, slices 1 cm wide and 1 mm thick were prepared. The slices were rinsed for 2 min in sterile H10, dried gently with filter paper, and put in groups of four (weighing 0.8-0.9 g) per Warburg flask. There were four flasks per treatment, each containing 3 ml of the treatment medium. For moist air, the flasks contained only moist filter paper. Respiration was measured at 20 C using a Gilson respirometer. The CO2 produced was trapped by 3 M KOH in the center well of the Warburg flasks. All equipment used was autoclaved, and tissue slicing was done in a transfer hood under aseptic conditions.Slice Thickness and Infiltration Experiments. Under the same aseptic conditions as above 2, 4, 7, and 10 mm thick rectangular slices were cut from two uniform Hass fruits. Each slice was 2.5 cm long and, while the peel was left attached, the seed coat was cut away. Sterile water was vacuum infiltrated (500 mm Hg) into half the number of slices of each size for varying periods of 12, 20, 30, and 60 sec for the 2, 4, 7, and 10 mm thick slices, respectively. A period of 60 sec was allowed for water to move in the tissue. In this way, an increased weight of about 6% was achieved for all sizes. Incubation was carried out utilizing a technique developed by Laties (personal communication) in which a continuous flow of moisture, or any substance, to a tissue is facilitated by a strip of lens paper through the wick effect. Both u...