Ethylene-Enhanced 1-Aminocyclopropane-1-carboxylic Acid Synthase Activity in Ripening Apples

Regulation by Carbon Dioxide of Wound-induced Ethylene Biosynthesis in the Peel of Citrus Fruit

The effect of carbon dioxide (CO2) on wound-induced ethylene biosynthesis in flavedo discs of mature orange fruits (Citrus sinensis L. Osbeck) is investigated. Wounding induced a marked and rapid increase on the rate of ethylene production, the content of 1-aminocyclopropane-1-carboxylic acid (ACC) and on the in vivo ACC oxidase (ACO) activity. Incubation of flavedo discs in a 15% CO2 atmosphere suppressed activation of these processes. Wound-induced ethylene production was inhibited by CO2 in a concentration-dependent manner but ACO activity was enhanced at concentrations between 1% and 5%. Kinetic analysis of the interaction between CO2 and ACO activity indicated that high CO2 acted as a noncompetitive inhibitor. Removal of CO2 after 24 h incubation did not restore normal rates of ethylene production. CO2 partially counteracted the increase in ethylene production and ACO activity induced by a pretreatment with an ethylene action inhibitor (STS, silver thiosulfate). This suggested that part of CO2 action on ethylene biosynthesis might be due to interfering ethylene action. Collectively, the results indicated that ACS activity appeared to be the major regulatory step by which CO2 suppresses wound-induced ethylene production. ACO was differentially modulated by CO2, which is being stimulated at low concentrations and inhibited at high concentrations.

Role of internal atmosphere on fruit ripening and storability-a review

Concentrations of different gases and volatiles present or produced inside a fruit are determined by the permeability of the fruit tissue to these compounds. Primarily, surface morphology and anatomical features of a given fruit determine the degree of permeance across the fruit. Species and varietal variability in surface characteristics and anatomical features therefore influence not only the diffusibility of gases and volatiles across the fruits but also the activity and response of various metabolic and physiological reactions/processes regulated by these compounds. Besides the well-known role of ethylene, gases and volatiles; O2, CO2, ethanol, acetaldehyde, water vapours, methyl salicylate, methyl jasmonate and nitric oxide (NO) have the potential to regulate the process of ripening individually and also in various interactive ways. Differences in the prevailing internal atmosphere of the fruits may therefore be considered as one of the causes behind the existing varietal variability of fruits in terms of rate of ripening, qualitative changes, firmness, shelf-life, ideal storage requirement, extent of tolerance towards reduced O2 and/or elevated CO2, transpirational loss and susceptibility to various physiological disorders. In this way, internal atmosphere of a fruit (in terms of different gases and volatiles) plays a critical regulatory role in the process of fruit ripening. So, better and holistic understanding of this internal atmosphere along with its exact regulatory role on various aspects of fruit ripening will facilitate the development of more meaningful, refined and effective approaches in postharvest management of fruits. Its applicability, specially for the climacteric fruits, at various stages of the supply chain from growers to consumers would assist in reducing postharvest losses not only in quantity but also in quality.

Changes in free and conjugated polyamines during starvation of sugarcane juices as analyzed by high-performance liquid chromatography

Changes of the polyamines (PAs) titer in high- and mid-molecular-mass carbohydrates (HMMCs and MMMCs, respectively) obtained from sugarcane juices stored for 72 h at pH 5.2 or clarified at pH 8.0 have been studied. Cadaverine (CAD) is the most abundant free (S) PA in the MMMC fraction from juices at pH 5.2, whereas putrescine (PUT) was revealed as the main PA at pH 8.0. A slight increase in the free PUT titer can be noted at pH 5.2 for 72 h of juice starvation. PAs from MMMC were mainly conjugated to acid-insoluble (PH) molecules. Accumulation of PH-PAs with the time of starvation was especially significant for PUT and CAD. However, CAD has also been detected in the acid-soluble (SH) fraction and its concentration increases with the time of starvation at pH 5.2. The accumulation pattern of free and conjugated PAs from HMMCs is similar to that found for MMMCs although some differences can be observed. For instance, the increase in free PUT with the time at pH 8.0 was 2.7-times higher in the HMMC fraction than in the MMMC fraction. Conjugated PAs associated to acid-soluble macromolecules (SH fraction) achieved a level in HMMC fractions higher than that observed in the MMMC fraction. Moreover, the reported increase with time that was observed in PH-CAD from the MMMC fraction was not observed in the HMMC fraction, and, finally, the increase in PH-PUT with the time was lower for the HMMC fraction than for the MMMC fraction.

Induction by Electric Currents of Ethylene Biosynthesis in Cucumber (Cucumis sativus L.) Fruit

The effects of an electric current on ethylene biosynthesis were investigated in cucumber (Cucumis sativus L.) fruit that were producing almost no ethylene. Direct currents at 0.5 to 3.0 milliamperes induced much ethylene synthesis, with a rapid continuous increase in the rate, which reached a peak within 5 to 6 hours and then decreased. The rate of production was greater with a stronger current. Ethylene production was not observed after the use of a sine-wave alternating current (60 hertz) at 3 milliamperes, the magnitude at which a direct current had the greatest effect. The activity of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase and ethylene forming enzyme (EFE) increased before the rise in ethylene production. ACC synthase and EFE were activated sixfold and fourfold, respectively, by 2 hours. The concentration of ACC increased linearly up to 6 hours and then decreased. Ethylene induction by an electric current was suppressed almost completely by the infiltration of the cucumbers with 5 millimolar aminooxyacetic acid, an inhibitor of ACC synthase, and was also suppressed 70% by 5 millimolar salicylic acid, an inhibitor of EFE. The results indicate that the ethylene induced by the direct current was synthesized via the ACC-ethylene pathway as a result of electrical stress, a new kind of stress to be identified.

Effect of 2,5-Norbornadiene upon Ethylene Biosynthesis in Midclimacteric Carnation Flowers

The climacteric increase in ethylene production in carnation (Dianthus caryophyllus L. cv White Sim) flowers is known to be accompanied by an increase in 1-aminocyclopropane-1-carboxylate (ACC) synthase and ethylene forming enzyme (EFE) activities. When midclimacteric flowers were exposed to 2,5-norbornadiene, which blocks ethylene action, ethylene production began to decrease after 2 to 3 hours. ACC synthase activity was markedly reduced after 4 hours and the increase in EFE activity was blocked indicating that the autocatalytic signal associated with ethylene action stimulates both enzyme activities.

Regulation of Ethylene Biosynthesis in Avocado Fruit during Ripening

Preclimacteric avocado (Persea americana Mill.) fruits produced very little ethylene and had only a trace amount of l-aminocyclopropane-1-carboxylic acid (ACC) and a very low activity of ACC synthase. In contrast, a significant amount of l-(malonylamino)cyclopropane-1-carboxylic acid (MACC) was detected during the preclimacteric stage. In harvested fruits, both ACC synthase activity and the level of ACC increased markedly during the climacteric rise reaching a peak shortly before the climacteric peak. The level of MACC also increased at the climacteric stage. Cycloheximide and cordycepin inhibited the synthesis of ACC synthase in discs excised from preclimacteric fruits. A low but measurable ethylene forming enzyme (EFE) activity was detected during the preclimacteric stage. During ripening, EFE activity increased only at the beginning of the climacteric rise. ACC synthase and EFE activities and the ACC level declined rapidly after the climacteric peak. Application of ACC to attached or detached fruits resulted in increased ethylene production and ripening of the fruits. Exogenous ethylene stimulated EFE activity in intact fruits prior to the increase in ethylene production. The data suggest that conversion of S-adenosylmethionine to ACC is the major factor limiting ethylene production during the preclimacteric stage. ACC synthase is first synthesized during ripening and this leads to the production of ethylene which in turn induces an additional increase in ACC synthase activity. Only when ethylene reaches a certain level does it induce increased EFE activity.

Ethylene-promoted conversion of 1-aminocyclopropane-1-carboxylic Acid to ethylene in peel of apple at various stages of fruit development

Internal ethylene concentration, ability to convert 1-amino-cyclopropane-1-carboxylic acid (ACC) to ethylene (ethylene-forming enzyme [EFE] activity) and ACC content in the peel of apples (Malus domestica Borkh., cv Golden Delicious) increased only slightly during fruit maturation on the tree. Treatment of immature apples with 100 microliters ethylene per liter for 24 hours increased EFE activity in the peel tissue, but did not induce an increase in ethylene production. This ability of apple peel tissue to respond to ethylene with elevated EFE activity increased exponentially during maturation on the tree. After harvest of mature preclimacteric apples previously treated with aminoethoxyvinyl-glycine, 0.05 microliter per liter ethylene did not immediately cause a rapid increase of development in EFE activity in peel tissue. However, 0.5 microliter per liter ethylene and higher concentrations did. The ethylene concentration for half-maximal promotion of EFE development was estimated to be approximately 0.9 microliter per liter. CO(2) partially inhibited the rapid increase of ethylene-promoted development of EFE activity. It is suggested that ethylene-promoted CO(2) production is involved in the regulation of autocatalytic ethylene production in apples.