ABA和乙烯在草莓采后成熟衰老中的作用

随着草莓果实采后成熟衰老,ABA和乙烯生成迅速增长,乙烯累积与果实的变质腐烂程度呈正相关。ABA处理能增高纤维素酶活性和呼吸,而GA有抑制作用。ABA能促进乙烯、ACC生成,对MACC则无影响。GA_3抑制乙烯、ACC生成,促进MACC积累。CO_2对草莓有良好保鲜效果,并有效地抑制ABA和乙烯生成,低温下效果更为显著。     

Role of Ethylene in the Biosynthetic Pathways of Aroma Volatiles in Ripening Fruit

During the past decade, fruit aroma biosynthetic pathways were established in some climacteric fruits, such as tomato, apple, and melon. Inhibition of ethylene biosynthesis or its action in these fruits can reduce the production of fruit volatiles. Furthermore, ethylene partially regulates expression of a few important enzyme genes in fruit volatile biosynthetic pathways. The aim of this review is to bring together recent advances for understanding the regulatory role of ethylene in the biosynthesis of aroma volatiles in some fruits.     

Effect of Abscisic Acid on Banana Fruit Ripening in Relation to the Role of Ethylene

Abstract The role of abscisic acid (ABA) in banana fruit ripening was examined with the ethylene binding inhibitor, 1-methylcyclopropene (1-MCP). ABA (0, 10⁻⁵, 10⁻⁴, or 10⁻³ mol/L) was applied by vacuum infiltration into fruit. 1-MCP (1 μL/L) was applied by injecting a measured volume of stock gas into sealed glass jars containing fruit. Fruit ripening, as judged by ethylene evolution and respiration associated with color change and softening, was accelerated by 10⁻⁴ or 10⁻³ mol/L ABA. ABA at 10⁻⁵ mol/L had no effect. The acceleration of ripening by ABA was greater at 10⁻³ mol/L than at 10⁻⁴ mol/L. ABA-induced acceleration of banana fruit ripening was not observed in 1-MCP treated fruit, especially when ABA was applied after exposure to 1-MCP. Thus, ABA's promotion of ripening in intact banana fruit is at least partially mediated by ethylene. Exposure of ABA-treated fruit to 0.1 μL/L ethylene for 24 h resulted in increased ethylene production and respiration, and associated skin color change and fruit softening. Control fruit (no ABA) was unresponsive to similar ethylene treatments. The data suggest that ABA facilitates initiation and progress in the sequence of ethylene-mediated ripening events, possibly by enhancing the sensitivity to ethylene. Received 29 January 1999; accepted 16 January 2000     

乙烯受体在果实成熟及花衰老中的研究进展

乙烯受体是乙烯信号转导网络的第一个转导元件,通过调控受体基因的表达,可以调节植物对乙烯的敏感性,以调控果实的成熟及花衰老进程的响应.随着人们对乙烯受体研究的深入,乙烯受体突变体及受体抑制剂在采后果实和切花保鲜上的应用已受到广泛关注.就近年来关于乙烯受体的相关研究进展进行综述,重点介绍了乙烯受体的分子调控机制及乙烯受体在...     

Role of Ethylene in Avocado Fruit Development and Ripening: I. FRUIT DROP

A survey of avocado (Persea americana Mill.) fruit drop andethylene production was carried out during fruit development.Natural drop of avocado fruitlets started soon after set (May)and continued at a gradually decreasing rate until September,except for a temporarily increasing rate in late July. Fruitletsweighing up to 0?2 g dropped at a rate of over 30 percent perweek. With larger fruits, the rate was under 1 percent per week.Fruit drop ceased after September, when fruit growth declinedand the seed coat began to shrivel. A positive correlation was found between the rate of fruitletand fruit drop and ethylene production. Fruitlets with defectiveseeds produced ethylene at a very high rate of 7–10 timesmore than apparently normal fruits. The high incidence of defectiveseeds might be the cause of the very high levels of ethyleneproduction by young avocado fruitlets. The seed was found to be the main site of ethylene productionin fruitlets. Abscisic acid (ABA) levels in young abscissing fruits were 7times as high as those in non-abscissing fruits.     

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.     

The Synthesis of Ethylene in Melon Fruit during the Early Stage of Ripening

The levels of mRNA and polypeptide for a 1-aminocyclopropane-1-carboxylate(ACC) oxidase were studied to identify the tissues in whichthe synthesis of ethylene first occurs during the initial stageof ripening. RNA and immunoblot analysis showed that the levelsof the mRNA and polypeptide for ACC oxidase were very low inunripe fruit. They first became detectable in the placentaltissue at the pre-climacteric stage, and then their levels increasedin the mesocarp tissue during the climacteric increase in theproduction of ethylene. Two mRNAs for ACC synthase (transcribedfrom ME-ACS1 and ME-ACS2) were detected in the placental tissueand seeds at the pre-climacteric stage, but only the level ofME-ACS1 mRNA, which has been characterized as the mRNA for awound-inducible ACC synthase, increased in mesocarp, placentaltissues and seeds during ripening. The level of ME-ACS2 mRNAthat was isolated from etiolated seedlings of melon, did notchange markedly during ripening. These results suggest thatthe central region of melon fruit (placental tissue and seeds)plays a major role in the production of ethylene during theearly stage of ripening. ³These three authors made equal contribution to this study.     

Role of Brassinosteroids, Ethylene, Abscisic Acid, and Indole-3-Acetic Acid in Mango Fruit Ripening

Rapid ripening of mango fruit limits its distribution to distant markets. To better understand and perhaps manipulate this process, we investigated the role of plant hormones in modulating climacteric ripening of ??Kensington Pride?? mango fruits. Changes in endogenous levels of brassinosteroids (BRs), abscisic acid (ABA), indole-3-acetic acid (IAA), and ethylene and the respiration rate, pulp firmness, and skin color were determined at 2-day intervals during an 8-day ripening period at ambient temperature (21?±?1°C). We also investigated the effects of exogenously applied epibrassinolide (Epi-BL), (+)-cis, trans-abscisic acid (ABA), and an inhibitor of ABA biosynthesis, nordihydroguaiaretic acid (NDGA), on fruit-ripening parameters such as respiration, ethylene production, fruit softening, and color. Climacteric ethylene production and the respiration peak occurred on the fourth day of ripening. Castasterone and brassinolide were present in only trace amounts in fruit pulp throughout the ripening period. However, the exogenous application of Epi-BL (45 and 60?ng?g^?1 FW) advanced the onset of the climacteric peaks of ethylene production and respiration rate by 2 and 1?day, respectively, and accelerated fruit color development and softening during the fruit-ripening period. The endogenous level of ABA rose during the climacteric rise stage on the second day of ripening and peaked on the fourth day of ripening. Exogenous ABA promoted fruit color development and softening during ripening compared with the control and the trend was reversed in NDGA-treated fruit. The endogenous IAA level in the fruit pulp was higher during the preclimacteric minimum stage and declined during the climacteric and postclimacteric stages. We speculate that higher levels of endogenous IAA in fruit pulp during the preclimacteric stage and the accumulation of ABA prior to the climacteric stage might switch on ethylene production that triggers fruit ripening. Whilst exogenous Epi-BL promoted fruit ripening, endogenous measurements suggest that changes in BRs levels are unlikely to modulate mango fruit ripening.     

Glucose Inhibits ACC Oxidase Activity and Ethylene Biosynthesis in Ripening Tomato Fruit

Experiments were carried out to evaluate the effect of glucose on ripening and ethylene biosynthesis in tomato fruit (Lycopersicon esculentum Mill.). Fruit at the light-red stage were vacuum infiltrated with glucose solutions post-harvest and changes in 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, ACC, ACC oxidase, and ethylene production monitored over time. ACC oxidase activity was also measured in pericarp discs from the same fruits that were treated either with glucose, fructose, mannose, or galactose. While control fruit displayed a typical peak of ethylene production, fruit treated with glucose did not. Glucose appeared to exert its effect on ethylene biosynthesis by suppressing ACC oxidase activity. Fructose, mannose, and galactose did not inhibit ACC oxidase activity in tomato pericarp discs. Glucose treatment inhibited ripening-associated colour development in whole fruit. The extent of inhibition of colour development was dependent upon the concentration of glucose. These results indicate that glucose may play an important role in ethylene-associated regulation of fruit ripening.     

An Antisense Gene Stimulates Ethylene Hormone Production during Tomato Fruit Ripening

The ripening of many fruits is controlled by an increase in ethylene hormone concentration. E8 is a fruit ripening protein that is related to the enzyme that catalyzes the last step in the ethylene biosynthesis pathway, 1-aminocyclopropane-1-carboxylic (ACC) oxidase. To determine the function of E8, we have transformed tomato plants with an E8 antisense gene. We show here that the antisense gene inhibits the accumulation of E8 protein during ripening. Whereas others have shown that reduction of ACC oxidase results in reduced levels of ethylene biosynthesis, we find that reduction of the related E8 protein produces the opposite effect, an increase in ethylene evolution specifically during the ripening of detached fruit. Thus, E8 has a negative effect on ethylene production in fruit.     

Role of Ethylene in Avocado Fruit Development and Ripening: II. ETHYLENE PRODUCTION AND RESPIRATION BY HARVESTED FRUITS

Avocado (Persea americana Mill.) fruits were harvested at successivedevelopment stages during a period of 10 months. Ethylene productionand respiration were determined during the post-harvest period. Detached immature fruits were found to have a preclimactericincrease in ethylene production and respiration without anysigns of ripening. In fruits larger than 20 g a second phaseof climacteric ethylene production and respiration, associatedwith ripening, ensued. The preclimacteric ethylene was produced mainly by the seedcoat. It is suggested that the high ethylene production potentialof the seed coat may serve as a means for inducing abscissionin young fruits.     

Interrelationship of Polyamine and Ethylene Biosynthesis during Avocado Fruit Development and Ripening

Concentrations of polyamines (PA) and the activities of the PA-synthesizing enzymes ornithine decarboxylase (ODC) and arginine decarboxylase (ADC) extracted from the mesocarp tissue of avocado (Persea americana Mill, cv `Simmonds') fruits at different stages of development were compared with DNA content and the activities of 5′-methylthioadenosine (MTA) nucleosidase and 5-methylthioribose (MTR) kinase. Putrescine, spermidine, and spermine were at their peak concentrations during the early stages of fruit development (362, 201, and 165 nanomoles per gram fresh weight, respectively, at 15 days from full bloom), then declined to 30% or less at full maturity. Agmatine showed only a slight change in concentration throughout the fruit development. The activity of ODC, which was low during flowering (8 nmoles per milligram protein per hour), increased more than threefold during the first 2 months then declined at the later stages of fruit development, while ADC activity showed only a slight increase. DNA content followed a similar pattern of change as that of PA and ODC. The decline in DNA and ODC activity suggest a lack of correlation between cell proliferation and PA at the later stages of the avocado fruit development. It is also possible that any cell division which may take place during the latter stages of the fruit development is not sufficient to alter the pattern of PA biosynthesis. MTA nucleosidase and MTR kinase activities increased during the first 15 days of fruit development followed by a slight decline at 60 and 90 days from full bloom. At 120 days (1 month before full maturity) both MTA nucleosidase and MTR kinase activities increased significantly. During maximum ethylene synthesis, MTA nucleosidase and MTR kinase activities were approximately fivefold and eightfold, respectively, higher than during maximum PA synthesis. The data indicate that the MTA molecules produced during PA and ethylene synthesis are actively metabolized to MTR and MTR-1-P, the two intermediates involved in the regeneration of S-adenosylmethionine from MTA. The data also suggest that the PA and ethylene biosynthetic pathways are not actively competing for the same substrates at any given stage of the avocado fruit development and ripening.     

Changes in Adenosine Pyrophosphates in Cantaloupe Fruit Ripening Normally and after Treatment with Ethylene

During the climacteric rise in respiration of cantaloupe fruit(Cucumis melo L., var. reticulatus Naud.) the concentrationper gramme fresh weight of adenosine triphosphate (ATP) increasedand that of adenosine diphosphate (ADP) did not change; thusa net synthesis of adenosine pyrophosphate occurs during therespiratory climacteric. A net synthesis of protein which wasobserved was positively correlated with the concentration ofATP. Ethylene treatment stimulated a climacteric-like rise inthe respiration and in the rate of ripening in fruit harvestedat 9 to 32 days after anthesis. The ratio ATP/ADP increasedin fruit ripened with ethylene only when harvested 20 days ormore after anthesis.     

Ethylene and Wound-Induced Gene Expression in the Preclimacteric Phase of Ripening Avocado Fruit and Mesocarp Discs

Whereas intact postharvest avocado (Persea americana Mill.) fruit may take 1 or more weeks to ripen, ripening is hastened by pulsing fruit for 24 h with ethylene or propylene and is initiated promptly by cutting slices, or discs, of mesocarp tissue. Because the preclimacteric lag period constitutes the extended and variable component of the ripening syndrome, we postulated that selective gene expression during the lag period leads to the triggering of the climacteric. Accordingly, we sought to identify genes that are expressed gradually in the course of the lag period in intact fruit, are turned on sooner in response to a pulse, and are induced promptly in response to wounding (i.e. slicing). To this end, a mixed cDNA library was constructed from mRNA from untreated fruit, pulsed fruit, and aged slices, and the library was screened for genes induced by wounding or by pulsing and/or wounding. The time course of induction of genes encoding selected clones was established by probing northern blots of mRNA from tissues variously treated over a period of time. Four previously identified ripening-associated genes encoding cellulase, polygalacturonase (PG), cytochrome P-450 oxidase (P-450), and ethylene-forming enzyme (EFE, or 1-aminocyclopropane-1-carboxylic acid synthase), respectively, were studied in the same way. Whereas cellulase, PG, and EFE were ruled out as having a role in the initiation of the climacteric, the time course of P-450 induction, as well as the response of same to pulsing and wounding met the criteria[mdash]together with several clones from the mixed library[mdash]for a gene potentially involved in preclimacteric events leading to the onset of the climacteric. Further, it was established that the continuous presence of ethylene is required for persisting induction, and it is suggested that in selected cases wounding may exert a synergistic effect on ethylene action.