Changes in the Alkaloid Content of Developing Fruits of Tomato (Lycopersicon esculentum Mill.): I. ANALYSES OF CULTIVARS AND MUTANTS WITH DIFFERENT RIPENING CHARACTERISTICS

Normal ripening red-, orange- and yellow-fruited cultivars oftomato showed similar patterns of fruit growth and tomatineaccumulation to those of non-ripening mutants. In all fruits,the tomatine concentration declined continuously from an earlystage although the absolute amount per fruit showed a biphasicpattern of accumulation and decline. The turning point' occurredat an earlier developmental stage in normal fruits than in mutants.Normal fruits also had a lower initial and higher final tomatinecontent than mutants on a per fruit basis although, on a unitweight basis, their initial concentration was higher and finalconcentration lower. Small, prematurely-ripened red fruits hadalkaloid levels intermediate between large, unripe, green fruitsand large, ripe, red fruits. It is concluded that growth andripening processes may both contribute to the decline in fruittomatine. Key words: Tomato, Fruit ripening, Tomatine     

Sex Reversal and Fruit Formation on the Male Plants of Morus nigra L. by 2-Chloroethylphosphonic Acid

Ethrel treatment at 960, 1920, and 3840 parts 10–6 tomale plants of M. nigra produced intersex and female flowers.The intersexual flowers showed various degrees of transformationof male sex organs into female. The complete female flowersproduced were similar to female controls. Fruit setting occurredin inflorescences having both types of flowers which were similarin appearance but smaller in size than the untreated control.     

Development and Evaluation of an In Vitro System to Study Strawberry Fruit Development

Growth and ripening of strawberry (Fragariaananassa Duch.)fruit harvested at immature stages of development was accomplishedby placing the peduncles of individual fruit in solutions composedof hydroxyquinoline hemisulphate (HQS) and sucrose. Fruit cultivarand developmental stage at harvest were the major determinantsof in vitro performance. ‘Pajaro’ fruit harvestedat 50 to 60% maturity exhibited the greatest and most uniformweight gain when placed in solutions containing 200 mol m^–3HQS and 88 mol m^–3 sucrose. Although the final fruit weightof in vitro-ripened fruit was less than that of field-ripenedfruit, colour development in vitro occurred at the same rateand to the same extent as field-grown fruit. Key words: Ripening, non-climacteric fruit     

Maturation and Ripening of Fruit ofAmelanchier alnifoliaNutt. are Accompanied by Increasing Oxidative Stress

The extent of oxidative stress during ripening of saskatoon(AmelanchieralnifoliaNutt.) fruit was examined. Lipid peroxidation duringfruit development from the mature green to the fully ripe (purple)stage was evidenced by the accumulation of ethane and 2-thiobarbituricacid reactive substances. Fruit polar lipid and free fatty acidconcentrations also declined during ripening. Moreover, thedouble bond index of fatty acids in the polar lipid fractionfell during ripening, reflecting a progressive increase in thesaturation of membrane lipids. This increase in saturation waspartly due to a 65% decline in the concentration of linolenicacid. Activities of superoxide dismutase (SOD) and catalase(CAT) fell about 4-fold and 18-fold, respectively, during development,indicating higher potential for the accumulation of cytotoxicH₂O₂. Peroxidase activity remained relatively low and constantfrom the mature green to the dark red stage of development,then increased towards the end of ripening as fruits turnedpurple. Lipoxygenase (LOX) activity increased 2.5-fold fromthe mature green to the fully ripe stage. Tissue prints showedLOX to be present throughout fruit development and Western analysisrevealed that the increase in activity during ripening was dueto increased synthesis of the enzyme. Collectively, these resultsprovide evidence that ripening of this climacteric fruit isaccompanied by a substantial increase in free-radical-mediatedperoxidation of membrane lipids, probably as a direct consequenceof a progressive decline in the enzymatic systems responsiblefor catabolism of active oxygen species. The role of glutathione-mediatedfree-radical scavenging was also examined as a potential systemfor coping with this increased oxidative stress. Concentrationsof reduced and oxidized glutathione (GSSG) increased 2-foldand GSSG increased as a percentage of total glutathione, reflectingthe increase in oxidative status of fruits during ripening.Tissue prints of glutathione reductase (GRase) and transferase(GTase) showed these enzymes to be distributed throughout thepericarp at all stages of fruit development. GRase and GTaseactivities rose sharply during the later stages of fruit ripening,correlating well with substantial increases in the levels ofboth enzymes. Hence, the glutathione-mediated free-radical scavengingsystem was up-regulated towards the end of ripening, perhapsin response to the increasing oxidative stress resulting fromthe accumulation of lipid hydroperoxides from increased LOXactivity, in conjunction with a decline in SOD/CAT activities.Copyright1998 Annals of Botany Company Amelanchier alnifoliaNutt.; saskatoon fruit; ripening; oxidative stress.     

Responses of banana fruit to treatment with 1-methylcyclopropene

Experiments were conducted to determine levels of 1-methylcyclopropene (1-MCP) exposure needed to prevent ethylene-stimulated banana fruit ripening, characterise responses of ethylene-treated fruit to subsequent treatment with 1-MCP, and to test effects of subsequent ethylene treatment on 1-MCP-treated fruit softening. Fruit softening was measured at 20°C and 90% relative humidity. One hour exposure at 20°C to 1000 nl 1-MCP/l essentially eliminated ethylene-stimulated ripening effects. Exposure for 12 h at 20°C to just 50 nl 1-MCP/l was similarly effective. Fruit ripening initiated by ethylene treatment could also be delayed with subsequent 1-MCP treatment. However, 1-MCP treatment only slowed down ripening of ethylene-treated fruit when applied at 1 day after ethylene and was ineffective when applied 3 or 5 days after ethylene treatment. The ripening response of fruit treated with 1-MCP and subsequently treated with ethylene varied with interval time between 1-MCP and ethylene treatments. As time increased, the response of 1-MCP-treated fruit to ethylene was enhanced. Responses to 0.1, 1, 10 or 100 µl ethylene/l concentrations were similar. Enzyme kinetic analysis applied to 1-MCP effects on ethylene-induced softening of banana fruit suggested that 1-MCP inhibition is by noncompetitive antagonism of ethylene binding.     

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.     

Gibberellic acid causes earlier flowering and synchronizes fruit ripening of coffee

The effect of 100 mgl^–1 gibberellic acid (GA₃) on flowering and fruit ripening synchrony, fruit set, fruit fresh weight, and vegetative growth were studied for different size classes of coffee (Coffea arabica L. cv. Guatemalan) flower buds. Flower buds that were > 4 mm, but not developed to the candle stage at the time of GA₃ treatment, reached anthesis 20 days earlier than the controls, and their development was independent of precipitation, unlike the controls. Fruit from buds that were treated with GA₃ at the candle stage showed earlier and more synchronous ripening than the control, although no differences in flowering were found during anthesis. Buds that were smaller than 4 mm at the time of treatment did not respond to GA₃ applications. Treatment with GA₃ did not affect fruit set, fresh weight of fruits, or vegetative shoot growth.     

Seasonal Evolution of the Quality of Fresh Glasshouse Tomatoes under Mediterranean Conditions, as Affected by Air Vapour Pressure Deficit and Plant Fruit Load

Changes in yield and quality of fresh tomatoes in response toair vapour pressure deficit (VPD) and plant fruit load werestudied under Mediterranean summer conditions. Plants thinnedto three or six fruits per truss were grown in two compartments,one at a VPD below 1.5 kPa, the other without VPD control. Theseasonal trend in fruit yield and quality was assessed fromApril to September by weekly measurement of number, fresh weightand dry matter content of harvested fruits, together with theoccurrence of blossom-end-rot (BER) and cracking. On two occasions,in July and September, sugar and acid content was measured atthree ripening stages. The seasonal decrease in fresh yieldwas attenuated at low VPD, because of higher individual fruitfresh weight, especially at low fruit load. Low VPD decreasedoccurrence of BER but like low fruit load, it increased fruitcracking. Fruit dry matter content was lower at low VPD, butwas unaffected by fruit load. Sugar content and the ratio ofsugars:acids was increased at high VPD and low fruit load, withinteractive effects depending on season and ripening stage.The influence of VPD on acid content differed with fruit loadand also changed during ripening and between seasons. Resultsshowed that water was the main limiting factor for growth offruits picked in July; at this time, reducing fruit load topromote mean fruit size had negative effects on BER and cracking.Reducing VPD reduced BER but had a negative effect on crackingand diluted both the dry matter and sugar content. For fruitsharvested later in summer, these negative effects were attenuatedbecause fruit growth was also carbon limited. Copyright 2000Annals of Botany Company Lycopersicon esculentum Mill., tomato, water and carbon stress, yield, quality, dry matter, sugar, acid, BER, volatile composition     

Rooting of Chrysanthemum Stem Cuttings as Affected by (2-chloroethyl) Phosphonic Acid and Indolebutyric Acid

Stem cuttings of Chrysanthemum morifolium Ram. were treatedwith aqueous solutions of (2-chloroethyl)phosphonic acid (Ethrel)and indolebutyric acid (IBA). Ethrel (1 mg per 1) as a dip oras two foliar sprays, promoted root length and branching inMrs. Roy and Clipper which are difficult-to-root cultivars,but had no effect on Improved Mefo, an easy-to-root cultivar.IBA increased root number in both Clipper and Improved Mefo.The results suggest that IBA and Ethrel act at different stagesof the rooting process, with IBA promoting initiation and Ethrelstimulating elongation and branching. Increases in root numberwith IBA treatment, and in root length with Ethrel treatment,were accompanied by decreases in the soluble carbohydrate concentration,particularly in stem bases.     

Phytohormones in fruit development and maturation

Phytohormones are integral to the regulation of fruit development and maturation. This review expands upon current understanding of the relationship between hormone signaling and fruit development, emphasizing fleshy fruit and highlighting recent work in the model crop tomato (Solanum lycopersicum) and additional species. Fruit development comprises fruit set initiation, growth, and maturation and ripening. Fruit set transpires after fertilization and is associated with auxin and gibberellic acid (GA) signaling. Interaction between auxin and GAs, as well as other phytohormones, is mediated by auxin-responsive Aux/IAA and ARF proteins. Fruit growth consists of cell division and expansion, the former shown to be influenced by auxin signaling. While regulation of cell expansion is less thoroughly understood, evidence indicates synergistic regulation via both auxin and GAs, with input from additional hormones. Fruit maturation, a transitional phase that precipitates ripening, occurs when auxin and GA levels subside with a concurrent rise in abscisic acid (ABA) and ethylene. During fruit ripening, ethylene plays a clear role in climacteric fruits, whereas non-climacteric ripening is generally associated with ABA. Recent evidence indicates varying requirements for both hormones within both ripening physiologies, suggesting rebalancing and specification of roles for common regulators rather than reliance upon one. Numerous recent discoveries pertaining to the molecular basis of hormonal activity and crosstalk are discussed, while we also note that many questions remain such as the molecular basis of additional hormonal activities, the role of epigenome changes, and how prior discoveries translate to the plethora of angiosperm species.     

Modification of expansin protein abundance in tomato fruit alters softening and cell wall polymer metabolism during ripening

The role of the ripening-specific expansin Exp1 protein in fruit softening and cell wall metabolism was investigated by suppression and overexpression of Exp1 in transgenic tomato plants. Fruit in which Exp1 protein accumulation was suppressed to 3% that of wild-type levels were firmer than controls throughout ripening. Suppression of Exp1 protein also substantially inhibited polyuronide depolymerization late in ripening but did not prevent the breakdown of structurally important hemicelluloses, a major contributor to softening. In contrast, fruit overexpressing high levels of recombinant Exp1 protein were much softer than controls, even in mature green fruit before ripening commenced. This softening was correlated with the precocious and extensive depolymerization of structural hemicelluloses, whereas polyuronide depolymerization was not altered. These data are consistent with there being at least three components to fruit softening and textural changes. One component is a relaxation of the wall directly mediated by Exp1, which indirectly limits part of a second component due to polyuronide depolymerization late in ripening, perhaps by controlling access of a pectinase to its substrate. The third component is caused by depolymerization of hemicelluloses, which occurs independently of or requires only very small amounts of Exp1 protein.     

Free Sulfhydryl Groups in Ripening Fruits

Ripening was found to be accompanied by an increase in sulfhydryl (SH) group content in several fruits. In ripening, climacteric,tomato fruits, this increase was due mostly to an increase inthe glutathione level. In orange, a non-climacteric fruit, therelatively high SH levels did not change during developmentand maturation. Non-ripening tomato mutants, e.g., rin and nor,were characterized by low and constant SH levels during fruitgrowth and senescence. Ripening-inducing storage conditions,such as high temperature (30?C) and ethylene treatment, concomitantlyhastened the increase in SH level in fast-ripening tomato varieties.Storage conditions that slowed down the ripening process, suchas low temperatures (2, 12?C) and low oxygen levels (5%), sloweddown the increase in SH content. Storage of red tomatoes at30?C caused an increase in the SH content in comparison withlower temperature treatments (2, 12, 20?C). SH compounds (reducedglutathione, cysteine), dithiothreitol and an SH-binding compound(n-ethylmaleimide), did not affect the ripening process of greentomatoes. The results suggest that the increase in SH groupsaccompanies the ripening processes rather than regulating them. (Received April 26, 1982; Accepted September 6, 1982)     

Effect of Antisense Suppression of Endopolygalacturonase Activity on Polyuronide Molecular Weight in Ripening Tomato Fruit and in Fruit Homogenates

Fruit of tomato (Lycopersicon esculentum Mill.) in which endopolygalacturonase (PG) activity had been suppressed to <1% of wild-type levels were slightly firmer than nontransgenic controls later in ripening. Enzymically inactive cell walls were prepared from these ripening fruit using Tris-buffered phenol. When extracted with chelator followed by Na2CO3, the amounts of pectin solubilized from cell walls of nontransgenic control or from transgenic antisense PG fruit were similar. Size-exclusion chromatography analysis showed that, relative to controls, in antisense PG fruit polyuronide depolymerization was delayed in the chelator-soluble fraction throughout ripening and reduced in the Na2CO3-soluble fraction at the overripe stage. Reduced pectin depolymerization rather than altered extractability thus may have contributed to enhanced fruit firmness. Substantially larger effects of suppressed PG activity were detected in tomato fruit homogenates processed to paste. In control paste the majority of the polyuronide was readily soluble in water and was very highly depolymerized. In antisense PG paste the proportion of polyuronide solubilized by water was reduced, and polyuronides retained a high degree of polymerization. The suppression of fruit PG activity thus has a small effect on polyuronide depolymerization in the fruit but a much larger effect in paste derived from these fruit. This indicates that in the cell wall PG-mediated degradation of polyuronide is normally restricted but that in tissue homogenates or in isolated cell walls this restriction is removed and extensive pectin disassembly results unless PG is inactivated.     

The Role of Ethylene in the Shedding of Red Raspberry Fruit

The production of ethylene by red raspberry (Rubus idaeus L.cv. Glen Clova) fruit increased climacterically during development.The concentration of ethylene within green fruit was low butincreased substantially as fruit abscission and ripening commenced.The receptacle contained higher concentrations than the drupeletsat all stages measured. In the mature ripening fruit the ethyleneconcentrations were found to be physiologically significant,and would accelerate the abscission of large green non-abscisingfruit if supplied as a fumigant. The addition of ethylene toripe fruit did not accelerate abscission, probably because saturatinglevels occurred naturally within these fruit. Reduction of ethylenesynthesis rates using the inhibitor of ethylene production aminoethoxyvinylglycine(AVG) reduced the rate of abscission zone weakening which occursin detached large green fruit. The rate of ethylene productionwas found to be dependent on the supply of the precursor l-aminocyclopropane-l-carboxylicacid (ACC). This only accumulated to any extent in those ripefruit with high rates of ethylene production. Rubus idaeus, raspberry, abscission, fruit ripening, ethylene, aminocyclopropane-l-carboxylic acid     

Polyamine content of long-keeping alcobaca tomato fruit

Fruit of tomato landrace Alcobaca, containing the recessive allele alc, ripen more slowly, with a reduced level of ethylene production, and have prolonged keeping qualities. The levels of polyamines in pericarp tissues of alc and `wild type' Alc (cv Rutgers and Alcobaca-red) fruit were measured by HPLC in relation to ripening. Putrescine was the predominant polyamine with a lower content of spermidine, while spermine was just detectable. The level of putrescine was high at the immature green stage and declined in the mature green stage. In Alc fruit the decline persisted but in alc fruit the putrescine level increased during ripening to a level similar to that present at the immature green stage. There was no pronounced change or difference in spermidine levels. The enhanced polyamine level in alc fruit may account for their ripening and storage characteristics.     

Protein synthesis in relation to ripening of pome fruits

Protein synthesis by intact Bartlett pear fruits was studied with ripening as measured by flesh softening, chlorophyll degradation, respiration, ethylene synthesis, and malic enzyme activity. Protein synthesis is required for normal ripening, and the proteins synthesized early in the ripening process are, in fact, enzymes required for ripening. ¹⁴C-Phenylalanine is differentially incorporated into fruit proteins separated by acrylamide gel electrophoresis of pome fruits taken at successive ripening stages. Capacity for malic enzyme synthesis increases during the early stage of ripening. Fruit ripening and ethylene synthesis are inhibited when protein synthesis is blocked by treatment with cycloheximide at the early-climacteric stage. Cycloheximide became less effective as the climacteric developed. Ethylene did not overcome inhibition of ripening by cycloheximide. The respiratory climacteric is not inhibited by cycloheximide. It is concluded that normal ripening of pome fruits is a highly coordinated process of biochemical differentiation involving directed protein synthesis.     

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 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.