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.     

Mannosyl- and Xylosyl-Containing Glycans Promote Tomato (Lycopersicon esculentum Mill.) Fruit Ripening

The oligosaccharide glycans mannosylα1-6(mannosylα1-3)mannosylα1-6(mannosylα1-3) mannosylβ1-4-N-acetylglucosamine and mannosylα1-6(mannosylα1-3)(xylosylβ1-2) mannosylβ1-4-N-acetylglucosaminyl(fucosylα1-3) N-acetylglucosamine were infiltrated into mature green tomato fruit (Lycopersicon esculentum Mill., cv Rutgers). Coinfiltration of 1 nanogram per gram fresh weight of the glycans with 40 micrograms per gram fresh weight galactose, a level of galactose insufficient to promote ripening, stimulated ripening as measured by red coloration and ethylene production.     

Cell Wall Metabolism in Ripening Fruit (VII. Biologically Active Pectin Oligomers in Ripening Tomato (Lycopersicon esculentum Mill.) Fruits)

A water-soluble, ethanol-insoluble extract of autolytically inactive tomato (Lycopersicon esculentum Mill.) pericarp tissue contains a series of galacturonic acid-containing (pectic) oligosaccharides that will elicit a transient increase in ethylene biosynthesis when applied to pericarp discs cut from mature green fruit. The concentration of these oligosaccharides in extracts (2.2 [mu]g/g fresh weight) is in excess of that required to promote ethylene synthesis. Oligomers in extracts of ripening fruits were partially purified by preparative high-performance liquid chromatography, and their compositions are described. Pectins were extracted from cell walls prepared from mature green fruit using chelator and Na2CO3 solutions. These pectins are not active in eliciting ethylene synthesis. However, treatment of the Na2CO3-soluble, but not the chelator-soluble, pectin with pure tomato polygalacturonase 1 generates oligomers that are similar to those extracted from ripening fruit (according to high-performance liquid chromatography analysis) and are active as elicitors. The possibility that pectin-derived oligomers are endogenous regulators of ripening is discussed.     

1-甲基环丙烯采后处理对樱桃番茄果实成熟过程的影响

研究了不同浓度(0、0.035、0.07和0.11μL/L)的乙烯受体竞争性抑制剂1-甲基环丙烯(1-MCP)采后处理对绿熟期樱桃番茄的乙烯合成、果实软化、果实色素(叶绿素、茄红素、β-胡萝卜素)含量消长的影响.0.07 μL/L及其以上浓度的1-MCP降低了前期乙烯合成,同时推迟了乙烯释放高峰,但0.035 μL/L浓度的1-MCP处理并不能抑制内源乙烯合成.1-MCP显著延迟了果实软化和叶绿素降解,但并不影响这两个过程的启动.茄红素合成的启动和积累均受到了1-MCP抑制,而1-MCP并不推迟β-胡萝卜素合成的启动,只抑制其积累.这些结果提示了乙烯调节成熟生理过程的不同机制.对于绿熟期的樱桃番茄,0.07～0.11μL/L的1-MCP是实用的有效处理浓度.1-MCP有效浓度可能用于了解果实的乙烯受体水平和乙烯敏感性.     

Chromoplast-Targeted Proteins in Tomato (Lycopersicon esculentum Mill.) Fruit

The chloroplast to chromoplast transition during tomato (Lycopersicon esculentum Mill.) fruit ripening is characterized by a dramatic change in plastid structure and function. We have asked whether this process is mediated by an increase in the steady-state level of RNA for plastid targeted proteins. Assays for import of radiolabeled translation products into isolated pea (Pisum sativum L.) chloroplasts were used to monitor levels of chromoplast-targeted proteins at four stages of tomato fruit development. We have found striking increases during development in levels of translatable RNA for two such proteins. Additionally, the import of in vitro translation products was examined for seven individual cDNA clones known to encode RNA that increase during fruit ripening. Three of these clones produced in vitro translation products that were imported into pea chloroplasts. This implies that there is synthesis and import of new proteins during the transition from chloroplast to chromoplast and that the plastid conversion is an active developmental program rather than a simple decline in synthesis of the photosynthetic apparatus. Furthermore, our results demonstrate the utility of this method for identification of structural genes involved in plastid morphogenesis.     

Protein Phosphorylation in Plastids from Ripening Tomato Fruits {Lycopersicon esculentum)

Incubation of plastids isolated from ripening tomato fruits(Lycopersicon esculentum) with [     

Tomato (Lycopersicon esculentum Mill., cv. 'Better Bush') Plant Response to Root Restriction

Observations presented here describe changes in the growth ofLycopersicon esculentum Mill., cv. ‘Better Bush’,at the onset of root-restriction stress. Plants were grown ineither 1500 cm³ (control) or 25 cm³ (treated) containers ina flow-through hydroponic culture system (FTS). Seeds were imbibed,germinated, held for 13 d in sterile germination bags, thenplaced into the FTS and designated day zero plants. Plants grownin the FTS were harvested, every 7 d, from day 11 to day 46.Plant height, root and shoot weights, leaf areas, leaf lengths,branching and flowering were measured to illustrate morphologicalchanges that occurred in response to root-restriction stress.Plants restricted to a 25 cm³ root volume experienced a markedstress after 18 d in the FTS. A reduction in leaf elongationwas evident and preceded the time (prior to day 25) when maximumdry weights were attained by restricted root systems. Controlplants had greater leaf areas and plant dry weights than thoseof root-restricted plants after day 18. Treated plants showedno significant increase in dry weights from day 32 to the endof the experiment. Between day 18 and 25 the root: shoot ratiofor the treated plants dropped below that of the controls. Adventitiousrooting was evident in treated plants by day 25. Roots of thetreated plants showed an apparent waterlogging indicated bybrowning of roots by day 32. Root turnover followed as the primaryroot system was replaced by adventitious roots. The number ofbranches or flowers did not differ between control and treatedplants. The timing of the events described here can be usedto further the study of specific physiological responses oftomato plants to root-restriction stress.     

An Apparent Cellulase Complex in Tomato (Lycopersicon esculentum L.) Fruit

Four enzyme-containing fractions were separated by ammonium sulfate fractionation of 2-day, postbreaker tomato (Lycopersicon esculentum L. cv. Manhattan). The pH optima and substrate specificities are reported. The enzymes were identified as a nonspecific β-glucosidase, an exo-β-1,4-glucanase, and two endocellulases. Both endocellulase fractions were able to catalyze the hydrolysis of various insoluble cellulose materials.     

Products Released from Enzymically Active Cell Wall Stimulate Ethylene Production and Ripening in Preclimacteric Tomato (Lycopersicon esculentum Mill.) Fruit

Enzymically active cell wall from ripe tomato (Lycopersicon esculentum Mill.) fruit pericarp release uronic acids through the action of wall-bound polygalacturonase. The potential involvement of products of wall hydrolysis in the induction of ethylene synthesis during tomato ripening was investigated by vacuum infiltrating preclimacteric (green) fruit with solutions containing pectin fragments enzymically released from cell wall from ripe fruit. Ripening initiation was accelerated in pectin-infiltrated fruit compared to control (buffer-infiltrated) fruit as measured by initiation of climacteric CO₂ and ethylene production and appearance of red color. The response to infiltration was maximum at a concentration of 25 micrograms pectin per fruit; higher concentrations (up to 125 micrograms per fruit) had no additional effect. When products released from isolated cell wall from ripe pericarp were separated on Bio-Gel P-2 and specific size classes infiltrated into preclimacteric fruit, ripening-promotive activity was found only in the larger (degree of polymerization >8) fragments. Products released from pectin derived from preclimacteric pericarp upon treatment with polygalacturonase from ripe pericarp did not stimulate ripening when infiltrated into preclimacteric fruit.     

Tissue Culture Studies of Tomato (Lycopersicon esculentum)

Tomato is a major vegetable crop that has achieved tremendous popularity over the last century. It is grown in almost every country of the world. Development of protocols for in vitro selection can provide new advances for the production of stress tolerant cultivars. Techniques have been optimised for the production of haploids and somatic hybrids. Attempts have also been made to transfer the higher regenerative ability of wild varieties to cultivated tomatoes. Although, some information is available on the morphogenesis of tomato, the techniques have not been developed to a level at which they can be utilised in large-scale multiplication of commercially important cultivars. The morphogenesis response seems to be highly dependent PGRs used in the media, which is again cultivar and genotypic specific. Somatic embryogenesis in tomato is still at its infancy, and efficient procedures for large-scale production via somatic embryogenesis are yet to be developed. Genetic stability of the tissue culture raised tomato plants also needs to be addressed. The use of a combination of molecular and conventional breeding techniques could be the option for the development of cultivars resistant to biotic and abiotic stresses. This paper reviews the advances made in various aspects of tissue culture in tomato. It also discusses the issues that still need to be addressed to utilise the full potential of plant tissue culture techniques in genetic improvement and mass propagation of tomato.     

Tomato bushy stunt virus (TBSV) infecting Lycopersicon esculentum

Tomato bushy stunt virus (TBSV) was detected in tomato crop (Lycopersicon esculentum) in Egypt with characteristic mosaic leaf deformation, stunting, and bushy growth symptoms. TBSV infection was confirmed serologically by ELISA and calculated incidence was 25.5%. Basic physicochemical properties of a purified TBSV Egh isolate were identical to known properties of tombusviruses of isometric 30-nm diameter particles, 41-kDa coat protein and the genome of approximately 4800 nt. This is the first TBSV isolate reported in Egypt. Cloning and partial sequencing of the isolate showed that it is more closely related to TBSV-P and TBSV-Ch than TBSV-Nf and TBSV-S strains of the virus. However, it is distinct from the above strains and could be a new strain of the virus which further confirms the genetic diversity of tombusviruses.     

Novel Technique for Measuring Tissue Firmness within Tomato (Lycopersicon esculentum Mill.) Fruit

Developmental changes of tomato (Lycopersicon esculentum) fruit tissues during maturation were analyzed by a physically defined method (stress-relaxation analysis). The tip of a conical probe connected to a load sensor was positioned on the cut surface of a sliced tomato fruit, and the decay of the imposed stress was monitored. Stress-relaxation data thus obtained were used for the calculation of three stress-relaxation parameters. Different zones within tomato fruit harvested at six different ripening stages were analyzed. One of the stress-relaxation parameters, minimum stress-relaxation time (T₀), decreased as the fruits matured. The decrease in T₀ was first found in the core of the carpel junction within the endopericarp at the blossom end during the breaker stage. The decrease in T₀ progressed from the blossom end, through the equatorial region and finally throughout the shoulder, as the fruit matured. In mature green fruit, T₀ values within the placenta and the proximal carpel junction were lower than those by other parts of the fruit. For all measurements the maximum stress-relaxation time was not substantially changed during maturation, nor were their changes observed in different regions of the fruit. The observed relaxation rate was therefore correlated with softening. The results indicate that fruit softening may be physically associated with the stress-relaxation parameter, T₀, and the extent of softening is a function of position within the fruit. Decreases in T₀ value appear to be correlated with the reported regional variation in the appearance of polygalacturonase.     

Detection of nif Genes in Nitrogen-Fixing Bacterial Isolate from Tomato (Lycopersicon esculentum Mill cv Pusa Ruby)

Nitrogen-fixing bacterial isolate from the intercellular spaces of tomato root cortical cells was studied for the location of nif genes on the chromosomal or plasmid DNA. The bacterial isolate showed two plasmids of approximate molecular sizes of 220 and 120 kb. Klebsiella pneumoniae nif HDK probe hybridized with the chromosomal DNA and not with the plasmid DNA thereby showing that nif genes are localised on the chromosomal DNA.     

番茄"白化"突变体果实的几个生理生化特性检测

在番茄“白化”突变体果实发育过程中,总叶绿素、叶绿素a、叶绿素b的含量均小于正常植株的果实;果肉细胞内含有白色体;果实在贮藏期间的硬度较大。而果实品质,如糖酸比、维生素C和可溶性固形物的含量与正常果实差异不大。     

Polyuronides in Avocado (Persea americana) and Tomato (Lycopersicon esculentum) Fruits Exhibit Markedly Different Patterns of Molecular Weight Downshifts during Ripening

Avocado (Persea americana) fruit experience a rapid and extensive loss of firmness during ripening. In this study, we examined whether the chelator solubility and molecular weight of avocado polyuronides paralleled the accumulation of polygalacturonase (PG) activity and loss in fruit firmness. Polyuronides were derived from ethanolic precipitates of avocado mesocarp prepared using a procedure to rapidly inactivate endogenous enzymes. During ripening, chelator (cyclohexane-trans-1,2-diamine tetraacetic acid [CDTA])-soluble polyuronides increased from approximately 30 to 40 [mu]g of galacturonic acid equivalents (mg alcohol-insoluble solids)-1 in preripe fruit to 150 to 170 [mu]g mg-1 in postclimacteric fruit. In preripe fruit, chelator-extractable polyuronides were of high molecular weight and were partially excluded from Sepharose CL- 2B-300 gel filtration media. Avocado polyuronides exhibited marked downshifts in molecular weight during ripening. At the postclimacteric stage, nearly all chelator-extractable polyuronides, which constituted from 75 to 90% of total cell wall uronic acid content, eluted near the total volume of the filtration media. Rechromatography of low molecular weight polyuronides on Bio-Gel P-4 disclosed that oligomeric uronic acids are produced in vivo during avocado ripening. The gel filtration behavior and pattern of depolymerization of avocado polyuronides were not influenced by the polyuronide extraction protocol (imidazole versus CDTA) or by chromatographic conditions designed to minimize interpolymeric aggregation. Polyuronides from ripening tomato (Lycopersicon esculentum) fruit extracted and chromatographed under conditions identical with those used for avocado polyuronides exhibited markedly less rapid and less extensive downshifts in molecular weight during the transition from mature-green to fully ripe. Even during a 9-d period beyond the fully ripe stage, tomato fruit polyuronides exhibited limited additional depolymerization and did not include oligomeric species. A comparison of the data for the avocado and tomato fruit indicates that downshifts in polyuronide molecular weight are a prominent feature of avocado ripening and may also explain why molecular down-regulation of PG (EC 3.2.1.15) in tomato fruit has resulted in minimal effects on fruit performance until the terminal stages of ripening.