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.     

Effects of CCC on the Formation and Abortion of Flowers in the First Inflorescence of Tomato (Lycopersicon esculentum Mill.)

Treatment of tomato plants with (2-chloroethyl)trimethylammoniumchloride (CCC) reduced their growth in height and d. wt andincreased the number of flowers formed in the first inflorescence.In plants grown at a high temperature with low light, applicationof CCC reduced the incidence of flower abortion in the firstinflorescence. Effects of -cyclopropyl--(4-methoxyphenyl)--(pyrimidin-5-yl)methanol(ancymidol) were similar to those of CCC while a third growthretardant, N-dimethylaminosuccinamic acid (B-9), was effectivein reducing growth in height but was without apparent effecton flower number or flower abortion. An interaction occurred between CCC and GA₃ such that effectsof CCC on growth and flowering were reduced when GA was alsoapplied. Yields of diffusible gibberellin-like substances fromthe shoot tips were markedly reduced by treating plants withCCC but were apparently not affected by treating plants withB-9. It is suggested that effects of CCC on flowering in tomatoare mediated, in part at least, through changes in levels ofendogenous gibberellins.     

Control of Flower Number in the First Inflorescence of Tomato (Lycopersicon esculentum Mill.): The Role of Gibberellins

The number of flowers in the first inflorescence of tomato plantswas increased by low temperatures and reduced by the applicationof GA³. The effect of GA³, was greater in a low temperatureregime (12 °C minimum) than at normal temperatures (16 °Cminimum). Increases in flower number could be produced by theremoval of young developing leaves but the treatment was nolonger effective if plants wen grown at low temperatures orwere treated with GA³. Young developing leaves were shown to be sources of diffusiblegibberellin-like substances. Leaves from plants grown in a normaltemperature regime yielded greater amounts of gibberellin-likesubstances than leaves from plants grown in the low temperatureregime. It is suggested that high levels of endogenous gibberellinsact to reduce the number of flowers formed in the first inflorescence,and that leaf removal and low temperatures influence flowernumbers by lowering levels of diffusible gibberellins in theplants. Lycopersicon esculentum, tomato, flower number, gibberellins, temperature     

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.     

Growth and Water Relations of Wilty Mutants of Tomato (Lycopersicon esculentum Mill.)

In contrast to some previous reports on the growth of the ABA-deficientwilty mutants of tomato, growth was at least as rapid in themutants as in the wild type, as long as an adequate plant waterstatus was maintained by growing the plants under mist. Moreover,shoot extension was greater and the rate of leaf productionmore rapid in the mutants. Stomatal changes in response to environmentand to time in the light-dark cycle were generally similar inboth wilty mutants and the wild type, though the wild-type weregenerally more closed. Grafting experiments confirmed that thegenotype of the shoot was dominant in determining stomatal aperture,though wild-type rootstocks could cause a slight reduction inthe stomatal conductance of mutant leaves. The effect on plantwater relations of draughting only part of the root system wasinvestigated in a ‘split-root’ experiment. Withholdingwater from only part of the root system was found to lower significantlythe mean leaf water potential, even though the potential evaporationrate was kept very small. Key words: Abscisic acid, stomata, tomato     

Compartments and Permeability for Potassium in Developing Fruits of Tomato (Lycopersicon esculentum Mill.)

Permeabilities of plasmalemma and tonoplast, and the distributionof potassium between free space, cytoplasm, and vacuole, wereestimated from the kinetics of the efflux of potassium fromslices of tomato pericarp. The permeabilities of plasmalemmaand tonoplast did not change during development, but the proportionof potassium in the cytoplasm increased during ripening. Itis suggested that the effects of ethylene, and the changes takingplace during ripening are not caused by changing permeabilitiesof membranes. Increasing activities of ions in the cytoplasm,rather than increasing membrane permeabilities, may explainprevious observations that the efflux of solutes from fruittissues increases during ripening.     

Gibberellins and the Early Disease Syndrome of Aspermy Virus in Tomato (Lycopersicon esculentum Mill.)

A quantitative examination of the development of the diseasesyndrome created by as permyvirus in tomato (Lycopersicon esculentumMill., cultivar Potentate) revealed an early reduction in subapicalmitotic activity which led to the development of smaller internodes.Later symptoms were associated with necrosis of young axillarybuds and the failure of a new vegetative apex to develop onceflower initiation had begun in the primary apical bud. Application of gibberellic acid (GA₃) to the growing point tendedto reverse virus-induced stunting by increasing cell expansionbut the response was less than that in healthy plants. Thiswas due to a reduction in the number of mitoses associated withvirus infection. No consistent difference was found betweenthe endogenous gibberellin levels of healthy and infected plants.It is suggested that the most important single factor in earlysymptom development is a virus-induced reduction in cell divisionwhich cannot be overcome by applying GA₃.     

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.     

Reduction in Pectin Methylesterase Activity Modifies Tissue Integrity and Cation Levels in Ripening Tomato (Lycopersicon esculentum Mill.) Fruits

Pectin methylesterase (PME, EC 3.1.1.11) is an ubiquitous enzyme in the plant kingdom; however, its role in plant growth and development is not yet understood. Using transgenic tomato (Lycopersicon esculentum Mill.) fruits that show more than 10-fold reduction in PME activity because of expression of an antisense PME gene, we have investigated the role of PME in tomato fruit ripening. Our results show that reduced PME activity causes an almost complete loss of tissue integrity during fruit senescence but shows little effect on fruit firmness during ripening. Low PME activity in the transgenic fruit pericarp modified both accumulation and partitioning of cations between soluble and bound forms and selectively impaired accumulation of Mg2+ over other major cations. Decreased PME activity was associated with a 30 to 70% decrease in bound Ca2+ and Mg2+ in transgenic pericarp. Levels of soluble Ca2+ increase 10 to 60%, whereas levels of soluble Mg2+ and Na+ are reduced by 20 to 60% in transgenic pericarp. Changes in cation levels associated with lowered PME activity do not affect the rate of respiration or membrane integrity of fruit during ripening. Overall, these results suggest that PME plays a role in determining tissue integrity during fruit senescence, perhaps by regulating cation binding to the cell wall.     

Studies on two Gibberellin-like Substances in Young Shoots of Tomato (Lycopersicon esculentum Mill.)

Two gibberellin-like substances were found in the acidic fractionof shoot extracts of the tomato (Lycopersicon esculentum Mill.,cultivar Potentate). These were resolved by paper chromotographywith iso-propanol/ammonia/water (10:1:1) as the developing solventbut not with n-butanol/1.5 N ammonia (3:1). Both substanceswere active in the dwarf maize bioassay on mutants d-1, d-2,d-3, and d-5, and appeared to be more active on d-5 than d-1.Neither was active in the Meteor Pea assay. Neutral and basicfractions were inactive. The relative amounts of these two substances varied accordingto the age of the tissues from which they were extracted andthis feature is discussed in relation to future studies on thephysiology of gibberellin-like substances in vivo.     

Constant, Fluctuating and Effective Temperature and Seed Longevity: a Tomato (Lycopersicon esculentum Mill.) Exemplar

Tomato seeds with a moisture content of 16.4% were stored hermeticallyat one of five constant temperatures (10, 20, 30, 40, 50 °C)or in one of nine alternating temperature (24 h/24 h) regimes(10/30, 10/40, 10/50, 20/30, 20/40, 20/50, 30/40, 30/50, 40/50°C) for up to 224 d. In each regime, seed survival conformedto cumulative negative normal distributions and all 14 survivalcurves could be constrained to a common origin. Estimates ofthe constants C_Hand C_Qof the viability equation determined atconstant temperatures were 0.0346 (s.e. 0.0058) and 0.000401(s.e. 0.000096), respectively. The effective temperature forseed survival of each alternating temperature regime was alwaysmuch higher than the mean. Tomato seeds were also stored hermeticallyat 15.9% moisture content at 40 °C for 0, 7, 14, 21 or 28d before transfer to 50 °C. This investigation showed thatthe standard deviation of the subsequent survival curves at50 °C was unaffected by the duration of previous storageat 40 °C. The results of both investigations were consistentwith the hypothesis that loss in probit viability is solelya function of the current storage environment, with no effectof change in temperature per se. The application of the viabilityequation to seed survival in fluctuating environments was validatedagainst independent observations for rice in uncontrolled storageconditions. Copyright 2001 Annals of Botany Company Temperature, seed storage, longevity, moisture content, viability equation, tomato, rice     

Characterization of the Stimulation of Ethylene Production by Galactose in Tomato (Lycopersicon esculentum Mill.) Fruit

We have characterized the stimulation of ethylene production by galactose in tomatoes (Lycopersicon esculentum Mill.). The effect of concentration was studied by infiltrating 0, 4, 40, 100, 200, 400, or 800 micrograms galactose for each gram of fresh fruit weight into mature green `Rutgers' fruit. Both 400 and 800 micrograms per gram fresh weight consistently stimulated a transient increase in ethylene approximately 25 hours after infiltration; the lower concentrations did not. Carbon dioxide evolution of fruit infiltrated with 400 to 800 micrograms per gram fresh weight was greater than that of lower concentrations. The ripening mutants, rin and nor, also showed the transient increase in ethylene and elevated CO₂ evolution by 400 micrograms per gram fresh weight galactose. 1-Aminocyclopropane-1-carboxylic acid (ACC) content and ACC-synthase activity increased concurrently with ethylene production. However, galactose did not stimulate ACC-synthase activity in vitro. The infiltrated galactose in pericarp tissue was rapidly metabolized, decreasing to endogenous levels within 50 hours. Infiltrated galacturonic acid, dulcitol, and mannose stimulated transient increases in ethylene production similar to that of galactose. The following sugars produced no response: sucrose, fructose, glucose, rhamnose, arabinose, xylose, raffinose, lactose, and sorbitol.     

串番茄果实货架期间与耐贮性有关的生理特性的变化

串番茄品种随着货架期延长,果实硬度、果肉硬度、原果胶含量逐渐下降;可溶性果胶含量逐渐上升;多聚半乳糖醛酸酶(PG)活性呈峰值变化,变化幅度小于普通番茄.     

Patterns of Assimilate Distribution and Source--sink Relationships in the Young Reproductive Tomato Plant (Lycopersicon esculentum Mill.)

Patterns of distribution of ¹⁴C were determined in 47-day-oldtomato plants (Lycopersicon esculentum Mill.) 24 h after theapplication of [¹⁴C]sucrose to individual source leaves fromleaves 1–10 (leaf 1 being the first leaf produced abovethe cotyledons). The first inflorescence of these plants wasbetween the ‘buds visible’ and the ‘firstanthesis’ stages of development. The predominant sink organs in these plants were the root system,the stem, the developing first inflorescence and the shoot ‘apex’(all tissues above node 10). The contribution made by individualsource leaves to the assimilate reaching these organs dependedupon the vertical position of the leaf on the main-stem axisand upon its position with respect to the phyllotactic arrangementof the leaves about this axis. The root system received assimilateprincipally from leaf 5 and higher leaves, and the stem apexfrom the four lowest leaves. The developing first inflorescencereceived assimilates mainly from leaves in the two orthostichiesadjacent to the radial position of the inflorescence on thevertical axis of the plant; these included leaves which weremajor contributors of ¹⁴C to the root system (leaves 6 and 8)and to the shoot apex (leaves 1 and 3). This pattern of distributionof assimilate may explain why root-restriction treatments andremoval of young leaves at the shoot apex can reduce the extentof flower bud abortion in the first inflorescence under conditionsof reduced photoassimilate availability. Lycopersicon esculentum Mill, tomato, assimilate distribution, source-sink relationships     

Chemical Control of Basal Stem Rot Disease of Tomato (Lycopersicon esculentum Mill.) in Northern Nigeria

Six fungicides (Aatopam-N, Aldrex T, Calixin M, PCNB, captan and captafol) were evaluated at 200 mg a.i.l^?1 for their effectiveness in reducing basal stem rot disease incited by Sclerotium rolfsii on tomato in pre- and post-inoculation soil drenches in the glasshouse. The results showed that only PCNB effectively reduced disease severity when applied to soil 10 days before inoculation. Of the two application methods only pre-inoculation soil drenching with the fungicides was efficacious in reducing disease severity. In field trials conducted in Samaru with Aldrex T, captan and PCNB, only PCNB was effective in combating the severity of the disease. It reduced the disease by about 88% in one trial.     

Effects of Ethylene on Photosynthesis and Partitioning in Tomato, Lycopersicon esculentum Mill

The extended period of ethylene release from ethephon (2-chloroethylphosphonicacid) after application to intact tomato plants has provideda model system in which the effects of ethylene on photosyntheticmetabolism and carbon partitioning has been studied. Ethylenerelease from leaf tissue after ethephon treatment was 10 timesgreater than that from untreated control leaves. The specificactivity of 14C2H4 released from [14C] ethephon remained constantover several days demonstrating that the ethylene was derivedfrom the applied ethephon. The ethephon-treated plants exhibitedextreme epinasty of the leaves and 24 h after application theflower buds in the first visible cluster had abscised, leafexpansion at the apex had ceased and developing adventitiousroots were visible on the lower stem. Rates of steady-state photosynthesis, respiration, photorespirationand transpiration were the same in treated and control leaves24 h after ethephon application. Both treated and control leavespartitioned similar proportions of newly-fixed 14C from 14CO²into neutral (46.4%), acidic (14.0%), basic (5.0%) and insoluble(34.0%) leaf fractions under steady-state conditions. The speedof 11C-assimilate movement in the stems of control plants (3.62±0.42cm min-1 towards the apex and 4.03±0.15 cm min-1 towardsthe roots) was more rapid than in the ethephon-treated plants(2.90±0.31 cm min-1 upwards and 2.59±0.22 cm min-1downwards). Furthermore, in the control plants 20.0±5.4%of the 14C exported to the plant from the source leaf was transportedtowards the developing flower cluster and young leaves. Twenty-fourhours after ethephon application only 6.5 ±1.7% of theexported 14C was translocated towards the shoot. Contrary tosome reports ethylene did not affect steady-state gas exchangeprocesses while carbon partitioning was significantly alteredindicating that ethylene effects on photosynthetic carbon metabolismare indirect and not due to direct effects on photosyntheticprocesses per se. Key words: Ethylene, photosynthesis, partitioning     

Cellular Growth in Roots of a Gibberellin-Deficient Mutant of Tomato (Lycopersicon esculentum Mill.) and its Wild-type

The role of gibberellins in regulating the growth of tomatoroots was investigated by comparing various cellular parametersin cultured roots of the gibberellin-deficient mutant gib-l/gib-lwith those in roots of the near-isogenic wild-type. In addition,wild-type roots treated with 0?1 µM 2S,3S paclobutrazol,an inhibitor of gibberellin biosynthesis, and mutant roots treatedwith 0?1 µM GA₃ were also compared: the former roots constitutea phenocopy of the mutant, whereas the latter roots appear tobe ‘normalized’ and similar to wild-type. The elongationof mutant and phenocopied roots were similar, their maximumelongation rates being about half or two-thirds that of wild-typeor GA₃-treated mutant roots, respectively. These rates wereinterpreted in terms of the numbers and lengths of cells withinthe meristematic and non-meristematic portions of the elongationzone. Mean meristem length tended to be shorter in both themutant and the 2S,3S paclobutrazol-treated wild-type roots thanin the other two types of root. A major difference between thetwo pairs of mutant and normal roots was their mean final celllengths: mean lengths of cortical cells of the mutant and 2S,3Spaclobutrazol-treated roots were, respectively, 39% and 25%shorter than the mean length of wild-type roots. Final celllength in the GA³-treated mutant roots were similar to wild-type.By contrast, the diameters of mature cortical cells of the mutantand phenocopy were about 20% greater than the diameters of equivalentwild-type or ‘normalized’ mutant cells. The meanvolumes of cortical cells in all four types of roots showedno significant differences. Knowledge of the distribution ofcortical cell lengths, widths and volumes along the root axis,together with information about the rate of root elongation,permitted comparisons of the relative elemental growth ratesof each of these three cellular parameters. The available evidence suggests that the level of endogenousgibberellins in mutant roots is lower than in wild-type roots.The present results, therefore, suggest that endogenous gibberellinsare necessary for normal growth of cultured tomato roots andthat they regulate the relative amounts of growth at the longitudinaland transverse walls of the cells which, in turn, affects theshape of the elongating cells. Key words: Cell growth, cultured roots, gibberellin, gib-l mutant, Lycopersicon esculentum, 2S,3S paclobutrazol, relative elemental growth rate, root meristem     

Identification and distribution of profilin in tomato (Lycopersicon esculentum Mill.)

Profilin is a G-actin monomer-binding protein which has been shown to participate in actin-based tipgrowth of animal cells. The abundance of profilin in pollen and its occurrence in several vegetable foods raises the question of the role of profilin in plants. First, its distribution throughout various parts of the plant needs to be determined. This paper describes observations on the presence of profilin in the tomato plant (Lycopersicon esculentum Mill.). The distribution of profilin in flower buds, stems, leaves, roots, and fruits of tomato was determined by immunoblotting and by tissue printing, showing that profilin is present in most if not all parts of the tomato plant.We gratefully acknowledge the help provided by Dr. A.T. Jagendorf and the donation of tomato seeds and maize pollen by N. Eanetta and Dr. M. Smith, respectively. The use of Dr. R. Wayne's SZH ILLD dissecting microscope is gratefully acknowledged. This work was aided by helpful discussions with C.S. Combs, Dr. C.A. Conley, and Dr. J. Andersland. This work was supported by a Hatch grant and NRI Competitive Grants Program/USDA 94-37304-1046 to MVP. This material is based upon work supported under a National Science Foundation Graduate Research Fellowship to DWD.     

Phosphorus use efficiency in anthocyanin-free tomato (Lycopersicon esculentum Mill.)

An anthocyanin-free tomato plant, H957, and its parental wild type, H883, were hydroponically grown to test for tolerance to a low phosphorus (P) in H957. The tolerance was evaluated by comparing growth and metabolism of H957 vs. H883 at different P concentrations ranging 25–400 μM. Fresh weights were measured weekly. Dry weight, mineral contents, photosynthetic rate, and P utilization ratios of the plants were measured after five weeks of growth in the hydroponic culture. Although the growth of both varieties was severely impaired at 25 μM P, H957 showed a greater fresh weight and dry weight at 50–400 μM P. H957 showed a higher net photosynthetic rate on older leaves while both varieties showed similar photosynthetic rate on young leaves. H957 tissue contains an overall lower P concentration in its tissue than H883. These observations together indicate that the anthocyaninless mutant H957 tolerate to lower P concentration. It does so by utilizing internal P with better efficiency rather than by absorbing external P better.