水分和盐分胁迫对番茄植株生长和木质部水力特性的影响

木质部是植株体内水分传输的主要通路,其水力特性的变化会影响植株的水分关系和果实的水分积累。目前关于番茄植株木质部解剖结构和水力特性对水分和盐分胁迫的响应及其与植株生长和果实含水量之间的关系尚不明确。本研究通过日光温室番茄盆栽试验,设置3个处理:对照,土壤含水量(θ)为75%～95%田间持水量(FC),初始电导率(EC)为0.398 dS·m^-1;水分胁迫,开花前θ为75%～95% FC,开花后至成熟期θ为45%～65% FC,EC为0.398 dS·m^-1;盐分胁迫,θ为75%～95% FC,EC为1.680 dS·m^-1,研究了樱桃型番茄(红宝石)和中果型番茄(北番501)植株在水分和盐分胁迫下的植株生长、果实含水量以及木质部水力特性的变化。结果表明: 与对照相比,水分和盐分胁迫下茎秆横截面积和木质部导管直径分别减小了22.0%～40.7%和10.0%～18.3%,茎秆比导水率和桁架柄比导水率分别降低了8.8%～41.1%和12.9%～28.4%,抑制了植株生长,减少了地上部鲜重、果实大小、果实鲜重和含水量,且与樱桃型番茄相比,中果型番茄的降幅更大。此外,果实含水量分别与茎秆和桁架柄比导水率呈显著正相关。综上,番茄植株在水分和盐分胁迫下木质部水力特性指标减小,生长被抑制,果实鲜重显著降低,最终导致产量降低。其中,中果型番茄相较于樱桃型番茄对水分和盐分胁迫更敏感。     

Expansion rate of young tomato fruit growing on plants at positive water potential

Changes in tomato fruit expansion rate and carbohydrate content have been assessed during treatments designed to alter the carbon import rate. Because fruit expansion is sensitive to plant water status, the relationship with carbon import is difficult to assess, and thus, the diameter growth rate of young fruit was measured on plants maintained at positive water potentials. The detached top metre of a tomato plant was supplied with water, through the cut stem base, at a pressure of 0.08 MPa. Developing fruit on the stem continued to grow at high rates for up to 2 d. Fruit diameter growth rate after plant detachment was directly proportional to temperature. Plants acclimated to different continuous irradiances for 5 d before detachment gave fruit growth rates after plant detachment which were directly proportional to the irradiance up to 7 MJ m⁻²d⁻¹ photosynthetically active radiation (PAR). In continuous darkness, fruit growth rate remained unchanged for 20 h and then declined to less than 40% of the original rate over the following 30 h. On re-exposure to light, about 5 h elapsed before fruit growth rate increased but the growth rate stabilized at approximately 50% of the rate in continuously illuminated plants. During darkness, both fruit starch and hexose content decreased in comparison to illuminated controls, but on re-illumination, carbohydrate content increased before carbon was allocated to structural growth. Heat-killing the phloem of the fruit pedicel caused an immediate, but temporary, cessation of growth. After a partial recovery, expansion growth continued, but more slowly than in untreated fruit and at steadily declining rates. Starch and hexose sugars were not used to provide substrates for growth and starch synthesis was maintained. Continuing cell expansion was assumed to have been supported by water import via the xylem. Thus, fruit expansion may be related to carbon accumulation in most circumstances, but the changing allocation of imported carbon to storage and cell expansion may modify this relationship.     

A fruit-specific phosphoenolpyruvate carboxylase is related to rapid growth of tomato fruit

Malic and citric acids accumulate in cherry tomato (Lycopersicon esculentum Mill.) fruit during the period of rapid growth, from the end of cell division to the onset of ripening. The involvement of phospho enolpyruvate carboxylase (PEPCase, EC 4.1.1.31) in organic acid accumulation and tomato fruit development was investigated. Two PEPCases, named LYCes;Ppc1 and LYCes;Ppc2 and mapped to chromosomes 12 and 7, respectively, were shown to be differentially expressed during tomato fruit development. LYCes;Ppc1 mRNA was present in all fruit tissues and in all other plant organs examined. In contrast, LYCes;Ppc2 was strongly and specifically expressed in fruit from the end of cell division to ripening. No LYCes;Ppc2 expression was detected by northern blot in other plant tissues. In fruit, the increase in LYCes;Ppc2 mRNA was closely followed by an increase in fruit PEPCase protein and activity, and was coincident with the increased accumulation of malate and citrate during the initial period of rapid growth rate, from 8 to 20 days post anthesis. Localization of LYCes;Ppc2 mRNA in young tomato fruit by in situ hybridization revealed that LYCes;Ppc2 is preferentially expressed in large cells of the pericarp and in enlarging cells of the gel surrounding the seeds. Examination of the kinetic and regulatory properties of the PEPCases of growing and ripening fruit further showed that PEPCase in growing fruit is less sensitive to low pH and malate inhibition, indicating a high phosphorylation state and/or the presence of a PEPCase isoform with these characteristics. Taken together, these results indicate that in developing tomato fruit PEPCase is probably important in permitting the synthesis of organic acids to provide the turgor pressure necessary for cell expansion.     

Respiration and growth of tomato fruit

The respiration rate and diameter expansion growth of young tomato fruit were measured simultaneously and related to changes in carbon import and plant water status. Respiration rate was directly proportional to the volume expansion rate of fruit growing on isolated plant tops at a positive water potential, whether the growth rate was changed by changing the fruit temperature or by manipulating the source:sink ratio of the plants. From the latter relationship, the maintenance respiration rate was estimated by extrapolation to zero growth and was found to be about 25% of the respiration rate of the average fruit at 21°C. Alternatively, when carbon import was prevented by heat-ringing the fruit peduncle, the respiration rate of the fruit declined to about 40% of the control rate and remained steady, while the expansion rate then declined steadily to >10% of the control rate. These results show that fruit expansion was not contributing significantly to fruit respiration. Indeed, large fluctuations in fruit expansion rate could also be induced by repeated darkening and illumination of potted plants without a corresponding change in fruit respiration. Most significantly, fruit expansion was considerably reduced when plants were allowed to wilt, hut there was no change in fruit respiration rate unless the fruit peduncle was subsequently heat-ringed. We conclude that a major part of the respiration of young tomato fruit was determined by the rate of carbon import, or associated processes, and that fruit expansion per se can occur with relatively low respiratory costs.     

Identification of growth processes involved in QTLs for tomato fruit size and composition

Many quantitative trait loci (QTLs) for quality traits havebeen located on the tomato genetic map, but introgression offavourable wild alleles into large fruited species is hamperedby co-localizations of QTLs with antagonist effects. The aimof this study was to assess the growth processes controlledby the main QTLs for fruit size and composition. Four nearlyisogenic lines (NILs) derived from an intraspecific cross betweena tasty cherry tomato (Cervil) and a normal-tasting large fruittomato (Levovil) were studied. The lines carried one (L2, L4,and L9) or five (Lx) introgressions from Cervil on chromosomes1, 2, 4, and 9. QTLs for fruit size could be mainly associatedwith cell division processes in L2 and L9, whereas cell expansionwas rather homogeneous among the genotypes, except Cervil forwhich the low expansion rate was attributed to low cell plasticity.The link between endoreduplication and fruit size remained unclear,as cell or fruit sizes were positively correlated with the cellDNA content, but not with the endoreduplication factor. QTLsfor fruit composition reflected differences in water accumulationrather than in sugar accumulation, except in L9 for which theup-regulation of sucrose unloading and hexose transport and/orstarch synthesis was suggested. This may explain the increasedamount of carbon allocated to cell structures in L9, which couldbe related to a QTL for fruit texture. In Lx, these effectswere attenuated, except on fruit size and cell division. Finally,the region on top of chromosome 9 may control size and compositionattributes in tomato, by a combination of QTL effects on celldivision, cell wall synthesis, and carbon import and metabolism. Key words: Cell division and expansion, endoreduplication, fruit quality, near isogenic line, osmotic regulation, quantitative trait locus, Solanum lycopersicum, starch, sugar and acid contents Received 22 July 2008; Revised 17 October 2008 Accepted 20 October 2008     

Non-hydraulic regulation of fruit growth in tomato plants (Lycopersicon esculentum cv. Solairo) growing in drying soil

Tomato (Lycopersicon esculentum cv. Solairo) fruit growth, fruit mesocarp and leaf epidermal cell turgor, and fruit and leaf sub-epidermal apoplastic pH were monitored as plants were allowed to dry the soil in which they were rooted. Soil drying regimes involved splitting the root system of plants between two halves of a single pot separated by a solid impervious membrane to form a split-root system. Plants were then allowed to dry the soil in both halves of the pot (a soil-drying (SD) treatment) or water was supplied to one-half of the pot (a partial root-drying (PRD) treatment), allowing only one-half of the root system to dry the soil. A well-watered control treatment watered the soil on both halves of the pot. The rate of fruit growth was highly correlated with the soil water content of both sides of the SD treatment and the dry side of the PRD treatment. Soil drying caused a significant restriction in fruit growth rate, which was independent of any changes in the turgor of expanding fruit mesocarp cells in the PRD treatment. By supplying water to half of the root system, the turgors of mesocarp cells were maintained at values above those recorded in well-watered controls. The turgor of leaf epidermal cells exhibited a similar response. The pH of the sub-epidermal apoplastic compartment in leaves and fruit increased with soil drying. The dynamics of this increase in leaves and fruit were identical, suggesting free transport of this signal from shoot to fruit. Fruit growth rate and sub-epidermal pH within the fruit showed a strong correlation. The similarity of fruit growth response in the SD and PRD treatment, suggests that tomato plants respond to a discrete measure of soil water status and do not integrate measures to determine total soil water availability. The results of this study are not consistent with Lockhartian models of growth regulation in expanding fruit of a higher plant. A non-hydraulic, chemical-based signalling control of fruit growth in plants growing in drying soil is proposed.     

Depression of sink activity precedes the inhibition of biomass production in tomato plants subjected to potassium deficiency stress

Tomato [Solanum lycopersicum (formerly Lycopersicon esculentum) L. cv. Momotarou] plants were grown hydroponically inside the greenhouse of Hiroshima University, Japan. The adverse effects of potassium (K) deficiency stress on the source-sink relationship during the early reproductive period was examined by withdrawing K from the rooting medium for a period of 21 d. Fruits and stem were the major sink organs for the carbon assimilates from the source. A simple non-destructive micro-morphometric technique was used to measure growth of these organs. The effect of K deficiency was studied on the apparent photosynthesis (source activity), leaf area, partitioning (13)C, sugar concentration, K content, and fruit and stem diameters of the plant. Compared with the control, K deficiency treatment severely decreased biomass of all organs. The treatment also depressed leaf photosynthesis and transport of (13)C assimilates, but the impact of stress on these activities became evident only after fruit and stem diameter expansions were down-regulated. These results suggested that K deficiency diminished sink activity in tomato plants prior to its effect on the source activity because of a direct effect on the water status of the former. The lack of demand in growth led to the accumulation of sugars in leaves and concomitant fall in photosynthetic activity. Since accumulation of K and sugars in the fruit was not affected, low K levels of the growing medium might not have affected the fruit quality. The micro-morphometric technique can be used as a reliable tool for monitoring K deficiency during fruiting of tomato. K deficiency directly hindered assimilate partitioning, and the symptoms were considered more detrimental compared with P deficiency.     

Sugar uptake by protoplasts isolated from tomato fruit tissues during various stages of fruit growth

The uptake of radioactive glucose and sucrose by protoplasts isolated from pericarp and placenta tissues of tomato ( Lycopersicon esculentum cv. Counter) fruit was investigated in relation to the dry matter accumulation rates of these tissues. Uptake of glucose by protoplasts isolated from pericarp tissue was highest in fruit of around 20 g fresh weight or 25 days after anthesis. Sucrose uptake by pericarp protoplasts was lower than that of glucose and did not show a peak of uptake. The maximum rate of glucose uptake by protoplasts from the pericarp was at the time when the tomato fruit was accumulating dry matter at the highest rate. Glucose uptake by placenta protoplasts was lower and at a similar level as sucrose.
Protoplast uptake of glucose, but not of sucrose, was partially inhibited by (1) p -chloromercuribenzene sulphonic acid, a sulphydryl group modifier; (2) erythrosin B, an H⁺-ATPase inhibitor; and (3) valinomycin, a K⁺-ionophore, suggesting that membrane transport of glucose by tomato fruit sink cells may be a carrier-mediated, energy-dependent process.
The main route of carbohydrate accumulation by tomato fruit during the period of rapid fruit growth may be by cleavage of sucrose by apoplastic acid invertase prior to hexose transport across the plasma membrane.     

Modulation of Competition between Fruits and Leaves by Flower Pruning and Water Fogging, and Consequences on Tomato Leaf and Fruit Growth

The effects of water fogging and reducing plant fruit load werestudied in a tomato crop grown in a glasshouse under Mediterraneansummer conditions. The objective of these treatments was toreduce competition between leaves and fruits for carbohydratesand water. Flower pruning increased plant leaf area and increasedfruit, stem, lamina and petiole dry mass (DM). This indicatesthat leaf area growth was limited during the summer due to competitionbetween fruits and leaves for assimilates. In contrast, reducingthe air vapour pressure deficit (VPD) by water fogging had noeffect on plant leaf area or aerial plant DM. Interestingly,there was a significant interaction between plant fruit loadand VPD: the higher the leaf[ratio]fruit ratio the greater theresponses to a reduction in VPD (increase in fruit DM, fruitdiameter, fruit and leaf expansion rate). The data suggest thatunder high fruit loads, water and carbohydrates limit growthunder Mediterranean summer conditions. However, reducing VPDwas not always sufficient to enhance fruit and leaf growth.This might be due to the lower leaf area under high fruit load.In contrast, reducing VPD under low fruit load triggered higherrates of leaf and fruit expansion; this is probably linked toa greater availability of water and carbohydrates. Copyright2001 Annals of Botany Company Assimilate competition, assimilate supply, flower pruning, fruit load, fruit growth, generative/vegetative growth, leaf growth, Lycopersicon esculentum, specific leaf weight, tomato, vapour pressure deficit, water stress     

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     

The effect of nitrogen and phosphorus deficiency on flavonol accumulation in plant tissues

The flavonol content of Arabidopsis thaliana and tomato seedlings was assessed in conditions of reduced nitrogen or phosphorus availability. In both systems, a significant inverse relationship was observed between nutrient availability and flavonol accumulation, with nitrogen limitation promoting the greatest increase in flavonols. A trial was established to determine the effects of decreased nitrogen and phosphorus availability on the flavonol content of leaf and fruit tissues of tomato plants (Lycopersicon esculentum cv. Chaser) in a commercial situation. Nutrients were supplied by a hydroponic system with nutrient regimes designed to provide the highest and lowest nitrogen and phosphorus levels with which it is possible to support plant growth and fruit set. Fruiting was abundant and tomato fruits were harvested at mature green, breaker and red stages of ripening; leaves were also harvested from the tops of the plants. All tissues were analysed for flavonol content using reversed‐phase high‐performance liquid chromatography. Flavonol accumulation in the leaves of mature tomato plants was found to increase significantly in response to nitrogen stress, whereas phosphorus deficiency did not elicit this response. Reduced nitrogen availability had no consistent effect on the flavonol content of tomato fruits. Phosphorus deficiency elicited an increase in flavonol content in early stages of ripening. Effects of nutrient stress on the flavonol content of tomato fruits were lost as ripening progressed. The findings suggest that nutrient status may be employed to manipulate the flavonol content of vegetative tissues but cannot be used to elevate the flavonol content of tomato fruit.     

The effect of assimilate supply on fruit growth and hormone levels in tomato plants

Rates of dry matter accumulation and contents of starch, sugars and abscisic acid (ABA) of tomato fruits differed significantly during development at three positions (proximal, middle and distal) on a truss. Proximal fruits, which accumulated dry matter most rapidly during early development, generally had least ABA (per g DW).Partial defoliation reduced carbon accumulation by all fruits but increased ABA, especially in distal fruit, and indoleacetic acid (IAA), particularly in proximal fruits. The ABA content of leaves in partially defoliated plants was similar to that of leaves on non-defoliated plants.Removal of distal fruits on a truss enhanced carbon movement to the remaining proximal fruits and also increased their ABA content early in development but did not affect their IAA content. On the other hand, when proximal fruit were removed there was no large or lasting increased accumulation of carbon by the remaining distal fruits and they contained less ABA and IAA than fruits on plants without fruit thinning. Leaf carbon and ABA levels showed no marked trend in response to fruit thinning.The amount of carbon in the stems was increased by fruit thinning but decreased by partial defoliation.The possible roles of ABA and IAA in regulating fruit growth are discussed.Part of this work has been presented to a Symposium on Phloem loading and related processes at Bad Grund/Oberhar, W. Germany, July 1979.     

How do salinity and water stress affect transport of water,assimilates and ions to tomato fruits?

The study was conducted in order to determine whether water stress affects the accumulation of dry matter in tomato fruits similarly to salinity, and whether the increase in fruit dry matter content is solely a result of the decrease in water content. Although the rate of water transport to tomato fruits decreased throughout the entire season in saline water irrigated plants, accumulation rates of dry matter increased significantly. Phloem water transport contributed 80–85% of the total water transport in the control and water-stressed plants, and over 90% under salinity. The concentration of organic compounds in the phloem sap was increased by 40% by salinity. The rate of ions transported via the xylem was also significantly increased by salinity, but their contribution to fruit osmotic adjustment was less. The rate of fruit transpiration was also markedly reduced by salinity. Water stress also decreased the rate of water transport to the tomato fruit and increased the rate of dry matter accumulation, but much less than salinity. The similar changes, 10–15%, indicate that the rise in dry matter accumulation was a result of the decrease in water transport. Other parameters such as fruit transpiration rates, phloem and xylem sap concentration, relative transport via phloem and xylem, solutes contributing to osmotic adjustment of fruits and leaves, were only slightly affected by water stress. The smaller response of these parameters to water stress as compared to salinity could not be attributed to milder stress intensity, as leaf water potential was found to be more negative. Measuring fruit growth of girdled trusses, in which phloem flow was inactive, and comparing it with ungirdled trusses validated the mechanistic model. The relative transport of girdled as compared to ungirdled fruits resembled the calculated values of xylem transport.     

Light regulation of sink metabolism in tomato fruit : I. Growth and sugar accumulation

Light/dark effects on growth and sugar accumulation in tomato (Lycopersicon esculentum) fruit during early development were studied on intact plants (in vivo) and in tissue culture (in vitro). Through the use of an in vitro culture of tomato fruit, it was possible to investigate the direct effects of light on sink metabolism by eliminating the source tissue. Similar growth patterns were found in vivo and in vitro. Fruit growth in different sugars indicated that sucrose was the best source of carbon for in vitro fruit growth. Fruit growth increased as sucrose concentration increased up to 8%. Darkening the fruit decreased fruit dry weight about 40% in vivo and in vitro. The differences in the CO₂ exchange rate between light and dark grown fruit indicated that light stimulation of fruit growth was due to mechanisms other than photosynthesis. Supporting this conclusion was the fact that light intensities ranging from 40 to 160 micromoles per square meter per second had no significant influence on fruit growth, and light did not increase growth of fruit cultured with glucose or fructose as a carbon source. However, light stimulated fruit growth significantly when sucrose was used as the carbon source. Light-grown fruit took up 30% more sucrose from the same source and accumulated almost twice as much hexose and starch as dark-grown fruit. A possible expansion of an additional sink for carbon by light stimulation of starch synthesis during early development will be discussed.     

An analysis of the accumulation of water and dry matter in tomato fruit

Abstract Previously published data from tomato plants grown in nutrient solutions having one of three electrical conductivities (2, 12 and 17 mS cm^?1) were analysed. The rate of water import into the fruit, and the proportion of this conducted by the xylem stream were calculated from the daily rates of transpiration and the net accumulation of water and calcium. The rate of water import decreased as the conductivity of the nutrient solution rose, the maximum daily import rates in the third week after pollination being 3.2, 3.0 and 1.8 g fruit^?1 d^?1 for fruit grown at 2, 12 and 17 mS cm^?1, respectively. During fruit development, the proportion of water imported via the xylem fell from 8–15% to 1–2% at maturity. The principal source of water for tomato fruit growth was phloem sap. Based on the daily rates of net dry matter accumulation, respiration and phloem water import, the calculated dry matter concentration of the phloem sap declined from 7 to 3%, or from 12.5 to 7.8% during fruit development in low or high salinity, respectively. The similar dry matter accumulation of fruit grown at different salinities was due to changes in both volume and concentration of phloem sap. Potassium salts in tomato fruit were calculated lo have contributed –0.29, –0.48 and –0.58 MPa to total fruit osmotic potential in the 2, 12 and 17 mS cm^?1 treatments, respectively, which accounted for 38% or 49% of the measured total osmotic potential of the 2 mS cm^?1 or 17 mS cm^?1 treatments. The contribution of hexoses to total fruit osmotic potential in the young fruit was from about –0.1 to –0.2 MPa at all salinities. The osmotic potential of tomato fruit is regulated more by potassium salts than by hexoses.     

Role of transpiration from fruits in phloem transport and fruit growth in tomato fruits

Sink activity of fruits had been suggested to vary depending on transpiration of fruits. In this study, the effect of transpiration on dry matter accumulation was evaluated in tomato ( Lycopersicon esculentum Mill.). Fruits of cv. Saturn at 14 days after anthesis were enclosed in chambers and aerated with dried (<15% RH) or moistened (>90% RH) air. These treatments did not cause any significant differences in fruit fresh weight, dry weight, percentage of dry matter, and concentration of soluble sugars within 5 days of the treatment, or the import of ¹⁴C within 18 h after the application of ¹⁴CO₂ to the source leaves. However, displacement transducer measurement of each fruit showed a 40% reduction in growth rate in response to exchange of moistened air with dried air. When fruits of cv. Momotaro were exposed to transpiration treatments from the beginning of visible fruit enlargement until the ripening stage, the fruits exhibited 20% reduction in growth and lower accumulation of dry matter at harvest following treatment with dried air. These results suggested that higher transpiration reduced both water accumulation and dry matter accumulation. In contrast, when fruit growth was mechanically restricted by enclosing the fruits in a chamber packed with glass beads, and dried or moistened air was passed through the spaces between the glass beads, fruits exhibited higher dry matter accumulation under dried air treatment conditions. The results show that only under artificial conditions would transpiration of fruits potentially drive carbohydrate transport; it does not serve as a limiting step of carbohydrate transport to tomato fruits under normal circumstances.     

Dry Matter and Water Import Rates in the Tomato Fruit: a Model Incorporating the Changes in Sap Viscosity and Osmotic Potential with Temperature

The change in water import rate in tomato fruit was modelledby incorporating into a previously-published model the changesin sap viscosity and osmotic potential into fruit with temperature.An experimental relationship between water and dry matter importrates was used to compare the model to dry matter import ratesin fruit measured by Walker and Thornley (Annals of Botany 41:977-985, 1997) at different temperatures. The effect of temperatureon the water import rate, calculated from the model, was alsocompared with the effect of temperature on the fruit growthrate measured by Pearce, Grange and Hardwick (Journal of HorticulturalScience 68: 1-11 and 13-23, 1993). The model accounted for alarge part of these temperature effects. It was concluded that resistances in sap transfer pathways inthe tomato fruit could be due to viscosity. These results supported,on the one hand, the hypothesis that the progressive decreaseof water import rate during fruit growth could result partlyfrom the progressive increase in transfer pathway length, and,on the other hand, the hypothesis that the ratio between waterand dry matter import rates could depend on flow conditionsin transfer pathways. The equations of the model could be usedto simulate tomato fruit growth, mass and dry matter contentin relation to fruit size, to nutrient solution salinity andto fruit temperature.Copyright 1995, 1999 Academic Press Dry matter, fruit, growth, model, resistance, sap, temperature, tomato, transfer, viscosity, water     

UV-B辐射增强和CO2浓度倍增的复合作用对番茄生长和果实品质的影响

以番茄（Lycopersicon esculeutum）为研究对象,在人工模拟8.40 kJ·m^-2的UV-B辐射和700 μmol·mol^-1的CO₂浓度复合处理下,研究了番茄的生长和果实品质变化.结果表明,UV-B辐射使番茄的株高、鲜重、干重、总叶绿素、叶绿素a、叶绿素b、光合速率、水分利用效率、可溶性蛋白、维生素c及番茄红素等降低,导致果实品质恶化;而CO₂浓度倍增作用相反.在UV-B辐射增强和CO₂浓度倍增复合作用下,番茄的上述指标与对照相比差异不明显.分析认为,CO₂倍增与UV-B辐射增强复合处理下,CO₂的正效应作用可以减轻甚至抵消UV-B辐射的负效应.     

Pectin Methylesterase Isoforms in Tomato (Lycopersicon esculentum) Tissues (Effects of Expression of a Pectin Methylesterase Antisense Gene)

We have identified two major groups of pectin methylesterase (PME, EC 3.1.1.11) isoforms in various tissues of tomatoes (Lycopersicon esculentum). These two groups exhibited differential immuno-cross-reactivity with polyclonal antibodies raised against tomato fruit PME or flax callus PME and differences in their accumulation patterns in tissues of wild-type and transgenic tomato plants expressing a PME antisense gene. The group I isoforms with isoelectric points (pls) of 8.2, 8.4, and 8.5 are specific to fruit tissue, where they are the major forms of PME activity. The group II PME isoforms, with pl values of 9 and above, are observed in both vegetative and fruit tissues. The group I isoforms cross-react with polyclonal antibodies raised to a PME isoform purified from fruit, whereas the group II isoforms cross-react with antibodies to a PME purified from flax callus. Expression of a fruit-specific PME anti-sense gene impairs accumulation of the group I PME isoforms, with no apparent effect on the accumulation of the group II PME isoforms. The absence of any noticeable effects on growth and development of transgenic plants suggests that the group I PME isoforms are not involved in plant growth and development and may play a role under special circumstances such as cell separation during fruit ripening.