Potential Dry Matter and Water Import Rates in the Tomato Fruit in Relationship to Fruit Size

The tomato fruit was compared to a sphere with a radius R. Radialgrowth rates in the fruit (F_IW and F_ID) due to water importor to dry matter import, respectively, which are also the waterimport rate or dry matter import rate per unit surface areaof fruit, were calculated from two sets of published results.This data referred to fruits which swelled in such a way thatthe availability of assimilates had little effect on growth.Two varieties differentiated the two series of results and inone series, three trials were differentiated by the salinityof the nutrient solution. In all trials, it was found that F_IW and F_ID decreased whenR increased. Two phases were observed for F_IW: after a firstphase, F_IW decreased more quickly and almost linearly when Rincreased. F_ID was constant or decreased with respect to R.Except at the beginning of growth at the greatest salinity,there were clearly linear regressions between F_IW and F_ID suchas F_ID = aF_IW-b; where b was lower with higher salinity. Thechanges of the concentration of imported dry matter (F_ID/F_IWwere examined in terms of R and F_IW/R. The mechanisms controllingthe changes in F_IW and F_ID were discussed. The results suggestedfruit radius was an important parameter of these mechanisms.Thus, water import rate and dry matter import rate could eachbe considered to be the product of two factors: fruit surfacearea, which is directly dependent on fruit radius, and waterimport rate or dry matter import rate per unit of fruit surfacearea.Copyright 1993, 1999 Academic Press Dry matter, fruit growth, logistic model, sink size, tomato, water transfer     

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.     

A Simulation Model for Dry Matter Partitioning in Cucumber

A dynamic model is developed for the simulation of the dailydry matter distribution between the generative and vegetativeplant parts and the distribution among individual fruits ingreenhouse cucumber. The model is based on the hypothesis thatdry matter partitioning is regulated by the sink strengths ofthe plant organs. The sink strength of an organ is defined hereas its potential growth rate, i.e. the growth rate at non-limitingassimilate supply. The sink strength of each individual fruitis described as a function of its temperature sum after anthesisand the actual temperature, that of the vegetative plant partsas a function of actual temperature only. The formation rateof non-aborting fruits is essentially a function of the source/sinkratio. Model results agreed well with the measured fluctuating distributionof dry matter between fruits and vegetative parts. The measuredeffects of three intensities of fruit removal were also simulatedsatisfactorily. When simulating the partitioning among individualfruits the final fruit size was simulated quite well. However,the growth rate of young fruits was usually overestimated andthat of old fruits underestimated, because of dominance amongfruits. This phenomenon could be accounted for by incorporatingpriority functions into the model. Finally, a sensitivity analysisof the model was performed to investigate the effects of someclimatic factors, manipulations of the number of fruits on aplant and model parameters on dry matter distribution. Strategiesto manipulate the dry matter distribution are discussed.Copyright1994, 1999 Academic Press Cucumber, Cucumis sativus (L.), dry matter distribution, fruit growth, partitioning, simulation model, source-sink     

Water Import Rate in Tomato Fruit: A Resistance Model

A model of the water import rate in tomato fruit is proposed.It compares the fruit to a hollow sphere (P) with external radiusR and internal radius R_G, corresponding to pericarp, and containingan internal spherical part (G). The pathway limiting water inputrate at any point I at a distance r from the fruit centre wasassumed to be proportional: (a) in P, to the length of the arcwhich has a radius r and which goes from I to the pedicel extension;(b) in G, to r. The water input rate at I was modelled basedon a law similar to Darcy's law which takes into account thedifference between the water potential at entry of fruit andthe water potential at point I. This latter potential was thesum of fruit osmotic potential and pressure potential due toresistance of tissue to deformation. This potential was proportionalto R-r or R_G -r. The model was expressed at fruit level by alaw such that water mass imported per unit time per unit surfacearea of fruit (f_rw) was a linear function of R. The model wascompared to linear regressions of this rate in terms of R whichhad been found during fruit swelling from published results,and which were obtained at different values of nutrient solutionsalinity. The results suggested that water input in tomato fruitis conditioned by passive forces depending on fruit size.Copyright1994, 1999 Academic Press Fruit, growth, model, resistance, salinity, size, tomato, transfer, water     

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.     

Re-interpretation of an Experiment on the Role of Assimilated Transport Resistance in Partitioning in Tomato

The importance of transport resistance (distance between sourceand sink) on assimilate partitioning in tomato is questioned.Slack and Calvert ( Journal of Horticultural Science 52 : 309–315,1977) concluded that, in tomato, excising of fruit trusses showeda direct influence of distance from source on assimilate partitioning.A dry matter distribution model for tomato, based on the hypothesisthat distribution is regulated by the sink strengths of theplant organs and that no influence of transport resistance onpartitioning exists, has been described and validated by Heuvelink( Annals of Botany 77 : 71–80, 1996). Using this model,it is shown that the results of Slack and Calvert (1977) canbe explained more simply on the basis of the succession of trusseswith growth shifted with respect to time. Therefore, their resultsdo not prove that transport resistance plays a role in assimilatepartitioning. Allocation; distance; dry matter distribution; model; assimilate pool; partitioning; simulation; transport resistance; tomato     

Dry Matter Production in a Tomato Crop: Measurements and Simulation

Simulation of dry matter production by the explanatory glasshousecrop growth model SUKAM (Gijzen, 1992, Simulation Monographs),based on SUCROS87 (Spitters, Van Keulen and Van Kraalingen,1989, Simulation and systems management in crop protection),was validated for tomato. In the model, assimilation rates arecalculated separately for shaded and sunlit leaf area at differentcumulative leaf area in the canopy, taking into account thedifferent interception of direct and diffuse components of light.Daily crop gross assimilation rate (P_gd) is computed by integrationof these rates over total crop leaf area and over the day. Leafphotochemical efficiency and potential gross assimilation rateat saturating light depend on temperature and CO₂ concentrationand are approximated as being identical in the whole canopy.Crop growth results from P_gd minus maintenance respiration rate(R_m; dependent on temperature and crop dry weight), multipliedby the conversion efficiency (carbohydrates to structural drymatter; C_f). Growth experiments (periodic destructive harvest) with differentplanting dates and plant densities and two data-sets from commerciallygrown crops, were used for model validation. Hourly averagesfor global radiation outside the glasshouse, glasshouse temperatureand CO₂ concentration, together with measured leaf area index,dry matter distribution (for calculation of C_f) and organ dryweights (for calculation of R_m) were the inputs to the model. Dry matter production (both level and dynamic behaviour) wassimulated reasonably well for most experiments, but final drymatter production was under-estimated by about 27% for the commerciallygrown crops. At low irradiance and with large crop dry weight,growth rate was under-estimated, probably as a result of over-estimationof R_m. This could almost completely explain the large under-estimationfor the commercially grown crops, which had large dry weight.Final dry matter production was over-estimated by 7-11% if dailyaverages instead of hourly input of climatic data were used. It is concluded that SUKAM is a reliable model for simulatingdry matter production in a tomato crop, except for those situationswhere R_m has a large influence on crop growth rate (low irradianceand large crop dry weight). An improved estimate of R_m wouldtake into account the influence of metabolic activity. A preliminaryattempt to relate maintenance costs to relative growth rate(a measure for metabolic activity), showed promising results.Copyright1995, 1999 Academic Press Crop growth, dry matter production, glasshouse, maintenance respiration, metabolic activity, model, relative growth rate, respiration, simulation, tomato, model validation     

Regulation of the Partitioning of Dry Matter and Calcium in Cucumber in Relation to Fruit Growth and Salinity

The regulation of the partitioning of dry matter and calciumin relation to fruit growth was investigated in cucumber plantsgrown in the salinity range of 3-8 mS cm^-1 in NFT (NutrientFilm Culture), with or without a fruit pruning treatment. Thedry weight gain of the plants was proportional to the outdoorintegral irradiance, with a common daily rate of 1 g MJ^-1 m^-2in two crops grown under summer (18 MJ m^-2 d^-1) and autumn (7MJ m^-2 d^-1) conditions. Within the salinity range studied, thereduction of plant dry weight was 9% mS^-1 cm^-1. However, fruitdry weight was only reduced at salinities above 5·5 mScm^-1, although the daily dry matter accumulation by fruit, asa percentage of total dry matter accumulation, was increased.Salinity reduced the dry matter accumulation in the young shootproportionally more than in the fruit. Although the total plantCa content was reduced by 13% mS^-1 cm^-1, the Ca content of theyoung shoot was reduced by 16·6%, compared to 11% inthe fruit. Pruning fruit reduced neither plant dry weight norCa uptake. The growth of the remaining fruit, and to a lesserdegree of the young shoot, accounted for all surplus assimilates.Thus, fruit were the dominant sinks for assimilates whilst themature leaves were the strongest sinks for Ca. Nevertheless,the fruit sustained the capacity to import Ca better than theyoung shoot, when supplies of both assimilates and Ca were reducedby high salinity.Copyright 1994, 1999 Academic Press Cucumber, Cucumis sativus L., salinity, fruit pruning, dry matter and calcium     

Influence of Sink-Source Interaction on Dry Matter Production in Tomato

Sink-source ratio in tomato was manipulated, in six glasshouseexperiments, by fruit pruning (trusses pruned to two to sevenfruits immediately after fruit set of each truss), truss pruning(removal of every other truss at anthesis) and truss pruningin plants with two shoots. Periodic destructive harvest wereconducted for about 100 d after flowering of the first truss.Dry matter production was not influenced by sink-source ratio,whereas dry matter distribution between fruits and vegetativeparts was greatly affected. The fraction of dry matter distributedto the fruits at the end of the fruit pruning experiments (F_fruits)could be described accurately as a saturation-type functionof number of fruits retained per truss (N_f): F_fruits = 0.660(l-e^-0.341N_f). Specific leaf area and internode length decreasedand plant leaf area increased when sink-source ratio was reduced.Removal of every other truss at anthesis did reduce dry matterpartitioning into the fruits, but it did not influence internodelength. Plant development (number of visible leaves at the endof the experiments) was not influenced by sink-source ratio.In four experiments some plants were pruned to one fruit pertruss. Final dry matter production was 8-24% lower for theseplants, compared with plants with more than one fruit per truss.This was, at least party, the result of less light interceptionby these plants, which had strongly curled leaves pointing downwards. Results indicate that effects of sink demand on dry matter productionper unit of intercepted radiation and probably on leaf photosyntheticrate in commercial tomato production can be ignored.Copyright1995, 1999 Academic Press Dry matter production, feedback control, glasshouse, growth analysis, Lycopersicon esculentum, pruning, sink demand, sink-source ratio, tomato     

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     

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     

Diurnal Patterns of Transport and Accumulation of Minerals in Fruiting Plants of Lupinus angustifolius L.

Fluctuations in mineral elements id xylem (tracheal) sap, fruitphloem sap, leaflets and dmloping fruits were studied in a fieldpopulation of Lupinus angustifolius L. by three-hourly samplingover a 39 h period. Elements usually reached maximum contentsor concentrations at or near noon, minimum levels during thenight. Amplitudes of diurnal fluctuations in minerals lay withinthe range ±4–33 per cent of the mean content ofleaflets, and ±17–157 per cent of the mean concentrationsin xylem and phloem sap. Most minerals elements fluctuatcd inphase with daily changes in sugar level of phloem sap and drymatter and carbohydrate fluctuations of leaflets, suggestinga coupling of translocation of photosynthate and minerals fromthe leaflets. Rates of import of minerals by shoots wereestimatedfrom shoot transpiration and mineral concentrations in trachealsap. Average day time rates of import of most elements were12–25 times those at night. Translocation of minerals,nitrogen and carbon to fruits also exhibited diurnal periodicity,average rates of import king three to seven times higher inthe day than at night. A model of transport based on the carbonand water economy of the fruit suggested that P, K, Fe, Zn,Mn and Cu were imported predominantly by phloem. Estimates ofvascular import accounted for 87–104 per cent of the fruit'sactual increment of these elements. Na and Ca were gauged tobe imported mainly by xylem, Mg almost equally by xylem andphloem. However, large discrepancies existed for these threeelements between estimated vascular import and actual intakeby the fruit. Lupinus angustifolius L., mineral transport, accumulation, fruits, xylem sap, phloem sap, transpiration     

Evaluation of a Dynamic Simulation Model for Tomato Crop Growth and Development

A dynamic simulation model for tomato crop growth and development,TOMSIM, is evaluated. Potential crop growth and daily crop grossassimilation rate (P_gc,d) is computed by integration of leafassimilation rates over total crop leaf area throughout theday. Crop growth results fromP_gc,dminus maintenance respirationrate (R_m), multiplied by the conversion efficiency. Dry matterdistribution is simulated, based on the sink strength of theplant organs, which is quantified by their potential growthrate. Within the plant, individual fruit trusses and vegetativeunits (three leaves and stem internodes between two trusses)are distinguished. Sink strength of a truss or a vegetativeunit is described as a function of its developmental stage.In this paper, emphasis is on the interactions between the twosubmodels of, respectively, dry matter production and dry matterdistribution. Sensitivity analysis showed that global radiation,CO₂concentration, specific leaf area (SLA) and the developmentalstage of a vegetative unit at leaf pruning had a large influenceon crop growth rate, whereas temperature, number of fruits pertruss, sink strength of a vegetative unit and plant densitywere less important. Leaf area index (LAI) was very sensitiveto SLA and the developmental stage of a vegetative unit at leafpruning. Temperature did not influence the simulated R_m, asincreased respiration rate per unit of biomass at higher temperatureswas compensated by a decrease in biomass. The model was validatedfor four glasshouse experiments with plant density and fruitpruning treatments, and on data from two commercially growncrops. In general, measured and simulated crop growth ratesfrom 1 month after planting onwards agreed reasonably well,average overestimation being 12%. However, crop growth ratesin the first month after planting were overestimated by 52%on average. Final crop dry mass was overestimated by 0–31%,due to inaccurate simulation of LAI, resulting partly from inaccurateSLA prediction, which is especially important at low plant densityand in a young crop.Copyright 1999 Annals of Botany Company Crop growth, dry matter production, glasshouse, leaf area,Lycopersicon esculentum, partitioning, simulation model, tomato, TOMSIM.     

An Analysis of the Effects of Temperature and Light Integral on the Vegetative Growth of Pansy cv. Universal Violet (Violaxwittrockiana Gams.)

Pansies (Viola xwittrockiana Gams.) cv. Universal Violet weresown on five dates between Jul. and Dec. 1992 and placed insix temperature-controlled glasshouse compartments set to providemean temperatures between 6.5 and 30 °C. Shoot dry weightand leaf number were recorded. A model was constructed, to analysethe effects of light and temperature on dry matter accumulation,which assumed that relative growth rate (RGR) declined linearlywith thermal time accumulated from sowing, reflecting ontogeneticdrift. Furthermore, it assumed that RGR was a semi-ellipsoidfunction of temperature, rising to an optimum of 25.3 °Cand declining thereafter, and a positive linear function oflight integral. When fitted to data collected in this studythe model accounted for 94% of the variance in RGR. Independentvalidation using data from four further crops grown in glasshousecompartments at four different set point temperatures showedthat the model could also be used to predict plant dry weightaccurately (r ²=0.98). The rate of mainstem leaf productionwas also linearly related to both light integral and temperature. Pansy; Viola xwittrockiana ; temperature; light integral; dry weight; relative growth rate; leaf number     

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.     

Rates of Respiration and of Increase in Structural Dry Matter in Young Wheat, Ryegrass and Maize Plants in Relation to Temperature, to Water Stress and to Their Sugar Content

A method to determine the rate of conversion of reserve materialsinto structural dry matter in living, whole plants is presented.It is based on a brief measurement of plant respiration. Therate of increase in structural dry matter and of decrease ofreserve materials is calculated by subtracting the maintenancerespiration component from the total respiration. The remainder,the growth respiration rate, is multiplied by a factor thatis derived from the biochemical composition of the structuraldry matter formed. This method is applied to determine the relations of the rateof conversion of reserve material into structural dry matterto temperature, water stress and the level of reserve carbohydratesin plants of three species. The weakest part of the method is in the determination of therate of maintenance respiration. Consequences of different assumptionsconcerning the rate of adjustment of this respiration componentto modified environmental conditions are discussed. Lolium perenne L, Triticum aestivum L, Zea mays L, ryegrass, wheat, maize, respiration, maintenance respiration, water stress, sugar content, structured dry matter     

The Dynamics of Growth and Dry Matter Distribution in Cucumber

The dynamics of growth and proportional dry matter distributionbetween the vegetative parts and fruits of cucumber were studieddaily during a growing season. Most of the changes in dailyintegral of total solar radiation were reflected by changesin plant growth rate. Sometimes a time lag of a few days occurred,indicating the plants were adapting to radiation. The proportional dry matter distribution between fruits andvegetative parts showed a cyclic pattern. The daily proportionaldry matter distribution to the fruits varied between 40 and90% of the total dry matter. However, the cumulative dry weightof the fruits was fairly constant at 60% of the cumulative plantdry weight. The daily proportional dry matter distribution did not seemto be linked directly to the climate conditions (temperature,CO₂ concentration, relative humidity or daily light integral).The proportional distribution to the fruits showed a clear positivecorrelation with the fruit load (number and weight of fruits)on a plant. The number of fruits on a plant changed considerablyduring the growing season. This number was limited not by theformation of new fruits but by abortion of fruits within about10 d after flowering. The number of young fruits that did notabort appeared to correlate positively with the growth rateof the vegetative parts. Cucumis sativus (L.), cucumber, biomass allocation, partitioning, vegetative-generative growth, fruit growth, fruit abortion     

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.     

Prediction and Measurement of the Decline in the Critical-K, the Maximum-K and Total Cation Plant Concentrations during the Growth of Field Vegetable Crops

The declines in maximum and critical K concentrations in plantdry matter of 16 different vegetable species were predictedfrom emergence to maturity by assuming that both were proportionalto the critical %N calculated in terms of plant dry matter perunit area using previously-described equations. Values of theproportionality constants were obtained from published measurementsmade, at commercial maturity, of crops grown in multi-levelfertilizer experiments. Predictions were tested: (a) againstmeasurements made at intervals during growth in experimentsreceiving a single level of fertilizer; (b) against measurementsmade of the highest K concentrations measured at the seedlingstage in soil-K gradient experiments; and (c) against the resultsof a K-fertilizer-response experiment in which harvests werecarried out at intervals during growth. Results were consistentwith the predictions and, thus, with the view that both criticaland maximum K concentrations are proportional to critical %Nthroughout growth. K concentrations in plant tissue water fluctuatedwidely during the growing season and values, averaged over theentire growing period for each of ten crops, varied by a factorof 3. These values were proportional to the mean cation concentrations(meq l^-1) calculated by assuming that all the ions were in solution.Total cation concentration (meq 100 g^-1) of dry matter was linearlyrelated to critical N concentration. Evidence was also obtainedthat maximum K concentration, critical K concentration and totalcation concentration (meq 100 g^-1) during growth were linearlyrelated to relative growth rate, provided that crop weightswere greater than 2 t ha^-1dry matter. A hypothesis was developedto co-ordinate these findings.Copyright 1998 Annals of BotanyCompany. Vegetable crops, cation, plant potassium, plant nitrogen, critical concentration, relative growth rate, plant weight.     

Water relations of the tomato during fruit growth

Fruit and stem water potentials of tomato plants were measured continuously for several days using automated psychrometers. A linear voltage displacement transducer was used to simultaneously measure diameter changes on an adjacent fruit. A strong correlation was observed between the water potential gradient of the fruit and stem, and changes in fruit diameter. Fruit diameter increased when the apoplasmic water potential gradient favoured solution flow into the fruit and fruit shrinkage occurred only when the water potential gradient was inverted. Based on our data and other published data (Ehret & Ho 1986; Lee 1989a) on phloem transport in tomato, we have concluded that low stem water potentials have an immediate and direct effect on phloem turgor; reducing the driving force for sap flow into the fruit. Since fruit water potential remained relatively constant, the diurnal variation in stem water potential was sufficient to account for the correlation with changes in fruit diameter. There are consequences with respect to predicting the accumulation of dry matter in tomato fruit.