LEAF DEVELOPMENT IN THE NORMAL AND SOLANIFOLIA MUTANT OF TOMATO (LYCOPERSICON ESCULENTUM)

Leaf development in the normal (lobed margin) and the solanifolia (sf/sf) mutant (entire margin) of tomato (Lycopersicon esculentum) was compared at the light and scanning electron microscope levels. The shoot apices of the mutant plants contained microbodies near the axil of the youngest leaf, which were absent in the normal plants. The structural and morphological events in the initiation of leaf primordia were similar in the two genotypes. The pattern of leaflet emergence was also similar in the two types of plants, but the timing of leaflet production was different. The first pair of leaflet primordia in the normal plants was produced on P₃, whereas in the mutant it was not produced until P₅. The adult leaves of sf/sf plants were larger than those of normal, and the greater leaf area in the mutant was associated with a greater adaxial epidermal cell and areole area. A continuous marginal fimbriate vein (MFV) was present along the margin of each of the normal leaflets. However, a continuous MFV was absent in the mutant leaflets. It is suggested that the absence of a continuous MFV in the mutant might alter the nutritional and hormonal supply to the leaf margin, which ultimately leads to a modified leaf, i.e., with an entire margin.     

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     

Effects of Gibberellin on Shoot Development in the dgt Mutant of Tomato

The morphological effects of gibberellin A₃ (GA₃) on the dgtmutant of tomato were investigated. The mutant effectively showedthe normal range of responses, including a promotion of stemlength due to an increased number of longer internodes, a dramaticincrease in apical dominance, and effects on leaf shape andcolour. In the case of stem elongation, the quantitative responseof the mutant was greater than normal. The morphological abnormalitiescharacteristic of the dgt mutant, such as horizontal growth,a thin stem and hyponastic leaves, were not normalized by GA₃. It is concluded that the demonstrated lack of response to auxinof the dgt mutant does not impair its gibberellin responses. Tomato, gibberellin, auxin, mutant, shoot development     

Gibberellins and the Growth of Excised Tomato Roots: Comparison of gib-1 Mutant and Wild Type and Responses to Applied GA3 and 2S, 3S Paclobutrazol

Clones of excised roots of wild type tomato (Lycopersicon esculentum,Mill., cv. Moneymaker) and a near-isogenic GA-deficient mutant(gib-1/gib-1) were cultured in modified White's medium containing1.5% w/v sucrose. The linear elongation rate of the main axisof the gib-1 mutant was 40% less than that of the wild type.In addition, the main axis of the gib-1 mutant was thicker thanthat of the wild type but main axis volume growth was the samein both genotypes, indicating that the gib-1 allele was affectingthe orientation of root expansion. There was no evidence tosuggest that the gib-1 allele affected either the pattern ofemergence or the density of lateral roots. Elongation rate andthickness of gib-1 mutant roots were restored to those of thewild type by the addition of low concentrations (0.1–1.0µM) of gibberellic acid (GA3). These concentrations ofGA3 caused a slight reduction in extension growth of wild typeroots, indicating that endogenous GAs were not limiting elongationof normal roots in culture. The GA biosynthesis inhibitor, 2S,3S paclobutrazol, at 0.1 µM, significantly reduced elongationof wild type roots and this inhibition was counteracted by 0.1µM GA₃. It is concluded that the difference in growthbetween the gib-1 mutant and the wild type represented GA-dependentgrowth. Low concentrations of 2S, 3S paclobutrazol caused onlya small (5%) reduction in growth of the gib-1 mutant and thisgrowth inhibition was not reversed by GA₃. This observation,and the fact that gib-1 mutant roots grow in the absence ofadded GA₃, suggested that part of root growth was GA-independent.However, the possibilities that the gib-1 mutant is ‘leaky’and that paclobutrazol does not inhibit GA biosynthesis completelycannot be excluded. Key words: gib-1 mutant, gibberellic acid, Lycopersicon esculentum, 2S, 3S paclobutrazol, root growth     

Development of the Fifth Leaf is Indicative for Whole Plant Performance at Low Temperature in Tomato

In the search for early-detectable selection criteria for growthat low temperature conditions in tomato, first the initiationand growth of individual leaves was analysed. Scanning electronmicroscopy revealed that the first four primordia had alreadydeveloped during the germination period at 25°C. The primordiumof the fifth leaf, however, was initiated after the transferof seedlings to the experimental conditions. The increase inlength of the first three leaves, and to a lesser extent ofthe fourth leaf, was considerably smaller in comparison withthat of later formed leaves. Moreover, the morphology of thefirst three to four leaves was deviant, whereas the others showedthe normal compound leaf architecture. All these results indicatedthat the fifth leaf was the earliest formed leaf with growthcharacteristics that might reflect the growth potential of thewhole plant. Development of the fifth leaf was tested as a marker for wholeplant growth. At three temperature, 18, 15 and 12°C, growthresponses of the fifth leaf were similar to that of whole plantsin four tomato genotypes: Line A, Line B, Premier and MXXIV-13.Significant differences in relative growth rate of dry weightof whole plants and fifth leaves (RGR_W)and of leaf area of thefifth leaves (RGR_LA between two fast growing and two slow growinggenotypes were found. No genotype by temperature interactionfor RGR_W and RGR_LA was found, indicating that the effect oftemperature decrease was similar for the four genotypes. The structure of the mature fifth leaf of one fast and one slowgrowing genotype, Line A and MXXIV-13, was analysed. For bothgenotypes, leaves were small and thick at low temperature, 12°C.The total number of epidermis and palisade parenchyma cellsper leaf was smaller but the size of the cells developed at12°C was larger than at 18°C. Consequently, the slowgrowth at 12°C was due to a low rate of cell division. Atboth temperatures, the fifth leaf to MXXIV-13 was smaller comparedto that of line A. Since the size of the cells were similar,the smaller leaf size was due to lower number of leaf cells. The results confirm the suitability of the growth, especiallyexpressed as RGR_LA , of the fifth leaf as a nondestructive marketfor vegetative development of tomato at low temperature. Growthdifferences between genotypes were mainly reflected by differencesin cell number of leaves, which might be correlated with geneticallydetermined differences in cell number of leaf primordia.Copyright1993, 1999 Academic Press Lycopersicon esculentum Mill. genotypes, plant growth, selection criteria, low temperature, leaf initiation, leaf development, RGR, leaf structure, cell expansion     

Amylolytic Activity and Carbohydrate Levels During the Stamen Ontogeny of a Male Fertile, and a 'Gibberellin-Sensitive' Male Sterile Mutant of Tomato (Lycopersicon esculentum)

The activity of amylases, and the level of starch and solublesugar content were analysed in the normal (+/+), a ‘gibberellin-sensitive’male sterile stamenless-2 (sl-2/sl-2) mutant, and GA³-revertedsl-2/sl-2 mutant stamens of tomato (Lycopersicon esculentumMill.), at various stages of development. In the mutant stamens,amylolytic activity did not differ from that of the normal untilthe tetrad stage, but thereafter it was significantly lowerthan that of normal stamens. The starch content also did notdiffer in the two lines at early stages of development. However,at later stages it decreased in normal stamens, whereas it remainedunchanged in the mutant. The soluble sugar content graduallyincreased during the development of normal stamens. But in mutantstamens, it remained the same throughout development and wassignificantly lower than the normal. In GA₃-reverted mutantstamens, the amylolytic activity and the level of starch andsoluble sugars were comparable to normal stamens. It is proposedthat the sl-2/sl-2 mutation, through its effects on endogenousgibberellins, affects the activity of amylases which, in turn,result in lower sugar levels leading ultimately to abnormalpollen development. Key words: Amylases, male-sterility, tomato     

Short- and Long-Term Inhibition of Respiratory Carbon Dioxide Efflux by Elevated Carbon Dioxide

Dark carbon dioxide efflux rates of recently fully expandedleaves and whole plants of Amaranthus hypochondriacus L., Glycinemax (L.) Merr., and Lycopersicon esculentum Mill. grown in controlledenvironments at 35 and 70 Pa carbon dioxide pressure were measuredat 35 and 70 Pa carbon dioxide pressure. Harvest data and whole-plant24-h carbon dioxide exchange were used to determine relativegrowth rates, net assimilation rates, leaf area ratios, andthe ratio of respiration to photosynthesis under the growthconditions. Biomass at a given time after planting was greaterat the higher carbon dioxide pressure in G. max and L. esculentum,but not the C₄ species, A. hypochondriacus. Relative growthrates for the same range of masses were not different betweencarbon dioxide treatments in the two C₃ species, because highernet assimilation rates at the higher carbon dioxide pressurewere offset by lower leaf area ratios. Whole plant carbon dioxideefflux rates per unit of mass were lower in plants grown andmeasured at the higher carbon dioxide pressure in both G. maxand L. esculentum, and were also smaller in relation to daytimenet carbon dioxide influx. Short-term responses of respirationrate to carbon dioxide pressure were found in all species, withcarbon dioxide efflux rates of leaves and whole plants lowerwhen measured at higher carbon dioxide pressure in almost allcases. Amaranthus hypochondriacus L., Glycine max L. Merr., Lycopersicon esculentum Mill., soybean, tomato, carbon dioxide, respiration, growth     

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     

The Meristem and Quiescent Centre in Cultured Root Apices of the gib-l Mutant of Tomato (Lycopersicon esculentum Mill.)

Cultured root apices of tomato bearing the gib-I mutation, whichreduces the levels of endogenous gibberellins, grew slower andwere thicker than wild-type contols. This was the result ofshorter and broader cells in the menstem of the mutant. Cellsof both cortex and stele were affected, but this did not causeany alteration to the volume fraction occupied by these twotissues in the root meristem. Root caps were longer in the mutantand there were also more layers of rhizodermis. All these effectscould be reproduced in wild-type roots by addition of 0.1µM2S, 3S paclobutrazol (an inhibitor of gibberellin biosynthesis)to the culture medium and could be normalized in mutant rootsby 0.1 µM GA₃. Cell doubling times in the proximal regionof the meristem were similar in mutant and wild-type roots,but were faster in both the quiescent centre (QC) and the capmeristem of the mutant. This latter feature of the mutant rootsis likely to be the cause of their longer caps, while the fasterrate of division in the QC accounts for the additional tiersof cells that were found to build up in the cortical portionof this zone These additional tiers failed to form in mutantroots grown in GA₃, but they could be induced in wild-type rootsby 2S, 3S paclobutrazol. These results suggest that endogenousgibberellins may be partly responsible for the slow rate ofcell growth and proliferation in the QC. Gibberellins, gib-I mutation, Lycopersicon esculentum, meristem, roots, 2S, 3S paclobutrazol, quiescent centre, tomato     

The Relation Between the Nitrogen Concentration and Photosynthetic Capacity of Potato (Solanum tuberosum L.) Leaves

Measurements of the rate of light-saturated photosynthesis (P_max)were made on terminal leaflets of potato plants growing in cropssupplied with 0, 3, 6, 12, 24 and 36 g N m^–2. Measurementswere made between 100 and 154 d after planting. Two types ofleaf were selected—the fourth leaf on the second-levelbranch (L₄, _B1) and the youngest terminal leaflet that was measurable(L_YM). Later, the total nitrogen concentration of each leaflet(N_L) was measured. A linear regression between P_max and N_L,common to both leaf positions, explained 68.5% of the totalvariation. With L₄, _B1 leaves there was a significant improvementin the proportion of variation explained when regressions withseparate intercepts and a common slope were fitted to individualfertilizer treatments. These results suggest that an increasingproportion of leaf nitrogen was not associated with the performanceof the photosynthetic system with increasing nitrogen supply.This separation between nitrogen treatments was not as clearfor L_YM leaves. Stomatal conductance to transfer of water vapourwas neither influenced by leaf position nor directly by nitrogensupply. Rather conductance declined in parallel with the declinein photosynthetic capacity. Solanum tuberosum, potato, nitrogen, photosynthesis, stomatal conductance, leaf     

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     

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.     

The Import and Redistribution of Several Cations and Anions in Tomato Leaves

Wolterbeek, H. Th. and De Bruin, M. 1986. The import and redistributionof several cations and anions in tomato leaves.—J. exp.Bot. 37: 331–340. The upward movements in the xylem and redistribution from theleaf of Na⁺ , K⁺ , Rb⁺, Cs⁺ and four anions were examined insub-systems of tomato plants (Lycopersicon esculentum, Mill.cv. Tiny Tim). There was a delay with respect to the redistributionof newly imported elements from the source leaf of about 16–20h for all four alkali ions. This is considerably less than theapparent delay for the anions Sb(SO₄)^– WO₄^2– Mo₇O₂₄^6–and AsO₄^3– The prolonged delay for the anions is suggestedto be a consequence of metabolic transformation in the leaf.Reduction of the source-sink activity ratio did not decreasethe delay period from the source leaf, but apparently causedincreased Na⁺ transfer from the xylem. It is concluded thatthe application of a detailed mathematical descnption of upwardelement movement has considerable potential possibilities forunderstanding circulation of nutrients in the plant. Key words: Alkali ions, anions, xylem, phloem, redistribution, tomato     

Effect of Disbudding on Root Cytokinin Export and Leaf Senescence in Tomato and Tobacco

Bud removal and decapitation (disbudding) of plants of tomato(Lycopersicon esculentum Miller) and tobacco (Nicotiana tabacumL.) resulted in an increase in both the concentration and thetotal flux of cytokinin in bleeding xylem sap. There was a retardationin the rate of chlorophyll loss from leaves of disbudded plantsof both species. Ultrastructural examination of the chloroplastsof disbudded tomato plants revealed a maintenance of chloroplastintegrity, compared with chloroplasts from control plants. Itis suggested that the delaying of leaf senescence observed indisbudded plants is due to an increased availability of cytokininto these leaves.     

Analysis of Low-temperature Tolerance of a Tomato (Lycopersicon esculentum) Cybrid with Chloroplasts from a more Chilling-tolerant L. hirsutum Accession

Growth and photosynthesis of an alloplasmic tomato (cybrid),i.e. line AH47, containing the nuclear genome of the chilling-sensitivecytoplasmic albino mutant of L. esculentum Mill. ‘LargeRed Cherry’ (LRC) and the plastome of a more chilling-toleranthigh-altitude accession of the related wild species L. hirsutumHumb. & Bonpl. LA 1777, were investigated at an optimal(25/20°C) and suboptimal (16/14°C) day/night temperatureregime and their performance compared with that of both euplasmicparents. The cybrid shoot had a similar biomass and developmentrate to the nuclear tomato (L. esculentum) parent at both temperatureregimes. Compared with the biomass production of shoots grownat optimal temperature, the reduction in shoot biomass at suboptimaltemperature was smaller for L. hirsutum than for L. esculentumand the cybrid. This difference was related to a stronger inhibitionof leaf area expansion in L. esculentum and the cybrid in thesuboptimal temperature regime than in L. hirsutum. Irrespectiveof the temperature regime under which the plants were grown,photosynthetic performance and leaf pigment, carbohydrate andsoluble-protein contents of the cybrid resembled those of thenuclear parent. No advantages of the alien L. hirsutum chloroplastwith respect to growth and photosynthesis-related characteristicswere observed in the cybrid in the suboptimal temperature regime,indicating that the temperature sensitivity of the photosyntheticapparatus is regulated by nuclear genes. An adverse consequenceof interspecific chloroplast transfer was the increased susceptibilityto chill-induced photoinhibition of the cybrid. It is concludedthat cybridization is not a useful tool for improving low-temperaturetolerance of tomato. Copyright 2000 Annals of Botany Company Alloplasmic tomato, chloroplast, cybrid(ization), growth, low-temperature tolerance, Lycopersicon esculentum, L. hirsutum, photosynthesis, plastome, tomato     

The Role of Roots in Control of Bean Shoot Growth

Restriction of root growth by growing bean plants (Phaseolusvulgaris L.) in very small pots led to the development of dwarfplants. The leaves of those plants were smaller and their internodesshorter than those of control plants which were grown in largerpots and had developed a more extensive root system. A largequantity of starch—much more than in control plants —accumulated in the leaves and shoots of the dwarf plants. Increasingthe amount of minerals which was supplied to the roots, enhancedleaf growth of the control plants but failed to affect the dwarfones, in spite of the fact that in both cases the treatmentincreased the content of N, P and K in all the plant organs.The leaf water content was similar in both treatments, but theleaf water potential was higher in the dwarf plants. Exogenousapplication of gibberellic acid (GA₃) to the dwarf plants overcamethe reduction of stem growth completely, and that of the leavespartially. Application of the cytokinin, benzyladenine (BA)did not affect stem growth, but increased that of the primaryleaves. A combined supply of GA₂ + BA restored completely thegrowth of the stem and the primary leaves, and partially thatof the trifoliate leaves. It is concluded that a limited rootsystem restricts shoot growth through an hormonal system inwhich at least gibberellins and cytokinins are involved, andthat the dwarfing is not a consequence of mineral or assimilatedeficiency, or due to water stress. Phaseolus vulgaris L., leaf growth, stem growth, root restriction, gibberellic acid, benzyladenine, cytokinin     

Systemic Responses Arising From Localized Heat Stimuli in Tomato Plants

Localized application of heat to the terminal leaflet of leaf1 of tomato (Lycopersicon esculentum) seedlings induced bothpropagated electrical activity and the systemic production ofproteinase inhibitors. Aspirin and related compound inhibitedboth the propagated electrical activity and the systemic response.An electrical signal therefore remains a candidate for the systemicsignal in the wound response of tomato plants Proteinase inhibitor, propagated electrical activity, aspirin, tomato, Lycopersicon esculentum     

An Analysis of the Effects of Gibberellic Acid on Tomato Leaf Growth

The effects of four consecutive daily sprays of gibberellicacid (GA₃) on the growth of leaves of young tomato plants cv.Potentate were studied. Total leaf weight and area were increasedby GA₃. The percentage changes were larger in the younger leavesthan in the older but the absolute increases of the middlleleaves accounted for most of the total response. Chlorophyllcontent, both total and per unit weight, was reduced by GA inthe older leaves and increased in the younger; on an area basisit was reduced in all but the youngest leaves. Palisade cell length and palisade cell number per unit sectionlength were reduced by GA₃ in the oldest leaves and increasedin the youngest. There were larger intercellular spaces in bothmesophyll layers and a larger transectional area of the mid-ribsof the oldest and two youngest leaves in GA₃ plants. The ‘surfaceareas’ of epidermal cells were also increased by GA₃ treatment.Leaf fresh weight per unit area was only a true index of laminathickness in the two oldest leaves.     

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     

An Evaluation of the Effects of Ethylene on Carbon Assimilation in Lycopersicon esculentum Mill

Leaf and whole plant gas exchange rates of Lycopersicon esculentumMill, were studied during several days of continuous exposureto ethylene. Steady-state photosynthesis and transpiration ratesof control and ethylene-treated individual leaves were equivalent.However, the photosynthesis and transpiration rates of treatedleaves required at least five times longer to reach 50% of thesteady-state rate. This induction lag was attributed to ethylene—inducedleaf epinasty and temporary acclimation to lower incident lightlevels immediately prior to measurement of gas exchange. Thewhole plant net carbon exchange rate (NCER) of a representativetreated plant was also reduced by 51% after 24 h exposure toethylene relative to both its pre-treatment rate and that ofthe control. Ethylene exposure reduced the growth rate of thetreated plant by 50% when expressed as carbon (C) gain. Theinhibition of NCER and growth rate associated with epinastywas completely reversed when the epinastic leaves were returnedto their original positions and light interception was re-established.The results demonstrate that the inhibition of whole plant CO₂assimilation is indirect and due to reduced light interceptionby epinastic leaves. Morphological changes caused by environmentalethylene are thus shown to reduce plant C accumulation withoutinhibiting leaf photosynthesis processes per se. Key words: Ethylene, carbon assimilation, growth