The Preservation of Plant Cells, particularly Sieve Tubes, by Vacuum Freeze-drying

A vacuum freeze-drying apparatus is described. Cell contentswere preserved in small, rapidly frozen pieces of plant tissuedried for four hours at – 30° C. After drying, specimenswere either directly embedded with the resin ‘Epikote’or fixed with 2 per cent osmium tetroxide in benzene and subsequentlyembedded in ester wax or Epikote resin. Mesophyll cells and border parenchyma cells were preserved inleaf pieces, and cell contents are comparable with the protoplastsof living cells. In soybean leaf, files of parenchyma cellsoccur between palisade and spongy mesophyll cells, linking fineveins. Hand sections of frozen-dried Epikote-embedded petiolephloem from Primula obconica revealed a mature sieve tube containingstrands. Preservation by freeze-drying is taken as conclusiveevidence for the existence of transcellular strands in livingsieve tubes.     

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     

Leaf-like Structure in the Photosynthetic, Succulent Stems of Cacti

This research examined the hypothesis that as cacti evolve tothe leafless condition, the stem epidermis and cortex becomemore leaflike and more compatible with a photosynthetic role.All cacti in the relict genus Pereskia have non-succulent stemsand broad, thin leaves. All members of the derived subfamilyCactoideae are ‘leafless’, having an expanded cortexthat is the plant's only photosynthetic tissue. In Pereskia,leaves have a high stomatal density (mean: 50.7 stomata mm^–2in the lower epidermis, 38.1 mm^–2 in the upper epidermis),but stems have low stomatal densities (mean: 11.3 mm ₂, threeof the species have none). Stems of Cactoideae have a high stomataldensity (mean: 31.1 mm^–2, all species have stomata). Theouter cortex cells of stems of Cactoideae occur in columns,forming a palisade cortex similar to a leaf palisade parenchyma.In this palisade cortex, the fraction of tissue volume availablefor gas diffusion has a mean volume of 12.9%, which is identicalto that of Pereskia leaf palisade parenchyma. Pereskia stemcortex is much less aerenchymatous (mean: 5.3% of cortex volume).Cactoideae palisade cortex has a high internal surface density(0.0207 cm₂ cm^–2 which is higher than in Pereskia stemcortex (0.0150 cm₂ cm^–3) but not as high as Pereskia leafpalisade parenchyma (0.0396 cm₂ cm^–3). Pereskia stem cortexhas no cortical bundles, but Cactoideae cortexes have extensivenetworks of collateral vascular bundles that resemble leaf veins. Cactaceae, cactus, intercellular space, stomatal density, internal surface/volume, evolution     

Processes modulating calcium distribution in citrus leaves. An investigation using x-ray microanalysis with strontium as a tracer

Citrus leaves accumulate large amounts of calcium that must be compartmented effectively to prevent stomatal closure by extracellular Ca2+ and interference with Ca(2+)-based cell signaling pathways. Using x-ray microanalysis, the distribution of calcium between vacuoles in different cell types of leaves of rough lemon (Citrus jambhiri Lush.) was investigated. Calcium was accumulated principally in palisade, spongy mesophyll, and crystal-containing idioblast cells. It was low in epidermal and bundle sheath cells. Potassium showed the reverse distribution. Rubidium and strontium were used as tracers to examine the pathways by which potassium and calcium reached these cells. Comparisons of strontium and calcium distribution indicated that strontium is a good tracer for calcium, but rubidium did not mirror the potassium distribution pattern. The amount of strontium accumulated was highest in palisade cells, lowest in bundle sheath and epidermal cells, and intermediate in the spongy mesophyll. Accumulation of strontium in palisade and spongy mesophyll was accompanied by loss of potassium from these cells and its accumulation in the bundle sheath. Strontium moved apoplastically from the xylem to all cell types, and manipulation of water loss from the adaxial leaf surface suggested that diffusion is responsible for strontium movement to this side of the leaf. The results highlight the importance of palisade and spongy mesophyll as repositories for calcium and suggest that calcium distribution between different cell types is the result of differential rates of uptake. This tracer technique can provide important information about the ion uptake and accumulation properties of cells in intact leaves.     

Effects of Leaf Age and Position on the Shoot Axis on Potassium Absorption by Tomato Leaf Slices

The effect of leaf age on K (⁸⁶Rb) influx into tomato (Lycopersiconesculentum Mill.) leaf lamina slices was determined for leaves5, 9 and 13 counting acropetally. Potassium influx rates expressedon a leaf fresh weight basis declined rapidly during leaf elongationat external KCI concentrations between 0.5 and 20.0 mM. In fullyexpanded leaves, K influx rates declined more slowly with age.The onset of senescence in mature leaves did not result in alarge loss in K uptake capability. Leaf position on the shootaxis and the stage of whole plant development had little influenceon K influx into leaf cells. It is suggested that the rapiddecrease in K influx in growing leaves is related to a dilutionin the concentration of K transporter sites resulting from anincrease in cell volume and weight. Lycopersicon esculentum Mill, tomato, free space, potassium, influx rate, ion uptake, leaf slices, leaf age leaf ontogeny     

Comparison between the anatomical and morphological structure of leaf blades and foliar domatia in the ant-plant Hirtella physophora (Chrysobalanaceae)

Background and Aims: Myrmecophytes, or ant-plants, are characterized by their abilityto shelter colonies of some ant species in hollow structures,or ant-domatia, that are often formed by hypertrophy of theinternal tissue at specific locations (i.e. trunk, branches,thorns and leaf pouches). In Hirtella physophora (Chrysobalanaceae),the focal species of this study, the ant-domatia consist ofleaf pouches formed when the leaf rolls over onto itself tocreate two spheres at the base of the blade. Methods: The morphological and anatomical changes through which foliarant-domatia developed from the laminas are studied for the firsttime by using fresh and fixed mature leaves from the same H.physophora individuals. Key results: Ant-domatia were characterized by larger extra-floral nectaries,longer stomatal apertures and lower stomatal density. The anatomicalstructure of the domatia differed in the parenchymatous tissuewhere palisade and spongy parenchyma were indistinct; chloroplastdensity was lower and lignified sclerenchymal fibres were morenumerous compared with the lamina. In addition, the domatiawere thicker than the lamina, largely because the parenchymatousand epidermal cells were enlarged. Conclusions: Herein, the morphological and anatomical changes that permitfoliar ant-domatia to be defined as a specialized leaf structureare highlighted. Similarities as well as structural modificationsin the foliar ant-domatia compared with the lamina are discussedfrom botanical, functional and mutualistic points of view. Theseresults are also important to understanding the reciprocal evolutionarychanges in traits and, thus, the coevolutionary processes occurringin insect–plant mutualisms.     

Allometric Relationships in Field-grown Soybean

Allometric relationships in plants uncover size-correlated variationsin form and development and characterize the relative growthof a part of a plant in comparison with a whole. Stable allometricrelationships in ontogeny can be used as components of cropmodels and to estimate plant parameters that are difficult tomeasure. Our objective was to discover whether stable allometricrelations exist in ontogeny of field-grown soybeans (GlycinemaxL.). We used field data on vegetative stages, plant height,stem weight, and leaf weight of 16 soybean cultivars measuredon farms and on the experiment station of Mississippi StateUniversity during 1993–1995 growing seasons. The numberof observed crops for each cultivar ranged from one to 14. Stemheights displayed linear log-log dependencies on the vegetativestage, before and after the breakpoint stage, which typicallywas between the ‘fourth node’ and ‘sixth node’vegetative stages. Slopes of the log-log dependencies afterthe breakpoint stage were similar in all cultivars. Stem masshad log-log linear dependencies on stem height. Slopes of thesedependencies differed among cultivars grown under the same conditions,and among crops of the same cultivar grown under different conditions.Water stress could be a modifier of these relationships. Theproportion of leaf weights in the total weight of leaves andstems decreased linearly as the vegetative development progressed.Since allometric relations are stable for a specific crop, theycan be used to forecast vegetative development as soon as theyare established.Copyright 1998 Annals of Botany Soybean,Glycine maxL., allometry, vegetative development.     

Localization of Thermo-Osmotically Active Partitions in Young Leaves of Nuphar lutea

The submerged roots and rhizomes of the aquatic vascular macrophyteNuphar lutea (L.) Sm. are aerated, at least in part, by pressurizedventilation. Depending on temperature differences of up to 5K between the inside of young, just-emerged leaves and the surroundingair, pressure differences of 79 to 100 Pa higher than atmosphericare detectable inside the lacunuous spongy parenchyma of theleaf blades. The pressurization is a consequence of structuralfeatures of leaf tissues separating the air filled spaces ofthe spongy parenchyma from the atmosphere. These tissues areacting as thermo-osmotic partitions. Whereas the dimensionsof the stomatal openings (about 5·6 x 2·4 µm)and of the intercellular spaces of the palisade parenchyma (diametersabout 15 µm) are too large, those of the monolayers ofcells separating the palisade and the spongy parenchyma (diameters:0·7–1·2 µm) are small enough to impedefree gaseous diffusion. This inner non-homogeneous partitioninggives rise to the so-called Knudsen diffusion, a physical phenomenonleading to pressurization of the warmer air inside the spongyparenchyma. The rising pressure difference is strong enoughto establish an air flow through the aerenchyma of the wholeplant and out of the most porous older leaves in which a temperatureinduced pressurization is never detectable. These thermo-osmoticallyactive leaves enhance the influx of air to the rhizome and thediffusion path for oxygen to the roots is shortened to the distancebetween rhizome and root tips. Therefore, pressurized ventilationin Nuphar is seen to be of considerable ecological importancefor plant life in anaerobic environments. Key words: Aeration, leaf anatomy, thermo-osmosis of gases, Nuphar lutea     

Vascular Organization and some Aspects of the Morphology of the Rhizome of Gymnogrammitis dareiformis

Gymnogrammitis dareiformis, the taxonomically controversialdavalliaceous fern has a parenchymatous rhizome, in the groundtissue of which groups of 1–16 thick-walled cells (withpeg-like protrusions on inner walls) are irregularly scattered.Paleae clothing the rhizome are basally attached, gland-tippedand bearing unicellular marginal hairs. The vascular cylinderis a radially-symmetric dictyostele dissected by spirally-arrangedleaf gaps into slender reticulated meristeles. Some of the dorso-laterallyplaced leaves alone are fully developed; most other leaves aresuppressed and some are highly reduced (the larger reduced leavesappear as protrusions on the rhizome and have a well-formedleaf base). The leaf trace of developed as well as the largerreduced leaves is a channel-shaped loose reticulum of four vascularstrands; the trace of the reduced leaves is smaller and endsblindly at the leaf base. The leaf trace of the smaller reducedleaves is vestigial and represented often by only a pair ofvascular strands fusing into one and ending blindly in the cortexof the rhizome. The leaf trace of suppressed leaves fuses backwith the stelar cylinder, forming a convex reticulum bridgingthe sides of the leaf gap. It is suggested that the characteristic stelar organizationof the Davalliaceae is derived by suppression of leaves froma radiallysymmetric dictyostele with spirally-arranged leafgaps as found in Nephrolepis and that Gymnogrammitis with itsreduced and suppressed leaves indicates the process of transition.The creeping solenostelic rhizome with two-ranked leaf arrangementcould be derived from an erectgrowing dictyostelic one by supppressionof leaves.     

Salt Tolerance in the Halophyte Suaeda maritima L. Dum.: Intracellular Compartmentation of Ions

The time-course of exchange of sodium and potassium ions fromroot and leaf material of the halophyte Suaeda maritima hasbeen followed and the data analysed according to the phenomenologyof efflux, or compartmental, analysis. Sodium ions were exchangedmuch more slowly (c. 4 times) from the vacuoles of leaf cellsof plants grown in sodium chloride than were potassium ionsfrom the vacuoles of leaf cells of plants grown either in similarconcentrations of potassium chloride or in low concentrationsof potassium. In plants grown in sodium chloride, sodium ionswere exchanged 9 times more slowly from the vacuoles of leafcells than from the vacuoles of root cells. The concentration of sodium ions in the cytoplasm of leaf cellsof plants growing in 340 mol m^–3 sodium chloride was estimatedto be 165 mol m^–3 when the average concentration in theleaf tissue was about 600 mol m^–3. As measured by movement from mature to developing leaves inintact plants; there was less in vivo retranslocation of ²²Naand ³⁶CI in plants growing in sodium chloride than there wasof ⁸⁶Rb in plants growing either in potassium chloride or innon-saline conditions. The results are discussed in terms of the concept and energeticsof compartmentation of ions in the cells of halophytes.     

A Comparison of Leaf Anatomy in Field-grown Gossypium hirsutum and G. barbadense

Gossypium hirsutum L. (upland cotton) and G. barbadense L. (Pimacotton) are two of the most important fibre producing cottonspecies in cultivation. When grown side-by-side in the field,G.hirsutum has higher photosynthetic and transpiration rates (Luet al., 1997. Australian Journal of Plant Physiology24: 693–700).The present study was undertaken to determine if the differencesin physiology can be explained by leaf and canopy morphologyand anatomy. Scanning electron microscopy was used to comparethe leaf anatomy of field-grown upland (‘Delta’and ‘Pine Land 50’) and Pima (‘S6’)cotton. Compared to G. hirsutum, mature leaves of G. barbadenseare larger and thinner, with a thinner palisade layer. G. barbadenseleaves show significant cupping or curling which allows fora more even absorption of insolation over the course of theday and much more light penetration into the canopy. AlthoughG. barbadense leaves have a 70–78% higher stomatal densityon both the abaxial and the adaxial surfaces, its stomates areonly one third the size of those of G. hirsutum. This resultsin G. barbadense having only about 60% of the stomatal surfacearea per leaf surface area compared to G. hirsutum. These resultsare indicative of the anatomical and physiological differencesthat may limit the yield potential of G. barbadense in certaingrowing environments. Copyright 2000 Annals of Botany Company Cotton, leaf anatomy, leaf development, photosynthesis, Gossypium hirsutum, Gossypium barbadense, stomatal density     

Effect of UV-B Radiation on Leaf Optical Properties Measured with Fibre Optics

Changes in the internal light microenvironment in leaves ofplants of Brassica campestris L. cv. Emma, B. carinata L., andMedicago saliva L. cv. Armour in response to exposure to UV-B(UV-B, 280–320 nm) radiation were measured using a fibreopticmicroprobe. Plants were exposed for 2 weeks either to high visiblelight or to supplemental ultraviolet-B radiation. The spectral regime (400–700 nm; PAR) was measured eithermidway through the leaf palisade or the spongy mesophyll. Afterexposure to UV-B radiation leaves of Brassica campesiris attenuatedtransmitted light more than the controls. At the same time bothforward and back scattered light increased in the palisade andspongy mesophylls. In contrast, UV-treatment of Medicago salivaleaves increased light transmission into the palisade, whilethe back scattered component showed little change. Leaves ofcariiwla showed little change in response to UV. Other responsesto UV-B radiation included increases in leaf thickness, decreasedtotal chlorophyll content, and changes in UV-B screening pigmentsand chlorophyll fluorescence induction kinetics. Brassica campestriswas most sensitive to exposure to enhanced levels of UV-B radiation,whereas leaves of B. carinata were the least sensitive. Ourdata indicate that exposure to UV-B radiation altered the lightmicroenvironment within leaves of the species different ways.These changes appeared to be caused by alterations in pigmentcontent and leaf anatomy. In turn, the altered distributionof PAR within the leaf could influence photosynthesis. Key words: Brassica campestris, Brassica carinata, fibre optics, light scattering, Medicago saliva, optical properties, ozone depletion, photosynthesis, ultraviolet radiation     

Observations on the Distribution of Mineral Elements in the Leaf of Wheat (Triticum aestivum L.), with Particular Reference to Silicon

Wheat (Triticum aestivum L. cv. Wheaton) plants were grown inwater culture or in soil. Basal leaves (B) were harvested after3 weeks from the water culture plants, while flag leaves werecollected from soil-grown material at the time of inflorescenceemergence (E0) and 7 d after emergence (E + 7). Mineral distributionin bulk frozen leaves was investigated using SEM and X-ray microanalysis.The elements detected were silicon, phosphorus, chlorine, sulphur,potassium and calcium. Potassium was present in all cell typesat all harvests, chlorine was almost entirely confined to theadaxial and abaxial epidermi, while sulphur was only rarelydetected in the E0 and E + 7 leaves. Phosphorus was presentat higher levels in the E + 7 leaves than in the B or E0 leaves.At the B harvest calcium was confined to the adaxial epidermalcells, but in the E0 and E + 7 leaves it was present in bothepidermi. Silicon was, initially, mainly detected in the abaxialepidermal cells, but in older (E + 7) leaves it was presentin both epidermi and in some internal tissues. Mineral transportwithin the leaf and ionic environment at silica deposition sitesare discussed. Wheat, Triticum aestivum L., leaf, mineral distribution, X-ray microanalysis, silicon, calcium     

Xylem Sap from Actinidia chinensis: seasonal Changes in Composition

Seasonal variation was followed in the content of total a-aminoacids, arginine, calcium, total carbohydrate, ß-galactosidaseactivity, magnesium, nitrate, phosphatase activity, phosphateand sulphate in vacuum-extracted xylem sap from Actinidia chinensisvar. hispida, the Chinese gooseberry or kiwifruit. There wasa marked increase in the concentration of most sap componentsjust prior to leaf emergence followed by a rapid decrease afterthe leaves had expanded. Experiments with excised extensionshoots showed that much of this spring-time increase in concentrationsof sap components was due to mobilization of nutrients withinthe shoot itself. Sap from the trunk and the older brancheschanged less in composition than did sap from the younger partsof the plant. The amplitude and direction of trends in concentrationof sap from the different parts of the plant varied with nutrientand with time. Analysis of vacuum-extracted xylem sap collectedduring periods of rapid transpiration from early summer onwardsgives a reliable indication of the composition of the transpirationstream. Actinidia chinensis, Chinese gooseberry, kiwifruit, storage reserves, xylem sap, amino acids, arginine, calcium, carbohydrate, ßgalactosidase, magnesium, nitrate, phosphatase, phosphate, potassium, sulphate     

RNA Synthesis in Phaseolus Chloroplasts: II. RIBONUCLEIC ACID SYNTHESIS IN CHLOROPLASTS FROM DEVELOPING AND SENESCING LEAVES

The rate of RNA synthesis in chloroplasts from the primary leavesof Phaseolus vulgaris L. cv. Canadian Wonder was measured invitro as plant age increased. The rate per leaf began to fallbefore the leaf was 70% expanded. At full expansion, activityhad fallen by 70%. Chloroplast RNA synthesis per unit chlorophyllwas falling before the leaf was 25% expanded. When all parts of the plant above the mature primary leaveswere removed (detopping) chloroplast RNA synthesis in theseleaves rose within 36 h. The rate increased to a maximum 3–4d after detopping, when it was 5–10 times control values;thereafter it fell again. The chlorophyll content began to increaseabout 4 d after detopping, eventually rising by 100%. Detoppingcaused a 3-fold increase in the Triton X-100-soluble DNA contentof chloroplast preparations, measured after 3.5 d. At that timethe rate of RNA synthesis per unit Triton-soluble DNA was thesame in chloroplasts from the primary leaves of intact and detoppedplants. Detopping also resulted in an increase in the depthof the leaf palisade layer. The effects of detopping on chloroplasts were prevented by darknessand reduced by shading. Increased chloroplast RNA polymerase activity was also inducedin the primary leaves by placing a polythene bag over intactplants, enclosing everything above these leaves. Removal ofthe roots from detopped plants prevented the rise in the rateof chloroplast RNA synthesis.     

Relative anion permeabilities and concentrations in leaf cells of Pisum sativum determined using electrical measurements and the Goldman equation

The electrical potential difference across the tonoplast ofpalisade mesophyll cells of leaves of Pisum sativum was 6.6± 0.8 mv (positive in the vacuole). The potential acrossthe plasmalemma depended on the particular anion accompanyingpotassium in the external solution. Assuming that the plasmalemmapotentials were diffusion potentials that could be analyzedusing the Goldman equation, the permeabilities of pyruvate,formate, .butyrate, acetate and bicarbonate into the cells werecalculated to be large compared with that of potassium, whilethe chloride permeability was relatively low. The upper limitsfor concentrations in the cytoplasm of palisade mesophyll cellsin pea leaves were as follows: potassium, 98 mM total monovalentorganic acids, 0.4 mM and bicarbonate, 0.2 mM. (Received March 3, 1971; )     

Stomata and Structure of Tetraploid Apple Leaves cultured in Vitro

Leaves of anther-derived tetraploid apple (Malus pumila Mill.)shoots were examined by low-temperature scanning electron microscopy(LT-SEM). Leaves were serrate and wide with an undulating adaxialsurface due to convex epidermal cells, apparently without crystallineepicuticular wax. Stomata were absent from the adaxial surface,except for the marginal teeth which exhibited 40-60 stomataper leaf; they probably originated from residual mitotic activity.One third of abaxial stomata was occluded by the residual cuticleof the mother guard cell across the stomatal pore which rupturedwhen the stomata became functional. The stomatal index was 7·2(± 1·6) with 60-75 stomata mm^-2, i.e. abaxialstomata of tetraploid leaves expanded in vitro were less frequentthan those in triploid leaves either cultured in vitro (475-575stomata mm^-2) or grown on the tree (320-390 stomata mm^-2) wherethe stomatal index was 21 (± 4). Freeze-fracture transsectionsshowed that the tetraploid in vitro leaves were composed ofa layer of adaxial epidermal cells, followed by a single layerof palisade cells and four to five layers of spongy mesophyllcells and the abaxial layer of epidermal cells, in contrastto juvenile seedling-grown apple leaves in which the two layersof palisade cells comprised the majority (52-60%) of the leafvolume. The same morphological features, such as wide and lesspointed leaves, reduced stomatal density and stomatal index,and increased stomatal size that were previously reported fortree-grown tetraploid leaves were also expressed in vitro. Thus,causes of the stomatal deformation in tissue-cultured Rosaceaeare interpreted to be in part genetic and not purely environmental.Copyright1994, 1999 Academic Press Malus pumila Mill., apple, biotechnology, breeding, cryo-preservation, CO₂, juvenile, low temperature-scanning electron microscopy (LT-SEM), micropropagation, ploidy, stomata, tissue-culture, transpiration     

Cellular Structure and Light Absorbtion in Leaves of Frithia pulchra (Mesembryanthemaceae)

In order to quantify the structural differences between celltypes of leaves from a ‘ window’ plant, an ultrastructuralmorphometric analysis was made of the epidermal, window andchlorenchyma tissues of Frithia pulchra. Epidermal cells arethe largest cells found in Frithia leaves and are characterizedby the presence of a thick outer tangential cell wall and numerousvacuolar inclusions. Epidermal tissue has an optical densityof 0.30. The transparent window tissue (i.e. optical density= 0.08) has a uniform ultrastructure throughout the length ofthe leaf. The vacuome comprises aproximately 97 per cent ofthe protoplasmic volume of window cells. Chlorenchyma cellspossess thin cell walls and are surrounded by numerous intercellularspaces. Cells of the apical chlorenchyma tissue possess approximately30 plastids per cell. These chloroplasts have an average individualvolume of 220 µm². Cells of the basal chlorenchyma tissuecontain chloroplasts that are five to six times smaller andmore numerous than those in cells of the apical chlorenchyma.The increased volume of chloroplasts in the apical comparedwith basal chlorenchyma cells (i.e. 31.4 and 20.2 per cent ofthe protoplasm, respectively) is positively correlated withtheir optical densities of 1.46 and 0.97, respectively. Frithia pulchra, stereology, leaf, light absorption, window plant     

Net Accumulation of Minerals and Water and the Carbon Budget in an Expanding Leaf of Tomato

The changes in f. wt, d. wt, nitrogen, potassium, calcium, phosphorus,magnesium and carbon of the seventh leaf of a tomato plant weremeasured at seven occasions from 10 days to 30 days after leafemergence. Measurements of CO₂ exchange by the leaf during bothlight (70 W m^–2, 7 h) and dark (17 h) periods and thechange in carbon content over these two periods enabled a carbonbalance to be constructed on these seven occasions. Changesin the sugars and starch contents of the leaf over these twoperiods at each occasion were measured. With the exception of calcium the rates of accumulation of allsubstances increased to their maxima when the leaf was 22–24-days-old.Carbon fixation per unit f. wt. increased to a maximum whenthe leaf was 16-days-old. In a 10-day-old leaf the rate of carbonfixation was already four-fifths of maximum and one-quartermore than that at 30 days. The rate of night respiratory lossof carbon per unit fresh weight decreased as the leaf expanded.In a 10-day-old leaf, the amount of carbon lost by night respirationaccounted for one-quarter of that fixed in the same day. Thisfraction fell to one-tenth when the leaf was 22-days-old andremained constant thereafter. The amount of carbon being importedto the leaflets of a 10-day-old leaf was less than one-quarterof that accumulated in 1 day. Thus, the contribution of theimported carbon to the leaf growth up to this stage is relativelysmall. The transition of the seventh leaf from being a net importerto being a net exporter occurred when the leaf was 13-days-old. The sucrose content per unit f. wt was higher in the youngerthan in the older leaves and was not correlated to the transitionfrom net import to net export. The accumulation and breakdownof starch in a leaf were related not only to the growth of theleaf but also to the development of the whole plant. Lycopersicon esculentum, tomato, leaf, accumulation of minerals, water content, carbon budget