The Developmental Anatomy of the Root System in Yam Bean, Pachyrhizus erosus Urban

Investigations revealed that the anatomy of the primary radicularroot of yam bean (Pachyrhizus erosus L.) was typically dicotyledonousexcept that the xylem was not completely developed centripetally.Most of the roots had tetrarch xylem, although a few triarchand pentarch roots were also observed. In both tuberous andnon-tuberous roots, secondary thickening occurred by the formationof the meristematic vascular cambium which formed secondarytissues in a normal fashion. Subsequently, tuberization wasinitiated in the secondary xylem by the development of anomalous‘secondary’ cambia from parenchyma cells surroundingvessel elements. Anomalous ‘secondary’ cambia alsodeveloped from parenchyma cells not associated with vessels.Subsequently, anomalous ‘tertiary’ cambia differentiatedfrom tissues produced by the anomalous ‘secondary’cambia. Activities of these anomalous cambia resulted in theproduction of parenchyma storage cells and were chiefly responsiblefor the growth of the mature tuber. Pachyrhizus erosus L., yam bean, tuberous root, anatomy, anomalous ‘secondary’ cambia, anomalous ‘tertiary’ cambia, centripetal xylem development     

Leaf Anatomy, Emphasizing Unusual 'Concertina' Mesophyll Cells, of Two East African Legumes (Caesalpinieae, Caesalpinioideae, Leguminosae)

Cordeauxia edulis (Somalia and Ethiopia), andStuhlmannia moavii(Tanzania, Kenya and Madagascar) are evergreen shrubs or smalltrees of dry areas. They have similar leaf anatomy as revealedby resin sectioning and scanning electron microscopy. The cuticleis extremely thick and all vascular bundles lack bundle sheathextensions. The most unusual feature is the mesophyll, threeto seven layers consisting entirely of cylindrical palisadecells with lateral walls capable of changing vertical lengthby folding in a concertina-like manner. The matching outwardfolds of two adjacent cells always remain attached by meansof a row of wall thickenings (‘pegs’). The pegscan elongate, especially so between the widely separated mesophyllcells that occupy the substomatal chamber area. The unattachedflexible inward wall folds enable these ‘concertina’cells to shorten or lengthen vertically without disrupting cellinterconnections in the interior of each relatively long-livedleaf as it periodically loses and gains water. Concertina cellsmay be an anatomical adaptation allowing these leaves to remainevergreen and survive extended periods of drought and yet tostore water quickly when it becomes available. Leguminosae; Caesalpinioideae; Cordeauxia ; Stuhlmannia ; ‘concertina’ mesophyll cells; desert adaptation; hollow glandular trichomes; leaf anatomy; wall thickenings     

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     

Mucilage in Cacti: Its Apoplastic Capacitance, Associated Solutes, and Influence on Tissue 5

Mucilage content in the stems of four sympatric cactus speciesvaried from none for Ferocactus acanthodes, 19% by dry weightfor Opuntia basilaris, 26% for Opuntia acanthocarpa, and 35%for Echinocereus engelmannii. Although the mucilage differedchemically among the species (the arabinose content ranged from17% to 51% of the sugar monomers), its relative capacitance(change in relative water content per unit change in water potential)remained about 15 Mpa^–1. The relative capacitance of thewater-storage parenchyma averaged 1·04 Mpa^–1 andwas consistent with the mucilage content, being lowest for F.acanthodes and highest for E. engelmannii. Mucilage isolatedfrom hydrated tissue was accompanied by solutes with an osmoticpressure of about 0·2 MPa. Such associated solutes influencethe water-release characteristics of mucilage and hence itsrole as an apoplastic capacitor. In particular, extracellularsolutes can facilitate the release of appreciable mucilage-boundwater to the cells at tissue water potentials occurring duringthe initial phases of drought. Key words: Echinocereus engelmannii, Ferocactus acanthodes, Opuntia acanthocarpa, Opuntia basilaris, water potential isotherms     

Establishment, Structure and Morphology of the Tuber of Balanophora

During germination of the ‘seed’ of Balanophora,endosperm cells at the radicular pole grow out as tubular structuresand anchor the ‘seed’ to the host rootlet. The radiculartier of cells of the embryo elongate as primary haustorial tubesand establish contact with the host root vasculature. A secondaryhaustorium arises from a meristem adjoining the primary haustorium.The remainder of the embryo contributes to the tuber proper. Host parenchyma in the immediate vicinity of the primary haustoriumreverts to meristematic activity. Some of the derivatives matureas perforate tracheary cells. The remainder, retaining meristematicactivity, squeeze themselves between secondary haustorial cellsand together initiate a composite conducting strand, which repeatedlydichotomizes as the tuber grows. The conducting strand of Balanophora is looked upon as the equivalentof combined adventitious root system of parasite and host. Theremaining part of the tuber is equivalent to the shoot. Balanophora, tuber, morphology, host-parasite relations, parasite     

Identification of the Excitable Cells in the Petiole of Mimosa pudica by Intracellular Injection of Procion Yellow

Excitable cells in the petiole of Mimosa pudica were locatedby microelectrode technique and stained with Procion YellowMx4R which was previously filled in the electrode and injectediontophoretically into the cells. Microscopic observations ofsections of the stained petioles revealed that protoxylem parenchymacells and narrow phloem cells were excitable. The protoxylemlocalized just inside the metaxylem was composed almost entirelyof the parenchyma cells which were 106.3±5.2 µmlong (mean±EM, n=15) and 14.2±0.6 µm indiameter (n =33). The excitable phloem cells were 76.4±4.1µm long (n=7) and 7.0±0.3 pan in diameter (n=37)and were thought to be companion cells or narrow parenchymacells or both. Amplitudes of action potentials recorded fromthe petiolar surface had a linear relation to those from theexcitable cells in the same petiole. From this fact and thearrangement of excitable cells in the petiole, we conclude thatwhen the transmission of action potential takes place in thepetiole all excitable cells in it are activated. ¹ Present address: 1st Department of Physiology, Hamamatsu UniversitySchool of Medicine, Handa-cho 3600, Hamamatsu 431-31, Japan. (Received September 7, 1982; Accepted November 8, 1982)     

Distribution, Development and Structure of Resin Ducts in Guayule (Parthenium argentatum Gray)

The distribution, development and structure of resin ducts inguayule (Parthenium argentatum Gray), the second best sourceof natural rubber, have been studied. Resin ducts are widelydistributed in stem, root, leaf, petiole and peduncle. The ductsin the primary tissues are initiated schizogenously and theirfurther development is schizolysigenous. The ducts in the cortexof the root do not have a well-defined epithelium. Ducts developedfrom the vascular cambium are initiated and develop schizogenously.Both resin and rubber are produced in the epithelial cells ofresin ducts. While resin is secreted into the duct lumen, rubberis stored within these cells. Epithelial cells store more thanneighbouring parenchyma cells. Guayule, rubber, resin, ducts, epithelial cells     

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     

Sucrose Leakage from Isolated Parenchyma of Sugar Beet Roots

The kinetics of sugar efflux from slices of sugar beet rootswas investigated using washing solutions of different osmoticpressure and calcium concentration. The leakage of sucrose isstrongly reduced in solutions of high osmotic pressure (>0·8MPa) or high calcium concentration (10 mM). Turgor-dependentnecrosis of parenchyma cells (plasmoptysis) is the main causeof sucrose efflux from the tissue in hypotonic media with lowcalcium activity. This was shown by good correlation betweenthe percentage of leaked sucrose and the percentage of tissuewater, which was in the free space after the washing procedure.The kinetics of sugar leakage from beet root parenchyma is nobasis for the estimation of the sugar contents of the free spaceor the cytoplasm in situ.     

Dilated Endoplasmic Reticulum Cisternae in Differentiating Xylem of Minor Veins of Mimosa pudica L. Leaf

The differentiating tracheary elements in the xylem of minorveins in Mimosa pudica L. contain, as is usual, complete nucleateprotoplasts. Within the latter, dictyosomes with associatedvesicles and endoplasmic reticulum (ER) are prominent components.The ER cisternae show an uncommon feature of developing voluminousdilations accumulating finely fibrous material. Similar dilatedER cisternae occur in parenchyma cells associated with the trachearyelements. Most of the dilated cisternae are elongated, taperingat both ends, and almost circular in transections. They varyin size. The largest measured was 10 µm long and 3 µmwide. In the tracheary elements the cisternae break down asthe protoplast disintegrates. For a time, mature cells containfibrous material, apparently the product of the dilated cisternae,at least in part. In the parenchyma cells the dilated cisternaeare released into the vacuoles after the associated trachearyelements reach maturity. They become structurally modified anddisintegrate. The timing in the appearance and disintegrationof the dilated ER cisternae suggests that these structures havesome function with reference to the differentiation of trachearyelements in the xylem.     

Histology of Callogenesis and Somatic Embryogenesis Induced in Stem Fragments of Cork Oak (Quercus suber) Cultured In Vitro

Calluses able to produce somatic embryos were formed duringin vitro culture of shoot fragments of cork oak (Quercus suberL.).Histological monitoring of these fragments during cultureshowed that it was the cortical parenchyma cells which underwentdedifferentiation before calluses were formed by repeated divisions.The calluses consisted of parenchyma cells surrounded by a fewlayers of meristematic cells. Proembryos formed in groups aroundthe edge of some calluses. Histological examination showed thatthey were produced by the evolution of two different categoriesof cell: one category had the appearance of ‘embryogenic’cells with very thick walls, a small vacuole rich in starchand a well-developed nucleus with a prominent nucleolus. Theother cells were very bulky with large vacuoles; their morphologywas similar to that of suspensor cells encountered in embryogenesisin gymnosperms. The ontogenic stages were similar to those describedin zygotic embryos of the genus Quercus. Nevertheless, mostof the embryonic structures deviated from normal developmentand at all stages produced secondary proembryos. Cork-oak, Quercus suber L, histology, callogenesis, somatic embryogenesis, embryogenic cells, starch, secondary embryogenesis     

The Wood Parenchyma of Triplochiton scleroxylon K. Schum

Unusual features in the histology of the secondary xylem wererevealed during an investigation into growth-ring developmentin Triplochiton in Nigeria. The main observation was the presenceof two kinds of apotracheal parenchyma: (1) strands made uplongitudinally of 2 to 4 (occasionally more) cells containingstarch and, (2) empty fusiform strands, without cross-walls.Each kind of parenchyma formed ‘units’, i.e. uniseriatetangential rows of like strands between the wood-rays. The starchystrands (storage parenchyma) became more numerous towards theend of each growth ring.     

Pulmonary blood flow distribution has a hilar-to-peripheral gradient in awake, prone sheep

Walther, Sten M., Karen B. Domino, Robb W. Glenny, Nayak L. Polissar, and Michael P. Hlastala. Pulmonary blood flow distribution has a hilar-to-peripheral gradient in awake, prone sheep.J. Appl. Physiol. 82(2): 678-685, 1997.We examined the pulmonary blood flow distribution withintravenous fluorescent microspheres (15 µm) in nine prone,unanesthetized, lambs. Lungs flushed free of blood were air-dried attotal lung capacity and sectioned into~2-cm³ pieces. The pieces wereweighed, identified by lobe, and assigned spatial coordinates.Fluorescence was read on a spectrophotometer, and signals werecorrected for piece weight and normalized to mean flow. Pulmonary bloodflow heterogeneity was assessed by using the coefficient of variationof the flow data. The number of pieces (±SD) analyzed were 1,249 ± 150/animal. Heterogeneity of blood flow was 29.5 ± 6.5%(coefficient of variation = SD/mean). Pulmonary blood flow decreasedwith distance from hilus (P < 0.002) but did not change significantly with vertical height. Distance fromthe hilus was the best predictor of pulmonary blood flow (R² = 0.201) and,together with spatial coordinates and lobe, accounted for 33.7 ± 12.0% of blood flow variability. We conclude that pulmonary blood flowin the awake, prone sheep is distributed with a hilar-to-peripheral gradient but no significant vertical gradient.

     

Inhibition of Light-Stimulated Leaf Expansion by Abscisic Acid

Abscisic acid (ABA) applied to intact bean (Phaseolus vulgaris)leaves or to isolated leaf discs inhibits light-stimulated cellenlargement This effect may be obtained with 10^–4 molm^–3 ABA, but is more significant at higher concentrations.The inhibition of disc expansion by ABA is greater for discsprovided with an external supply of sucrose than for discs providedwith KC1, and may be completely overcome by increasing the KC1concentration externally to 50 mol m^–3. Decreased growthrate of ABA-treated tissue is not correlated with loss of solutesfrom growing cells, but is correlated with a decrease in cellwall extensibility. ABA does not prevent light-stimulated acidificationof the leaf surface, and stimulates the acidification of theexternal solution by leaf pieces. However, the capacity of thecell walls to undergo acid-induced wall loosening is diminishedby ABA-treatment. The possibility that ABA acts directly byinhibiting growth processes at the cellular level, or indirectlyby causing stomatal closure, is discussed. Key words: Phaseolus vulgaris, ABA, Inhibition, Leaf expansion     

Structural Characteristics and Fatty Acid Composition of Psophocarpus tetragonolobus Seeds

Winged bean (Psophocarpus tetragonolbtis) seed coat in the hilarregion consists of a double layer of sclereids, tracheid barand spongy parenchyma cells. This is contrasted to the seedcoat structure on either side of the hilar region, which hasa single layer of sclereids, columnar cells and crushed parenchymacells. Cotyledonary cells are large (50 to 100µm in diameter)and have cell walls 2·4 to 4·7 µm thickwith pit-pair structures. Protein bodies and lipid bodies arethe main structural components of the cytoplasm while only asmall number of starch granules are present in each cell. Themajor portion of the lipid can be removed by non-polar solventsand contains oleic and linoleic acids as the predominant unsaturatedfatty acids. High levels of behenic acid were present in both‘free’ and ‘bound’ lipids. Psophocarpus tetragonolobus (L.) DC., winged bean, seed structure, seed coat, protein bodies, lipid bodies, fatty acids, oleic acid, linoleic acid     

Junction Complexes between Sieve Tubes in the Secondary Phloem of Myrtaceae

Junction complexes of unusual structure form between neighbouringsieve tubes in the secondary phloem of Eucalyptus species. Thick-walledribs support thin-walled ‘sieve areas’. In longitudinalsections the structures have a ‘concertina’- likeappearance. They are relatively large, up to 0.2 mm in length.Electron micrographs confirmed that the structures consistedof thin-walled areas perforated with pores, supported by muchthicker ribs. The structures provide a vast surface area fortransfer of metabolites between sieve tubes compared with thatof lateral wall sieve areas of other plants. Hydrolysis of parenchymacell walls occurs during the development of the junction complexes.The structures are only found when sieve tubes are in closeproximity and it is the redifferentiation and partitioning ofintervening parenchyma cells which result in junction complexformation. A survey for the presence of the structures in thephloem of other genera in the family Myrtaceae was made andthey were found in Tristania and Angophora but were not observedin Acmena and Metrosideros. Eucalyptus, sieve tubes, lateral walls, ultrastructure     

The Nuclear Endoreduplication Cycle in Metaxylem Cells of Primary Roots of Zea mays L.

The nuclear DNA content of metaxylem cells in roots of Zea mayscv. Golden Bantam reaches 16C or 32C by successive rounds ofDNA endoreduplication. Each phase of endoreduplication (endo-S)is separated by a non-DNA synthetic phase (endo-G). These phasesseem to occur in zones at fixed distances from the root tip.The duration of the phases in two of the endoreduplication cycles(4C–8C, 8C–16C) has been estimated in two ways.The first makes use of the rate of movement of cells throughthe positions along the root where the different phases of thecycle are occurring, the second uses labelling with methyl-[³H]thymidineand autoradiography. Both methods indicate that the endo-S phaseswhich cause the nuclear DNA content to rise from 4C to 8C andfrom 8C to 16C last 8–10 h, and that the intervening endo-Gphase lasts 8–12 h. DNA endoreduplication keeps pace withthe increase of nuclear volume; cell volume increases at a morerapid rate, however. Comparison of the endoreduplication cyclein the metaxylem with the mitotic cycle in the adjoining filesof parenchyma cells shows that the mitotic cells complete theircycle more slowly. DNA synthesis, endoreduplication cycle, mitotic cycle, root apex, Zea mays     

Elastic moduli of excised constricted rat lungs

When airways constrict, the surrounding parenchyma undergoesstretch and distortion. Because of the mechanical interdependence between airways and parenchyma, the material properties of the parenchyma are important factors that modulate the degree ofbronchoconstriction. The purpose of this study was to investigate theeffect of changes in transpulmonary pressure (Ptp) and inducedconstriction on parenchymal bulk (k)and shear (µ) moduli. In excised rat lungs, pressure was measured atthe airway opening, and pressure-volume curves were obtained byimposing step decreases in volume with a calibrated syringe from totallung inflation. Calculation was made ofk during small-volume oscillations (1 Hz). Absolute lung volume at 0 cmH₂O Ptp was obtained bysaline displacement. To calculate µ, a lung-indentation test wasperformed. The lung surface was deformed with a cylindrical punch(diameter = 0.45 cm) in 0.25-mm increments, and the force required toeffect this displacement was measured by a weight balance. Measurementsof k and µ were obtained at 4 and 10 cmH₂O Ptp, and again at 4 cmH₂O Ptp, after delivery ofmethacholine aerosol (100 mg/ml) into the trachea. Values ofk and µ in rat lungs were similar tothose reported in other species. In addition, k and µ were dependent on Ptp. Afterinduced constriction, k and µ increased significantly. That k and µ can increase after induced constriction has important implicationsvis a vis the factors modulating airway narrowing.

     

Cellular pathway of photosynthate transport in coats of developing seed of Vicia faba L. and Phaseolus vulgaris L. I. Extent of transport through the coat symplast

The extent of post-phloem solute transport through the coatsymplasts of developing seeds of Vicia faba L. and Phaseolusvulgaris L. was evaluated. For Vicia seed coats, the membrane-impermeantfluorochrome, CF, moved radially from the chalazal vein to reachthe chlorenchyma and thin-walled parenchyma transfer cell layers.Thereafter, the fluorochrome moved laterally in these two celllayers around the entire circumference of the seed coat. Transferof CF from the chalazal vein was inhibited by plasmolysis ofattached ‘empty’ seed coats. In contrast, the spreadof phloem imported CF was restricted to the ground parenchymaof Phaseolus seed coats. Fluorochrome loaded into the outermostground parenchyma cell layer was rendered immobile followingplasmolysis of excised seed-coat halves. Phloem-imported [¹⁴C]sucroseand the slowly membrane permeable sugar, L-[¹⁴C]glucose, werepartitioned identically between the vascular and non-vascularregions of intact Vicia seed coats. For ¹⁴C-photosynthates,these partitioning patterns in attached ‘empty’Vicia seed coats were unaffected by PCMBS, but inhibited byplasmolysis. Tissue autoradiographs of intact Phaseolus seedcoats demonstrated that a pulse of ¹⁴C-photosynthate moved fromthe veins to the grounds tissues. In excised Vicia seed coats,preloaded with ¹⁴C-photosynthates, the cellular distributionof residual ¹⁴C-label was unaffected by PCMBS. In contrast,PCMBS caused the ¹⁴C-photosynthate levels to be elevated inthe veins and ground parenchyma relative to the branch parenchymaof Phaseolusseed coat halves. Based on the above findings, itis concluded that the phloem of Vicia seed coats is interconnectedto two major symplastic domains; one comprises the chlorenchyma,the other the thin-walled parenchyma plus thin-walled parenchymatransfer cells. For Phaseolusseed coats, the phloem forms amajor symplastic domain with the ground parenchyma. Key words: Phaseolus vulgaris L, phloem unloading, photosynthate transport, seed coat, symplast, Vicia faba L     

Somatic Embryogenesis and Plant Regeneration from Suspension Cultures of Pearl Millet (Pennisetum americanum)

Immature embryos of Pennisetum americanum (pearl millet), culturedin the presence of 2,4-dichlorophenoxy acetic acid (2,4-D) produceda pale-yellow and compact callus tissue by proliferation ofthe scutellum. Teased pieces of the compact callus were placedin a liquid medium on a gyrotory shaker to establish suspensioncultures. The cultures were composed of large, elongated andhigly vacuolated cells, and a population of richly cytoplasmiccells. The latter, here termed embryogenic cells, containednumerous plastids with starch, and occurred in tight groupsof four or more cells, and occasionally as single cells. Structuresresembling various stages of embryogenic development were foundin the suspension cultures. When the cultures were plated ina 2,4-D-free agar medium containing abscisic acid, embryoidswith the typical organization of cereal embryos were produced.The embryoids ‘germinated’ in vitro to give riseto plantlets, which were successfully transferred to soil. Theregenerated plants showed the normal diploid chromosome numberof 14. Embryoids apparently arose from single embryogenic cells,either directly or after the formation of a proembryonal massof cells. embryogenesis, pearl millet, Pennisetum americanum, regeneration, suspension culture