Aerenchyma develops by cell lysis in roots AND CELL SEPARATION IN LEAF PETIOLES IN Sagittaria lancifolia (Alismataceae)

Aerenchyma gas spaces are important for plants that survive flooding because these spaces provide an internal pathway for oxygen transport to the root zone. The objective of this study was to characterize the development of aerenchyma gas spaces in Sagittaria lancifolia L., a dominant species in freshwater wetlands adjacent to the Gulf of Mexico. Tissue at different developmental stages was collected from hydroponically grown plants, embedded in plastic, and sections were observed with a light microscope. In S. lancifolia roots, lysigeny (cell lysis) produced gas spaces that increased in volume from the root meristem to the most mature root tissue. Shoot aerenchyma occurred in the large petioles of S. lancifolia and through the blade midrib, but not in the laminar portion of the blade. In contrast to the roots, gas spaces in the petiole were formed by schizogeny (cell separation during development). Shoot initials produced cells that formed interlocking cylinders in the cortex and diaphragm cells that bridged the central portion of the cylinders. Division and expansion of both these cell types increased the diameter of the cylinders and created schizogenous gaps between diaphragm layers that produced large gas spaces in mature tissue. Therefore, aerenchyma development occurs by two different processes in S. lancifolia.     

Patterns of Distribution of Lateral Root Primordia

The distribution of lateral root primordia has been examinedin Pistia stratiotes and Potentilla palustris, and re-examinedin Pontederia cordata. The major feature of the distributionpattern is a rather regular spacing along protoxylem-based ranks.There appears to be some correlation of activity between ranks,but simulations of patterns based on the data from Pontederiasuggest that the observed correlation is spurious. Pistia stratiotes, Pontederia cordata, Potentilla palustris, roots, lateral roots, pattern     

Structure and Function in the Grass Ligule: Optical and Electron Microscopy of the Membranous Ligule of Lolium temulentum L.

Aspects of the structure and ultrastructure of the membranousligule of mature leaves of Lolium temulentum L. are described.In transverse section the ligule was lens-shaped and wedge-shapedin longitudinal section, 6 or 7 cells wide near the base and1 or 2 cells wide at the edges. Two uniseriate epidermes encloseda chlorenchymatous mesophyll tissue of varying thicknesses;both epidermes were continuous with the leaf adaxial epidermis.The cells comprising these three issues all appeared like typicalgrass epidermal long cells; elongate papillate cells were presentat the edges. No stomata, trichomes, intercellular spaces orvascular tissue were found in the ligule. A marked polarizationof ultrastructural complexity existed from the large-vacuolateabaxial epidermis to the ‘densely cytoplasmic’ small-vacuolateadaxial epidermis. Cells of the latter tissue contained numerousmitochondria, hypersecretory dictyosomes and abundant strandsof rough endoplasmic reticulum. Fluorescence microscopy providedevidence for the accumulation of a polysaccharide-containingmaterial within the periplasmic space next to the outer tangentialwall of adaxial epidermal cells. The ligule is considered tobe a highly organized and differentiated leaf organ with a pholosyntheticmesophyll and an adaxial epidermis active in the synthesis ofprotein and polysaccharide. Darnel, fluorescence microscopy, ligule, Lolium temulentum L., Poaceae, ultrastructure     

Gas and Liquids in Intercellular Spaces of Maize Roots

Oils are spontaneously absorbed by gas-filled intercellularspaces (IS) in maize root cortex. The network of these spacesin living root sections was imaged by confocal laser scanningmicroscopy using a fluorescent solution of Nile red in oil.The gas volume fraction (GVF) of root segments was quantifiedby the increase in weight (differentiated zones) or tissue density(2–3 mm root tips) due to complete vacuum infiltration.Cooling to 6 °C or inhibition of oxidative phosphorylationdiminished the GVF of root tips but did not significantly affectthe GVF of differentiated root zones. The threshold pressuredifference for measurable infiltration of isolated root segmentsis lower (10 to 15  kPa) than the threshold for infiltrationof comparable zones of attached roots or of detached roots withthe cut surface sealed (>60 kPa). In the absence of an opencut, pressure-driven infiltration of the root cortex is acceleratedby microscopic fissures within the epidermal/hypodermal barrier.The GVF of the root cortex was reduced after transferring rootsfrom sugar solutions (0.1 to 0.3M ) to water. This points toefficient water transport from the medium to sugar-containingcortical cell walls through epidermal and hypodermal protoplasts.When 2-cm-long primary roots were vacuum infiltrated in situand then allowed to grow on aerated mineral medium for a further5 d, cortical IS of the originally infiltrated root bases remainedfilled with liquid but the subsequently grown apical root zoneshad a normal GVF. Copyright 1999 Annals of Botany Company Apoplastic and protoplasmic route, maize, infiltration, intercellular spaces, oil absorption, confocal laser scanning microscope, water transport, Zea mays L.     

High pH Causes Disintegration of the Root Surface in Lupinus angustifolius L.

The effect of high pH on the morphology and anatomy of the rootsof lupin (Lupinus angustifolius L. cv. Yandee) and pea (Pisumsativum L. cv. Dundale) was examined in buffered solution. Themorphology and anatomy of lupin roots were markedly altered,and root growth was reduced by increasing solution pH from 5·2to 7·5, whereas pea roots were unaffected. In lupin roots,pH 7·5 caused disintegration of the root surface andimpaired root hair formation. Lupin roots grown at pH 7·5also had decreased cell lengths but increased cell diameterin both the epidermis and the cortex in comparison to rootsgrown at pH 5·2. High pH reduced cell volume greatlyin the epidermis, to a lesser extent in the outer cortex andnot at all in the inner cortex. It appears that in lupins, theprimary detrimental effects of growth at pH 7·5 is reducedlongitudinal growth of cells near the root surface with a consequentreduction in elongation of the cells in inner cortex.Copyright1993, 1999 Academic Press Lupinus angustifolius L., Pisum sativum L., high pH, root morphology, root anatomy     

A Possible Role for the Thick-walled Epidermal Cells in the Mycorrhizal Hair Roots of Lysinema ciliatum R. Br. and other Epacridaceae

Hair roots ofLysinema ciliatum R. Br. and some other Epacridaceaehave thick-walled cells in the epidermis. These are preferentiallycolonized with mycorrhizal fungi. Individual epidermal cellscontaining hyphal coils separate at the middle lamella and arereleased into the soil. Other colonized cells remain attachedto the roots, usually in groups, surrounded by bare exodermis,where epidermal cells have either collapsed or been sloughedoff. It is suggested that these colonized thick walled cellscan serve to prolong the mycorrhizal association and to infectnew hair roots as these emerge. The thick wall has a very specializedstructure and composition and could have a number of roles,either acting as a substrate or protective coat or in controllingwater status and uptake. Young hair-roots are surrounded bya mucilage sheath that is similar in appearance to that in Ericaceaeand apparently produced by root cap cells, not the epidermis. Lysinema ciliatum R. Br.; ericoid mycorrhiza; hair root; root cap; cortex; epidermis; exodermis     

Origin of Epidermis and Development of Root Primordia in Pistia, Hydrocharis and Eichhornia

All three floating plants have roots bearing laterals derivedfrom both pericycle and endodermis. In Pistia and Eichhornialaterals arise within the meristem of the mother root; in Hydrocharisthey arise from mature tissue. In Pistia and Hydrocharis theepidermis becomes anatomically discrete between cortex and cap:in Pistia it is derived from the endodermis of the mother root,in Hydrocharis from the pericycle. The epidermis is not discretein Eichhornia and is derived from the pericycle of the motherroot with the cortex. Stathmokinetic data were used to construct timetables of developmentwhich show how the differences arise. In Pistia the first periclinaldivision of the endodermis-derived tissue individualizes theepidermis and occurs early, before a quiescent centre forms.In Hydrocharis the epidermis also becomes discrete before thepole of the meristem becomes quiescent, but it does so by apericlinal division of the pericycle-derived tissue. In Eichhorniapericlinal divisions occur in the outermost layer of the pericycle-derivedtissue long after quiescence has set in at the pole and afterthe fourth periclinal division in the endodermis derived cap.Its epidermis therefore never becomes anatomically discretethough it becomes functionally discrete because its polar cellsstop dividing as in the other plants. The involvement of the endodermis of mother roots in the formationof laterals is discussed in relation to the state of differentiationat sites of primordium formation, discreteness of the epidermisand subsequent fate of primordia. Pistia stratiotes L., Hydrocharis morsus-ranae L., Eichhornia crassipes Solms., primordia, lateral root, discrete epidermis, development, chimera, stathmokinetics     

Interaction between rhizobia and potato tissues10

Several cultivars of Solanum tuberosum L., the potato, weregrown on tissue culture media and their roots inoculated withstrains of rhizobia known to infect legumes at root junctionsor between epidermal cells. Infection incidence and severityshowed considerable cultivar/bacterial strain interaction. Bacteriaspread through intercellular spaces and invaded cells in a non-structuredway: some infections penetrated to the root xylem. There wasno evidence that potato root cells produced nod-inducing factorsand nitrogenase activity was not detected. In some host/rhizobialcombinations outgrowths were formed on roots. These varied fromloose infected callus tissue at the junctions of lateral roots,to modified lateral roots of limited growth which showed somecolonization by rhizobia. Key words: Solarium tuberosum L, potato, glycoprotein, immunogold labelling, rhizobia, flavonoids     

Arrangement of Cortical Microtubules in Avena Coleoptiles and Mesocotyls and Pisum Epicotyls

Cortical microtubules (MTs) in coleoptiles and mesocotyls ofAvena sativa and epicotyls of Pisum sativum were examined byimmunofluorescence. In elongating Avena coleoptiles whose elongationis less localized, the orientations of cortical MTs of parenchymaand adaxial epidermal cells, and abaxial epidermal cells aretransverse, and oblique or longitudinal, respectively, and doesnot differ between the upper, middle and lower parts. The transverseMTs in parenchyma and adaxial epidermal cells turns to obliqueor longitudinal ones after elongation stops. The obliquity ofMTs in abaxial epidermal cells also tends to become steeperas elongation comes to a stop. In Avena mesocotyls and Pisumepicotyls whose elongation is localized, the orientation ofcortical MTs of cortical cells in the elongating region is relativelytransverse. The epidermis has intermingling cells of transverseor oblique MTs. In the non-elongating region, MT orientationbecomes steeper both in the cortex and epidermis. The present results indicate that whatever the degree of localizationof the elongation, the obliquity of MTs in these organs is steeperin epidermal than in inner tissue cells and becomes steeperas elongation stops in both tissues. (Received October 26, 1987; Accepted April 19, 1988)     

Ultrastructural and physiological changes in root cells of Sorghum plants (Sorghum bicolor S. sudanensis cv. Sweet Sioux) induced by NaCl

The xerophytic, but salt-sensitive Sorghum cultivar ‘SweetSioux’ is known as an ion excluder with a high K/Na selectivityat the plasmalemma and tonoplast of epidermal root cells. Theaim of this study is the correlation of salt-effected changesin physiological parameters with structural and ultrastructuralchanges in root cells. The investigation was carried out withroot cells because these cells are most directly exposed tothe growth medium. Sorghum bicolor S. sudanensis cv. Sweet Sioux plants weregrown under steady-state conditions on nutrient solutions withor without 40 mol m^–3 NaCl. Sorghum sustained this treatmentbut showed several salt-induced structural and physiologicalchanges which were studied in various cell types of the roottip. (1) NaCl salinity led to a shorter growth region and to salt-inducedalterations in the chemical and physical properties of the cellwalls in the root tips. (2) Salt treatment also increased the membrane surface in rootcells: root cells showed an increase in the quantity of vesiclesin the epidermis and in the middle cortex cells. Additionally,some of the epidermis cells of salt-treated plants revealeda characteristic build-up of transfer cells, suggesting an increasein membrane surfaces to increase the uptake and storage of substances. (3) The number of mitochondria increased in the epidermal andin the cortex cells after salt stress thus indicating an additionalsupply of energy for osmotic adaptation and for selective uptakeand transport processes. (4) In the epidermal cytoplasm NaCl stress led to a significantdecrease of the P, K, Ca, and S concentrations accompanied byan increase of Na concentration. Electron micrographs show anincrease in electron optical contrast within the cytosol andin the matrix of the mitochondria. These results are discussedwith regard to the possibility of influence on the part of metabolicfunctions. (5) The NaCl concentrations were seen to increase and the Kconcentrations to decrease during salt stress in the vacuolesof the epidermis and cortex cells. The salt-induced increasein vacuolar NaCl concentrations of epidermis and cortex cellsare in the region 2 cm behind the root tip, which is sufficientfor an osmotic balance towards the growth medium. Additionalsolutes are necessary 0.5 mm behind the root tip to facilitateosmotic adaptation. The results show ultrastructural changes caused by an Na-avoidingmechanism characterized by a high level of energy consumption.The exclusion of Na from the symplast seems to lead additionallyto a decrease in cytoplasmic concentrations of such essentialelements as Mg, P, S, and Ca and is thus responsible directly(via energy supply in mitochondria, homeostasis, selectivityof K over Na) or indirectly (via enzyme conformation, cytoplasmichydration) for the ultra-structural degradation indicated. Thesalinity-induced multiplicity of structural and functional changeswithin cell compartments constitutes a group of indicators forthe limited NaCl tolerance of Sorghum. Key words: Sorghum bicolor S. sudanensis, ultrastructure, salt tolerance, NaCl, Ca-deficiency     

Variation in expression of trimorphic incompatibility in Pontederia cordata L. (Pontederiaceae)

Summary Pontederia cordata L. (Pontederiaceae), a perennial diploid, possesses the rare genetic polymorphism tristyly. A controlled pollination programme was conducted over a three year period, under glasshouse conditions, on 36 clones of P. cordata var. cordata to examine the nature of the self-incompatibility system. The three major findings of the pollination study were: (1) the three floral morphs display different levels of self-incompatibility, (2) pollen from the two anther levels within a flower exhibits different compatibility behaviour in self-pollinations, (3) considerable individual genetic variation in the expression of self-incompatibility is evident among clones within floral morphs. Similar results were also obtained from a smaller study on 15 clones of P. cordata var. lancifolia conducted over a 6 month period. In common with other Pontederia species the mid-styled morph (M) of P. cordata produces large amounts of seed when self-pollinated with pollen from long-level anthers. A developmental model is proposed to explain the high level of self-compatibility of the M morph in Pontederia species. Self-pollination of segregating progenies from M and S morphs of known incompatibility status demonstrated that the expression of incompatibility is closely associated with style length. It is suggested that overall differences in incompatibility behaviour among the floral morphs may be due to the pleiotropic effects of major genes controlling sub-characters of the tristylous syndrome, rather than linked modifier genes. However, the variable expression of trimorphic incompatibility within floral morphs suggests that this variation may be polygenic in origin.     

Infection and Root-Nodule Development in Stylosanthes Species by Rhizobium

Root nodules of the tropical forage legume Stylosanthes occurredonly at lateral root junctions and resulted from direct invasionby rhizobia through spaces between epidermal cells. No infectionthreads were present in either the root hairs or nodules. Invasionof the host cortical cells was through structurally alteredcell walls. The bacteria reached the site of nodule initiationin the lateral root cortex by progressive collapse of the initiallyinvaded cells which were compressed by neighbouring cells toform intercellular thread-like infection zones. The bacteriamultiplied in the invaded cells of the nodule initial whichdivided repeatedly to form the nodule. Bacteroids formed onlywhen the host cells ceased to divide. Some abnormal associations occurred in S. capltata and S. hamata40264A. Division of invaded cells was restricted in S. capitataand the bacteria became enlarged and grossly deformed. In S.hamata restricted cell division was immediastely followed bythe brcakdown of the host cells and, although the bacteria multiplied,no bacteroids were formed. Bacteria isolated from these nodulesformed both effective and abnormal nodules when inoculated ontothe same host.     

Histological changes in guava root during wilting induced by Fusarium spp.

Wilt is the most destructive disease of guava in India. Fusarium oxysporum f. sp. psidii and Fusarium solani are reported as most commonly isolated pathogens and are considered to be associated singly or in combination with roots of wilt affected plants of guava (Psidium guajava L.). Histopathological observations were made of the roots of wilt affected guava plants in the present investigation. The observations of wilted guava root showed disintegration/necrosis of the epidermal tissue, cortex tissue and vascular bundle cells. In T.S. of root of wilted plant the normal shape of the epidermis was disrupted and there was breaking and opening in the epidermis through which pathogen may enter in the host tissue. Necrosis of the internal tissue and vascular bundle restricts the movement of water and nutrient and thus results wilting.     

Effect of Ferricyanide on Potassium Uptake by Intact Epidermal Tissue and Guard Cell Protoplasts

The effect of ferricyanide on K^$ fluxes in epidermis and inguard cells of Commelina communis L. were studied. Ferricyanideenhanced guard cell protoplasts swelling, which results fromenhanced K^$ uptake. In intact epidermis ferricyanide inhibitedK^$ uptake and consequently, stomatal opening. This was foundin floated and submerged epidermal tissues, indicating thatthe degree of contact with the solution does not affect theresponse to ferricyanide. Investigation of the rate of plasmolysisand de-plasmolysis of guard cells in epidermal tissue revealedthat ferricyanide enhances deplasmolysis, caused by K^$ uptake,only in completely plasmolysed cells, which resemble protoplastsin situ. (Received January 21, 1988; Accepted March 24, 1988)     

Anatomy and Histochemistry of the Root System of the Kiwifruit Vine, Actinidia deliciosa var. deliciosa.

The kiwifruit vine is a species which has been newly introducedinto cultivation and little is known of its comparative physiologyand anatomy. In this study we found that fibrous, 'magnolioid'roots, which have undergone secondary vascular development butwhich retain the cortex and develop a suberized epidermis, comprisethe greater part of the root system (95% of total length). Newlyinitiated roots with primary development conform to norms establishedin other woody plant species. However, the structural roots,like the fibrous roots, also retain a cortex and phellodermwhich is initiated by hypodermal cells within the cortex andnot by the pericycle which is the common progenitor tissue inother species. This phellogen produces new cells centrifugallyonly. The cortex is a relatively small component of the structuralroot and the bulk of the tissue is vascular in origin, as inthe roots of other plant species. The endodermis is retainedand continues to divide periclinally to accommodate the increasein circumference with growth.Copyright 1993, 1999 Academic Press Actinidia deliciosa, root anatomy, ontogony, histochemistry, exodermis, endodermis     

Stomatal Pattern in Four Species of Monocotyledons

The distribution of stomata has been investigated in the leafepidermis of Chlorophytum comosum, Galanthus nivalis, Schizostyliscoccinea and Scilla lancifolia. The epidermis was consideredto consist of units of construction of two kinds: type A, along epidermal cell with a stoma at its distal end, and typeB, a long epidermal cell without an associated stoma. Exceptin Scilla, the probability of an epidermal unit being type Aincreases approximately with its length. Considering the epidermisas rows of units, alternating sequences of type A and type Bdo not occur randomly along the rows. In Chlorophytum, Galanthusand Schizostylis, both type A and B units tend to be aggregatedinto longer sequences than would be expected on a random basis.It is suggested that homoeogenetic induction (i.e. of like bylike) may be occurring during development. No case can be madefor homoeogenetic induction of units in Scilla. There is a slighttendency to periodicity of distribution of type A units in Galanthus,Schizostylis and Scilla, but this does not seem to representa primary element of pattern. There is interaction between rowsin the sense that unit ends (transverse walls) tend to avoidthose in neighbour rows; this affects the relative distributionof stomata, but there is no evidence of any direct interactionbetween stomata in different rows. Chlorophytum comosum, Galanthus nivalis, Schizostylis coccinea, Scilla lancifolia, leaf, epidermis, stomata, pattern     

The Structure of Nitrogen Fixing Root Nodules on the Aquatic Mimosoid Legume Neptunia plena

Nodules of the aquatic mimosoid legume Neptunia plena (L.) Benth.were always found associated with roots but not stems. Theyappeared macroscopically 10 and 20 d after inoculation on plantsgrown hydroponically and in vermiculite, respectively. The developmentof nitrogen-fixing cells occurred in a series of stages notyet reported in legume nodule formation: initial infection wasapparently intercellular and rhizobia spread between cells andthrough intercellular spaces before penetrating individual hostcells by means of infection threads. Subsequently nodule developmentwas broadly similar to that described for indeterminate papilionoidnodules. The infection threads of Neptunia and pea nodules containeda matrix with a common epitope, which was, in Neptunia, extrudedfrom the infection thread at the point of bacterial release. The central tissue contained infected and interstitial cellsand was surrounded by a three-layered cortex and a phellem.Bounding the infected region was a layer two to three cellsthick with large, unoccluded intercellular spaces. Externalto this was a layer, one or more cells thick, in which the cellwalls were interlocked, reducing the number of radially orientedintercellular spaces. The outer layer, several cells thick,contained intercellular spaces many of which were occluded.These features did not vary with growth conditions in a waywhich might influence oxygen diffusion characteristics. However,the phellem of water-cultured nodules was much more aerenchymatousthan that of vermiculite-grown nodules. Aquatic legume, Neptunia plena, nitrogen fixation, oxygen, root nodules, Rhizobium     

Variant restoration trajectories for wetland plant communities on a channelized floodplain

Restoration efforts are typically based on an assumption that reestablishment of altered determinants of ecological structure and function will lead to a predictable reestablishment of populations and reassembly of communities. Dechannelization and reestablishment of natural hydrologic regimes provide the basis for the ongoing restoration of the Kissimmee River in Central Florida, United States. The expected reestablishment of historically dominant broadleaf marsh (BLM) and buttonbush shrub (BB) communities was evaluated over a 10‐year period following implementation of the first phase of the restoration project. Plant species composition and cover were assessed during dry (spring) and wet (summer) season sampling periods at five sites on the restored floodplain, and four “control” sites on the channelized floodplain. Mean daily stage data from nearby gauges indicated hydroperiods and depths on the reflooded floodplain were within the range of historic hydrologic conditions that selected for BLM and BB communities on the pre‐channelization floodplain. After reflooding, pasture grass and upland shrub communities rapidly transitioned to a fluid mix of obligate and facultative wetland species. Although signature BLM and BB species, Sagittaria lancifolia (bulltongue arrowhead), Pontederia cordata (pickerel weed), and Cephalanthus occidentalis (buttonbush), recolonized all study sites, the expected reestablishment of dominant cover of these species did not occur. Results indicate that restoration of BLM and BB communities has been impeded by deep flood pulse disturbances, establishment of invasive wetland grasses, and mineralized soil characteristics of the drained floodplain.     

Salinity as a constraint on growth of oligohaline marsh macrophytes. I. Species variation in stress tolerance

The effects of increased salinity on plant growth were examined in a greenhouse experiment with four species common to oligohaline marshes of the northern Gulf of Mexico: Eleocharis palustris, Panicum hemitomon, Sagittaria lancifolia, and Scirpus americanus. Effects of final salinity reached (6 or 12 g/L), salinity influx rate (3 d or 3 wk), and duration of exposure (1, 2, or 3 mo) were investigated. Sagittaria lancifolia was the first species to show visible signs of stress, with browning and curling of older leaf edges. The salt effect was delayed for 6-8 wk in P. hemitomon, but this species had the highest aboveground tissue mortality rate at 12 g/L as exposure continued. Final salt concentration affected all species to a greater degree than did salinity influx rate. No aboveground mortality occurred at 6 g/L, but growth suppression was apparent and varied with species. The magnitude of growth suppression in response to salinity increased for all species as the duration of exposure increased. Overall, we ranked the species as follows, in order from least to most salt tolerant: Panicum hemitomon < Sagittaria lancifolia < Eleocharis palustris < Scirpus americanus. This ranking reflects the field occurrence of these species along a gradient of increasing salinity in northern Gulf of Mexico coastal habitats from freshwater wetlands through oligohaline areas to mesohaline wetlands.