Further Observations on Root Contraction

Further observations, by light and electron microscopy, on theanatomy of root contraction in Hyacinthus orientalis cvs. arereported, together with some comparisons with Narcissus andGladiolus. It is maintained that root contraction in these andsome other species is essentially a growth process, as previousinvestigators have shown, and that an understanding of the re-directedgrowth of the cortical cells which brings it about may be basedon the specialized structural features of their cell walls,here described. Physical, anatomical and comparative reasonsare given for our belief that the alternative explanation ofthe contractile process in Gladiolus which relates it to cellcollapse resulting from transpirational ‘pull’ isuntenable. anatomy, contraction, Hyacinthus, Narcissus, Gladiolus, root     

The Penetration of Solar Radiation through Leaf Canopies of Different Structure

A comparative study has been made of the penetration of solarradiation through leaf canopies of contrasting structure. Forthis purpose experiments were undertaken on (a) Gladiolus withnearly vertical leaves, (b) Raphanus sativus with its rosettehabit, (c) two varieties of Linum usitatissimum, one an unbranchedflax type and the other a multi-stem linseed type, and (d) Agrostemmagithago where the apical leaves are sharply inclined and thebasal leaves disposed in a horizontal plane. Light gradientswere evaluated at different densities and at varying stagesof development by means of probes of silicon cells. Using afilter (cut off point 72-5 µ) simultaneous measurementswere made of the infra-red and ‘visible’ radiation.The distributions of the leaf and stem area through the canopywere recorded so that light interception per unit surface couldbe assessed. The shape of the light gradient between the top and bottom ofthe canopy was sigmoidal for Gladiolus but much less so forthe other species. Attenuation of the infra-red radiation withdepth was markedly smaller. For valid estimates of the extinction coefficient (K) it isessential to include stem areas; that is on theoretical groundshalf the total stem surface. The values of K were low for allspecies and in particular for Gladiolus. The relationship betweenlight attenuation and leaf area was approximately exponential.For Gladiolus it was established that K can decrease with increasingdensity but no changes with depth in the canopy were evident.The implications of these observations in terms of canopy structureare discussed.     

Pollination and Pollen-pistil Interaction in Oil Palm, Elaeis guineensis

Structural and cytochemical aspects of the pistil and detailsof pollination and pollen-pistil interaction were investigatedin the African oil palm (Elaeis guineensis Jacq.), an importantperennial oil crop. The stigma is trilobed, wet and papillate.The branched papillae are confined to a narrow linear zone oneach stigmatic lobe. Each stigmatic lobe harbours a deep stigmaticgroove, which runs adaxially along the surface. The stigmaticgroove is bordered by a well-defined layer of glandular cells,each of which has a pectinaceous cap on the inner tangentialwall. The style is hollow. The canal cells show thickeningson the inner tangential wall. The stigmatic groove and stylarcanal contain an extracellular matrix secreted by the canalcells which is rich in proteins, acidic polysaccharides andpectins. The canal cells at the base of the style are papillateand loosely fill the stylar canal. The stigma becomes receptivewhen the stigmatic lobes separate, and remains so for 24 h.Pollination is mediated by weevils as well as by the wind. Undernatural conditions the pollination efficiency was 100%. Pollinationinduces additional secretion in the stigmatic groove and stylarcanal. During post-pollination secretion, the pectinaceous capsof the cells lining the stigmatic groove are degraded. Pollengrains germinate on the stigmatic papillae and tubes grow onthe surface of the papillae, entering the stigmatic groove andadvancing along it into the stylar canal to eventually gainaccess to the locules. Pollen tubes are seen in the ovules 18–20h after pollination. Copyright 2001 Annals of Botany Company Arecaceae, Elaeis guineensis, African oil palm, pollination, stigmatic grove, stylar canal, Tenera hybrid, weevil     

Structural and Cytochemical Analysis of the Stigma and Style in Tibouchina semidecandra Cogn. (Melastomataceae)

Structural and cytochemical aspects of the pistil of Tibouchinasemidecandra Cogn. were studied. The stigma is of the wet-papillatetype and is structurally divisible into a papillar zone anda stigmatic zone. The papillar zone consists of loosely arrangedpapillae which are matchstick-shaped, unicellular, and producelipid droplets that remain entrapped below the thick cuticle.The bulk of cell volume is made up of large vacuoles rich intannin. The stigmatic zone consists of layers of secretory cellswith dense cytoplasm, actively secreting dictyosomes and numerousrough endoplasmic reticulum (RER) profiles. Free-flowing lipidexudate, produced by these cells, is initially stored in theintercellular spaces, and subsequently extruded out to coverthe surface. The style is solid with a core of transmittingtissue traversing its whole length. The transmitting tissueconsists of loosely arranged cells with numerous organellesand conspicuous intercellular substance rich in polysaccharidesand pectins. Ultrastructural details indicate that the intercellularsecretion is accompanied with fraying of the wall component.Both the transverse and longitudinal walls contain plasmodesmata.Copyright1995, 1999 Academic Press Cytochemistry, stigma and style, ultrastructure, Tibouchina semidecandra     

The Anatomy, Histochemistry and Ultrastructure of Stigmas and Styles in Commelinaceae

The anatomy and ultrastructure of stigmas in 37 species of 13genera of Commelinaceae are described. The stigmas are papillate,papillae forming a dense fringe of cells around the mouth ofthe stylar canal in most species. The papillar cell wall iscovered by an unstructured cuticle of variable thickness andis of variable thickness because of small wall ingrowths. Thecuticle and the external surface of the papillar cell wall arevariably disrupted, particularly in the mid and basal regionsof the cell. This was not found in species of the genus Aploleiaor Callisia. The cell cytoplasm possesses all major organellesexcept chloroplasts and each cell is vacuolate. In all species except Aploleia mulitiflora the style comprisesan epidermis, a cortex and a hollow, tripartite canal whichis continuous into the ovary cavity. The three vascular strandsare positioned at the apex of each canal lobe. The canal cellsare elongate and tabular and the wall abutting the canal hasingrowths. The style in Aploleia is solid and the transmittingtissue comprises cells whose walls are electron opaque. Thecytoplasms of both types of cell are similar in content althoughthere is a single, large vacuole in canal cells and many smallvacuoles in transmitting tissue. The morphology, position and histochemistry of stigmatic andstylar exudate was similar in all ‘wet’ stigmas.Most of the exudate originates from the stylar canal althoughsignificant contributions are made by the papillae in stigmasof Coleotrype, Dichorisandra and Thyrsanthemum. There is no apparent relationship between stigma structure andthe presence of self-incompatibility. Stigma papillae, stylar canal, transmitting tissue, Commelinaceae     

Sugars in Natural and Artificial Pollen Germination Substrates

The stigmatic exudates and pollen grains of five unrelated specieswere tested for sugars. Glucose, fructose, and sucrose werefound in the stigmatic fluid of Yucca aloifolia L. and glucoseand fructose in that of Oenothera adrummondii Hook. In in vitroexperiments with Y. aloifolia pollen, high germination percentageswere obtained in artificial media containing glucose or sucrose.Fructose, which is present in the stigmatic fluid of the Yuccasp. resulted in high in vitro pollen germination only when borateand calcium were added to the medium. Presence of bound sugarsis indicated in the stigmatic secretion of Citrus aurantiumL. and pollen of the single plant tested germinated at a lowpercentage in artificial sugar media. No sugars were detectedin the stigmatic fluids of Hemerocallis fulva L. and Zea maysL. and in these two species in vitro pollen germination in sugarymedia was negligible or absent. The pollen grains of all five species contain sucrose and thoseof Oenothera and Citrus also reducing sugars.     

Sap Exudation via the Epidermis of Leaves

Reports of stomatal guttation in Gladiolus and of active waterexudation in Vidafaba could not be confirmed by an experimentaland anatomical investigation. Exudation of water from detachedpine needles is considered to be due to processes distinct fromthose causing guttation. Water soaking of leaves, or the flooding of leaf air spaces,and the wettability of cell walls under root pressure as distinctfrom their wettability by water externally applied are discussedin relation to the experimental results.     

Papillar integrity as an indicator of stigmatic receptivity in kiwifruit (Actinidia deliciosa)

Stigmatic receptivity is a major factor limiting fruit set inkiwifruit (Actinidia deliciosa). The aim of this work was toknow what determines the cessation of stigmatic receptivityin this species. Stigmatic receptivity has been analysed inkiwifruit through the capacity of the stigma to sustain pollengermination and has been related to stigmatic development anddegeneration.The stigma of kiwifruit flowers has a papillatesurface which from anthesis is covered with an abundant exudate.Papillae are unicellular and contain a number of phenolic deposits.During the lifetime of the flower these papillae gradually loseturgidity, while stigmatic secretion increases until 5 d afteranthesis when papillae start rupturing and the papillar contentis liberated into the germination medium. Stigmatic receptivityis high at anthesis and lasts for the next 4 d. However, itdrastically decreases 5 d after anthesis and it is nil 2 d later.The pattern of stigmatic receptivity closely fits that of papillarintegrity, indicating that stigmatic receptivity relies on thisintegrity. Since papillar integrity can easily be evaluatedin stigmatic arms, this criterion can be used as a quick methodto estimate stigmatic receptivity. Key words: Actinidia deliciosa, kiwifruit, stigma, receptivity, pollen     

Relative Sensitivity and Tolerance of some Gladiolus Cultivars to Sulphur Dioxide

Five Gladiolus cultivars, namely ‘Aldebaran’, ‘BrightEye’, ‘Illusion’, ‘Manisha’ and‘Manmohan’, were exposed to 1 and 2 µg l^–1sulphur dioxide to test their relative-sensitivity toleranceto the pollutant Plants were fumigated experimentally for 2h daily Foliar injury symptoms were observed first in ‘Manisha’followed by ‘Aldebaran’ and ‘Illusion’at the higher dose Photosynthetic pigments and leaf extractpH were significantly decreased, particularly in ‘Manisha’and ‘Illusion’ Overall disturbances in the plantmetabolism due to SO₂ treatment led to retarded growth of plants,as evident from decreased shoot length and phytomass valuesThe order of sensitivity of the five Gladiolus cultivars toSO₂ was as follows, with the greatest first Manisha, Illusion,Aldebaran, Bright Eye, Manmohan Cultivars, Gladiolus, sensitivity, sulphur dioxide, tolerance     

Nitrate Supply and the Biophysics of Leaf Growth in Salix viminalis

The influence of nitrogen on leaf area development and the biophysicsof leaf growth was studied using clonal plants of the shrubwillow, Salix viminalis grown with either optimal (High N) orsub-optimal (Low N) supplies of nitrate. Leaf growth rate andfinal leaf size were reduced in the sub-optimal treatment andthe data suggest that in young rapidly growing leaves, thiswas primarily due to changes in cell wall properties, sincecell wall extensibility (% plasticity) was reduced in the LowN plants. The biophysical regulation of leaf cell expansion also differedwith nitrogen treatment as leaves aged. In the High N leaves,leaf cell turgor pressure (P) increased with age whilst in theLow N leaves P declined with age, again suggesting that foryoung leaves, cell wall plasticity limited expansion in theLow N plants. Measurements of cell wall properties showed thatcell wall elasticity (%E) was not influenced by nitrogen treatmentand remained constant regardless of leaf age. Key words: Salix, cell wall extensibility, nitrogen nutrition, biophysics of leaf growth     

Contrasting CO2 and temperature effects on leaf growth of perennial ryegrass in spring and summer

The effects of increased atmospheric carbon dioxide (CO₂) of700 µmol mol^–1 and increased air temperature of+ 4C were examined in Lolium perenne L. cv. Vigor, growingin semi-controlled greenhouses. Leaf growth, segmental elongationrates (SER), water relations, cell wall (tensiometric) extensibility(%P) and epidermal cell lengths (ECL) were measured in expandingleaves in spring and summer. In elevated CO₂, shoot dry weight (SDW) increased in mid-summer.In both seasons, SDW decreased in elevated air temperatureswith this reduction being greater in summer as compared to spring.Specific leaf area (SLA) decreased in elevated CO₂ and in CO₂ temperature in both seasons. In spring, increased leaf extensionand SER in elevated CO₂ were linked with increased ECL, %P andfinal leaf size whilst in summer all were reduced. In high temperature,leaf extension, SER, %P and final leaf size were reduced inboth seasons. In elevated CO₂ temperature, leaf extension,SER, %P, and ECL increased in spring, but final leaf size remainedunaltered, whilst in summer all decreased. Mid-morning waterpotential did not differ with CO₂ or temperature treatments.Leaf turgor pressure increased in elevated CO₂ in spring andremained similar to the control in summer whilst solute potentialdecreased in spring and increased in summer. Contrasting seasonalgrowth responses of L. perenne in response to elevated CO₂ andtemperature suggests pasture management may change in the future.The grazing season may be prolonged, but whole season productivitymay become more variable than today. Key words: Lolium perenne, ryegrass, CO₂ and temperature, leaf extension, cell wall rheology     

Development of the Sieve Plate in Saxifraga sarmentosa L.

The differentiating sieve plate in the phloem of the stolonof Saxifraga sarmentosa L. was studied with the electron microscope.Development of the pore site begins with differentiation ofa pair of collar-like areas around the plasmodesma which canbe seen in the youngest identifiable sieve plates. Further growthof the collars occurs by deposition of an amorphous substance,presumably caflose. Although the growth of the collars is simultaneouswith the growth of the surrounding cell wall it is rapid atfirst and the pore sites appear asdome-shaped protuberances.It also involves deposition of callose over an increasinglywider area of the cell wall and since the thickening of thenormal cell wall continues only where notcovered by callose,the collars assume a conical form. There seems to be no displacementor lysis of normal cell wall material during growth of the collars.Eventually the growth of the cell wall in thickness overtakesthe pore sites so that when the growth of the cell wall is completethe pore sites appear as depressions in the sieve plate. Theperforation of a pore site is accomplished by widening of theplasmodesmatal cylinder which begins at the middle lamella byremoval of callose. Endoplasmic reticulum is found in closeproximity to the plasmodesma andis believed to penetrate it.     

Hormonal Regulation of Cormel Formation in Gladiolus Stolons Grown in vitro

The influence of four plant hormones on cormel development inGladiolus stolon tips grown in vitro was tested. Kinetin inducedcormel formation while Gibberellin A₃ inhibited it at low kinetinlevels. Abscisic acid did not affect cormel formation, but inhibitedtheir growth. Naphthalene acetic acid had no direct effect ontuberization. Anatomical observations revealed no differencesbetween cormels formed in vitro and in vivo.     

REABSORPTION OF ORGANIC SOLUTES IN SOME MARINE AND FRESHWATER PROSOBRANCH GASTROPODS

Influx in vitro of glucose to the heart, kidney and ureter,where present, in Monodonta, Pomacea, and Viviparus, and alsoof leucine to these tissues in Viviparus, was measured using[³H]-labelledtracers. Phloridizin-sensitive, Na⁺-dependent [³H]D-glucose uptake wasevident in the papillary sac of Monodonta, the ventricle ofViviparus, and the kidney of Pomacea. Viviparus ventricle alsoshowed Na⁺-dependent uptake of [³H]L-leucine. Nevertheless Viviparusappears to excrete some amino acids (by undefined routes) andmay therefore lack the carriers for their resorption. In Viviparusand Pomacea the site of organic solute resorption (taken tobe where Na⁺-dependent tracer uptake predominates) is proximalto the sites of Na⁺resorption. The ultrastructure of the resorptivesites has been examined in the three genera and compared withthat of the nephridial gland and dorsal wall of the kidney ofLittorina. The ciliated cells comprising the epithelium of thepapillary sac in Monodonta and their homologues over the nephridialgland and dorsal wall of Littorina and dorsal wall of Pomaceashow common features typical of transporting epithelia in othermolluscs. The ventricular epicardium of Viviparus shows secondaryspecializations for resorption but lacks an endocytotic canalsystem. The site of organic solute resorption (the most highlyspecialized part of which is the nephridial gland in marinespecies), has been correlated with the anatomy of the renalveins in the four genera, and with other specializations inthe freshwater genera.The difficulty of quantifying rates oftransport of solutes from studies in vitro is discussed. ^*Present address: Dept. of Physiology, The University, DundeeDD1 4HN (Received 31 January 1989; accepted 24 March 1989)     

Stigmatic Self-Incompatibility and Mating Patterns in Trillium grandiflorum and Trillium erectum(Melanthiaceae)

Post-pollination processes governing mating patterns in Trillium,a well-known genus of insect-pollinated woodland herbs, arepoorly understood. Mechanisms influencing outcrossing were investigatedin T. grandiflorum and T. erectum, two widespread species nativeto eastern North America. In southern Ontario, Canada, the twospecies are often sympatric; they flower in early May, and arepollinated by different assemblages of insects. Controlled cross-and self-pollinations and structural observations of pollengermination and pollen tube growth were conducted to determinewhether the two species possess a self-incompatibility (SI)system and, if so, the specific site(s) of self-rejection. Controlledpollinations indicated that both species set significantly moreseeds from cross-pollination than self-pollination, implicatingthe action of SI. This was confirmed by structural studies whichdemonstrated that self-recognition and rejection reactions occurredon dry-type stigmatic papillae. Observations of pollen hydrationrevealed that self-rejection was rapid, being initiated within10 min of pollination and prior to pollen tube emergence. Finalself-rejection resulted in failure of pollen tube growth atthe base of stigmatic papillae. SI was expressed more weaklyin T. erectum and thereby resulted in considerable self-seedset in some individuals . Estimates of outcrossing rates usingallozyme markers indicated that T. erectum displayed a mixed-matingsystem whereas T. grandiflorum was more highly outcrossed. Structuralstudies of pollen traits indicated that the two species differedwith respect to the size of grains and their aggregation withimplications for pollen dispersal and mating. The ecologicaland evolutionary implications of the variable expression ofSI in Trillium are discussed. Copyright 2001 Annals of BotanyCompany Trillium grandiflorum, Trillium erectum, self-incompatibility, mating     

Effects of cytochrome c on the mitochondrial apoptosis-induced channel MAC

Recent studies indicate that cytochrome c is released early in apoptosis without loss of integrity of the mitochondrial outer membrane in some cell types. The high-conductance mitochondrial apoptosis-induced channel (MAC) forms in the outer membrane early in apoptosis of FL5.12 cells. Physiological (micromolar) levels of cytochrome c alter MAC activity, and these effects are referred to as types 1 and 2. Type 1 effects are consistent with a partitioning of cytochrome c into the pore of MAC and include a modest decrease in conductance that is dose and voltage dependent, reversible, and has an increase in noise. Type 2 effects may correspond to "plugging" of the pore or destabilization of the open state. Type 2 effects are a dose-dependent, voltage-independent, and irreversible decrease in conductance. MAC is a heterogeneous channel with variable conductance. Cytochrome c affects MAC in a pore size-dependent manner, with maximal effects of cytochrome c on MAC with conductance of 1.9–5.4 nS. The effects of cytochrome c, RNase A, and high salt on MAC indicate that size, rather than charge, is crucial. The effects of dextran molecules of various sizes indicate that the pore diameter of MAC is slightly larger than that of 17-kDa dextran, which should be sufficient to allow the passage of 12-kDa cytochrome c. These findings are consistent with the notion that MAC is the pore through which cytochrome c is released from mitochondria during apoptosis. patch clamp; ion channels     

Specificity of Gibberellin and Sucrose-promoted Flower Bud Growth in Gladiolus

A critical stage in flower bud growth in the spike of Gladioluswhich is initiated by gibberellic acid (GA₃) and sustained bysucrose has been identified. This corresponds to the stage atwhich separation of the outer bract occurs. In buds at differentdevelopmental stages isolated and held in water, it is the samebud stage that first shows increased growth. Buds not inducedby light were shown to respond more significantly to GA₃ andsucrose than those induced by light. Since the separation ofthe outer bract results in light-induced amylase productionand starch hydrolysis leading to petal growth, it is proposedthat growth promotion by GA₃ is related to light-induced petalgrowth at this specific stage. flower bud growth, Gladiolus natalensis, gibberellic acid, sucrose     

Cellular Processes Limiting Leaf Growth in Plants under Hypoxic Root Stress

The effects of root hypoxia on leaf growth of a Populus trichocarpa? deltoides hybrid have been assessed. Clonal plants were subjectedto hypoxic root conditions in pot culture by flooding and insolution culture by gassing with nitrogen. The rate of leafexpansion declined within 8 h and was suppressed for the durationof the treatment. Final leaf size was reduced by 35% to 60%compared to aerated plants. Final epidermal cell size and numberdepended both on the developmental stage of the leaf at theonset of stress and on the duration of the treatment. No differencesin bulk leaf water potential were measured between the hypoxicand aerated plants. Cell wall extensibility was lower, leafsolute potential was more negative and turgor potential washigher in leaves of hypoxia-treated plants than of aerated plants.These data suggest that leaf growth of hypoxia-stressed plantsis limited by cell wall extensibility. The mechanism by whichthe root stress induces changes in leaf cell wall characteristicsis not known. Key words: Populus, flooding     

ZmXTH1, a new xyloglucan endotransglucosylase/hydrolase in maize, affects cell wall structure and composition in Arabidopsis thaliana

Xyloglucan endotransglucosylase/hydrolases (XTHs; EC 2.4.1.207and/or EC 3.2.1.15 [EC] 1) are enzymes involved in the modificationof cell wall structure by cleaving and, often, also re-joiningxyloglucan molecules in primary plant cell walls. Using a poolof antibodies raised against an enriched cell wall protein fraction,a new XTH cDNA in maize, ZmXTH1, has been isolated from a cDNAexpression library obtained from the elongation zone of themaize root. The predicted protein has a putative N-terminalsignal peptide and possesses the typical domains of this enzymefamily, such as a catalytic domain that is homologous to thatof Bacillus macerans β-glucanase, a putative N-glycosylationmotif, and four cysteine residues in the central and C terminalregions of the ZmXTH1 protein. Phylogenetic analysis of ZmXTH1reveals that it belongs to subgroup 4, so far only reportedfrom Poaceae monocot species. ZmXTH1 has been expressed in Pichiapastoris (a methylotrophic yeast) and the recombinant enzymeshowed xyloglucan endotransglucosylase but not xyloglucan endohydrolaseactivity, representing the first enzyme belonging to subgroup4 characterized in maize so far. Expression data indicate thatZmXTH1 is expressed in elongating tissues, modulated by cultureconditions, and induced by gibberellins. Transient expressionassays in onion cells reveal that ZmXTH1 is directed to thecell wall, although weakly bound. Finally, Arabidopsis thalianaplants expressing ZmXTH1 show slightly increased xyloglucanendohydrolase activity and alterations in the cell wall structureand composition. Key words: Cell elongation, cell wall, plant transformation, XEH, XET, XTH, Zea mays     

Studies on the Development of the Air Pores and Air Chambers of Marchantia paleacea: 1. Light Microscopy

The ontogeny of the air pores and air chambers of Marchantiapaleacea begins with the schizogenous development of protodermalintercellular spaces of the initial apertures, and is completedwith the formation of the air pores and giant sub-epidermalair chambers bearing numerous photosynthetic filaments. Intercellularspace formation commences from the thallus surface and proceedsinwards to the first internal layer of cells. The cells amongwhich spaces develop do not originate from one mother cell.Spaces are formed only in the regions of the intersection ofthe anticlinal walls of three, four, or sometimes more successivederivatives of S₁, S₃ and S₄ segments of the apical cell, oneor two of which have been divided periclinally and the restanticlinally. Protodermal intercellular spaces appear in mostor all the corners of these cells, the anticlinal walls of whichexhibit an opposite disposition. The S₁, S₂, S₃ and S₄ segmentsare produced by definite divisions of a five-sided apical celland by a series of divisions give rise to initial cells of theinternal layers of the thallus and initial cells of the protodermaland sub-protodermal layers. The concept of a quiescent apicalcell cannot be accepted, since dividing apical cells have beenobserved, and the pattern of wall disposition of the thallusapex cannot be explained without the active participation ofthe apical cell. The air chambers are apparently of exogenous origin. They resultfrom the broadening of the bottom of the initial apertures bythe coordination of the rate of anticlinal divisions and growthof the protodermal and sub-protodermal cells surrounding theintercellular spaces of the initial apertures. The ontogenyof the pore rings starts at an advanced stage of air chamberformation not from a mother cell but from the cells which surroundthe closed entrance of the air chamber, by a shift of the planeof division from anticlinal to periclinal. Before the periclinaldivisions a new axis of growth perpendicular to the thallussurface is established in the mother cells of the pore. By a polarized growth into the air chamber followed by periclinaldivisions, the cells of the floor form initial cells of thephotosynthetic filaments. The latter divide again to form singleor branched photosynthetic filaments. Marchantia paleacea, air pore, air chamber