Function of silica bodies in the epidermal system of rice (Oryza sativa L.): testing the window hypothesis

Silicon has been considered to be important for normal growthand development of the rice plant (Oryza sativa L.). To investigatethe physiological function of deposited silica in rice leaves,the hypothesis that silica bodies in the leaf epidermal systemmight act as a ‘window’ to facilitate the transmissionof light to photosynthetic mesophyll tissue was tested. Thesilica content of leaves increased with supplied silicon andwas closely correlated with the number of silica bodies perunit leaf area in the epidermal system. There was a significantdifference in silica deposition and formation of silica bodiesbetween Si-treated and non-treated leaves; silicon was polymerizedinside the silica cells and bulliform cells of the epidermis,in Si-treated leaves. Although the ‘windows’ wereonly formed in leaves with applied silicon, optical propertiesof leaf transmittance, reflectance and absorptance spectra inSi-treated and non-treated leaves were almost equal. Furthermore,light energy use efficiency and quantum yield of Si-treatedleaves were less than in leaves not containing silica bodies.Thus, silica bodies, at least based on the data, do not functionas windows in rice leaves. Key words: Silicon, window hypothesis, rice, optical property, quantum yield     

CORRECTIONS, VOLUME 29

Part 1, under the frontispiece portrait of Dr. N. B. Eales,the words ‘President 1948–1951’ should havebeen added. Page 103, line 49, for ‘Newton Collection’ read‘Norman Collection (Canon Norman)’. 185, line 37, for ‘capillaris’ read ‘capillacca’. 188, Table 1, for ‘bemoralis’. read ‘nemoralis’. 188, Table 2, for ‘Cochlicella acuta (Müll)? ventrosa(Fér.)’ read ‘Cochlicella ventrosa (Fér.)’. 191, line 24, for ‘araheo-’ read ‘archeo-’.     

Ethylene Production by Fe-deficient Roots and its Involvement in the Regulation of Fe-deficiency Stress Responses by Strategy I Plants

Species that showed marked morphological and physiological responsesby their roots to Fe-deficiency (Strategy I plants) were comparedwith others that do not exhibit these responses (Strategy IIplants). Roots from Fe-deficient cucumber (Cucumis sativusL.‘Ashley’), tomato (Lycopersicon esculentumMill.T3238FER) and pea (Pisum sativumL. ‘Sparkle’) plantsproduced more ethylene than those of Fe-sufficient plants. Thehigher production of ethylene in Fe-deficient cucumber and peaplants occurred before Fe-deficient plants showed chlorosissymptoms and was parallel to the occurrence of Fe-deficiencystress responses. The addition of either the ethylene precursorACC, 1-aminocyclopropane-1-carboxylic acid, or the ethylenereleasing substance, Ethephon, to several Fe-sufficient StrategyI plants [cucumber, tomato, pea, sugar beet (Beta vulgarisL.),Arabidopsis(Arabidopsis thaliana(L.) Heynh ‘Columbia’), plantago(Plantago lanceolataL.)] promoted some of their Fe-deficiencystress responses: enhanced root ferric-reducing capacity andswollen root tips. By contrast, Fe-deficient roots from severalStrategy II plants [maize (Zea maysL. ‘Funo’), wheat(Triticum aestivumL. ‘Yécora’), barley (HordeumvulgareL. ‘Barbarrosa’)] did not produce more ethylenethan the Fe-sufficient ones. Furthermore, ACC had no effecton the reducing capacity of these Strategy II plants and, exceptin barley, did not promote swelling of root tips. In conclusion,results suggest that ethylene is involved in the regulationof Fe-deficiency stress responses by Strategy I plants.Copyright1999 Annals of Botany Company. Arabidopsis (Arabidopsis thaliana(L.) Heynch), barley (Hordeum vulgareL.), cucumber (Cucumis sativusL.), ethylene, iron deficiency, maize (Zea maysL.), pea (Pisum sativumL.), plantago (Plantago lanceolataL.), ferric-reducing capacity, sugar beet (Beta vulgarisL.), tomato (Lycopersicon esculentumMill.), wheat (Triticum aestivumL.).     

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     

Regulation of Storage Protein Synthesis by Sulphur and Nitrogen Nutrition in Cultured Immature Caryopses of Barley

Techniques are described for the culture of developing barley(Hordeum vulgare L.) caryopses. Over a 7 d period in culturethe dry weights and the amounts of starch and protein increasedby at least twofold. Growth was sustained for at least 20 d.The effects of glutamine and cysteine on the amount and compositionof the hordein storage proteins were also studied. Glutaminestimulated total hordein accumulation but caused a disproportionateincrease in the amount of the S-poor ‘C’ hordeinswhen supplied at 100 mol m^–3. Addition of cysteine at1·0 mol m^–3 did not increase the amount of Srich‘B’ hordeins. The results suggest that althoughisolated caryopses are able to take up sucrose and glutamineand convert them to starch and protein there is some limitationin their ability to convert externally supplied cysteine intoproteins. Key words: Hordeum vulgare L., Caryopses, Glutamine, Cysteine, Storage proteins     

X-ray Microanalysis of the Seminal Root of Sorghum bicolor with Particular Reference to Silicon

Sorghum bicolor (L.) Moench. cv. P508.GB plants were grown inwater culture for 1 week, when the seminal roots were harvestedand sampled at five positions starting from the base: 0.0, 0.25,0.50 and 0.75 of the axis length, and a sub-apical position,11 mm behind the tip. Mineral distribution in bulk frozen rootsegments was investigated using SEM and X-ray microanalysis.The elements detected were potassium, chlorine, sulphur, sodium,phosphorus, calcium and silicon. The first four occurred inall root zones. Phosphorus was ubiquitous, but appeared to accumulatein the pericycle protoplasm. Calcium and silicon exhibited themost variation along the seminal axis. Calcium was present inall tissues at the base, but decreased acropetally, being detectedin only the outer cortical and epidermal walls of the subapicalzone. Silicon was present at low levels in protoplasts and wallsof most root tissues, and accumulated in the endodermal protoplastand walls. Deposition in walls is initiated coincident withthe earliest stages of secondary wall thickening. Silicon contentof the inner tangential wall of the endodermis exhibits a decreasingacropetal gradient along the axis length. It is absent frommost cell walls of the sub-apical zone. Silicon pathways inthe root, and silica aggregate formation in relation to thesurrounding ionic environment, are discussed. Sorghum bicolor (L). Moench, seminal root, cryostage, SEM, X-ray microanalysis, ion localization, silicon, endodermis     

Anther Culture of Lolium temulentum, Festuca pratensis and Lolium x Festuca Hybrids. I. Influence of Pretreatment, Culture Medium and Culture Incubation Conditions on Callus Production and Differentiation

This study was conducted with Lolium temulentum, Festuca pratensis,and the two hybrids L. multiflorum x F. pratensis ‘Elmet’and L. perenne x F. pratensis ‘Prior’. In a comparisonof various durations (7–42 d) of pretreatment at 4 or7 °C the highest yield of microspore-derived callus of L.temulentum was obtained after pretreatment of spikes at 7 °Cfor 28 d, conditions which also proved optimal for panicle pretreatmentwith F. pratensis. For ‘Elmet’, durations of 21–42d were optimal, and for ‘Prior’ the responses tendedto decline with increasing duration. In L. temulentum addition of charcoal (1–2 g l^–1)to medium containing 2, 4-D and KN wa     

Transient Expression of Exogenous DNA in Intact, Viable Wheat Embryos Following Particle Bombardment

Expression of foreign DNA has been detected in intact, germinatingwheat embryos (Triticum aestivum L.) following bombardment withtungsten particles complexed with a reporter gene encoding thebacterial enzyme ß-glucuronidase (‘GUS’:E.C.3.2.1.31). Expression was detected in situ in individualcells and groups of cells, by supplying the germinating embryoswith the chromogenic substrate of the GUS enzyme, ‘X-gluc’.Expression was dependent on the presence of a constitutive plantpromoter, the Cauliflower Mosaic Virus ‘35S’ promoter,fused to the GUS structural coding sequence. The relative simplicityof this technique recommends its future use for the assay ofregulatory elements which control the spatial and temporal specificityof genes expressed during embryo development. Key words: Transient expression, particle bombardment, wheat embryo, Triticum aestivum L.     

Leaf and Tiller Production of Prairie Grass (Bromus willdenowii Kunth) and Two Ryegrass (Lolium) Species

A detailed morphological study of three prairie grass cultivars(Bromus willdenowii Kunth) was conducted under ‘vegetative’and ‘reproductive’ growth conditions (short andlong photoperiods) and at different temperatures. Perennialryegrass (Lolium perenne L.) and Westerwolds ryegrass (Loliummuhiflorum Lam.) were compared during vegetative growth. Prairie grass had higher leaf appearance rates (leaves per tillerper day) and lower site filling (tillers per tiller per leafappearance interval) than the ryegrass species. Tillering rates(tillers per tiller per day) were also lower, except under vegetativeconditions at 4C. Low tiller number in prairie grass was notdue to lack of tiller sites but a result of poor filling ofthese sites. Lower site filling occurred because of increaseddelays in appearance of the youngest axillary tiller and lackof axillary tillers emerging from basal tiller buds. In prairiegrass, no tillers came from coleoptile buds while only occasionallydid prophyll buds develop tillers. Low tiller number in prairiegrass was compensated for by greater tiller weight. Prairiegrass had more live leaves per tiller, greater area per leafand a high leaf area per plant. Considerable variation between cultivars was found in prairiegrass. The cultivar ‘Bellegarde’ had high leaf appearance,large leaves and rapid reproductive development, but had lowlevels of site filling, tillering rate, final tiller numberand herbage quality during reproductive growth. ‘Primabel’tended to have the opposite levels for these parameters, while‘Grasslands Matua’ was intermediate and possiblyprovided the best balance of all plant parameters. prairie grass, Bromus willdenowii Kunth, perennial ryegrass, Lolium perenne L., Westerwolds ryegrass, Lolium multiflorum Lam., temperature, photoperiod, leaf appearance, leaf area, tillering, site filling, tillering sites, yield     

Endodermal Silicon Deposits and Their Linear Distribution in Developing Roots of Sorghum bicolor (L.) Moench.

Seedlings of Sorghum bicolor (L.) Moench. were cultured in nutrientsolution containing 100 p.p.m. SiO₂. Over periods up to 14 days,the progressive accumulation of Si deposits was recorded bymeans of the electron-probe microanalyser and the scanning electronmicroscope along the seminal root length. An acropetal, linear gradient of Si deposits developed in theendodermis, beginning at the proximal end of the root after1 day, and subsequently extended distally until after 7 days,the total silicified endodermal zone occupied the proximal 75per cent of the root length, a value which remained relativelyconstant thereafter, in spite of root extension. No Si was detectedbelow this zone towards the apex. This result is believed tobe related directly to the asynchronous gradient of cell maturationexhibited by the endodermis behind the apex, and specificallyto the degree of wall development therein. Opaline silica was deposited only in the endodermis, initiallyon the inner tangential wall (ITW) surface after only 1 day,as spherical masses of coalesced, primary particles for whichthe term ‘silica aggregate’ is proposed. A thinlayer of silica over the wall surface was formed as a secondaryphase. The aggregates reached mature size after approximately7 days. Conditions favourable to the inception of silica depositionare discussed including the significance of the chemical compositionof the aggregates, and the importance of the degree of cellulosicthickening, as well as the surface characteristics, of the ITW.     

Nature of 'Pollinator' Effect in Potato (Solanum tuberosum L.) Haploid Production

Haploids (2n =24) of the common tetraploid (2n=48) potato (SolanumtuberosumL.) provide promising material for attacking many problemsconcerned with the genetics, cytogenetics and breeding of thisspecies. Interspecific 4xx2xcrosses betweenSolanum tuberosumgp.Andigenaorgp.Tuberosumcultivars as pistillate parents andSolanum tuberosumgp.Phurejaassource of pollen (hereafter ‘pollinator’) have beenused to produce maternally derived haploids through parthenogenesis.This paper discusses the nature of the ‘pollinator’effect in haploid extraction. The ‘pollinator’ hada significant effect on haploid frequencies following 4xx2xcrosses.The ‘pollinator’ effect seems to operate via theendosperm, in which haploid (n=2x) embryos are associated withhexaploid endosperm. A superior ‘pollinator’ appearsto have its effect by contributing two haploid (n) gametes tothe central cell. 2n pollen; double fertilization; endosperm; ploidy manipulations; Solanum tuberosum     

Studies in the Bangioideae III. The Life-history of Porphyra umbilicalis (L.) Kutz. var. lociniata (Lightf.) J. Ag.: A. The Conchocelis-Phase in culture

As the first step in an investigation of the life-history ofPorphyra umbilicalis (L.) Kütz. var. laciniata (Lightf.)J. Ag., spores which have originated as a result of the repeateddivision of the mother-cells have been germinated. When grownon glass their method of germination and growth agrees withthat described by previous investigators, but when germinatedon sterile shell the germ-tubes penetrate the shell and developinto growths identical with Conchocelis rosea Batters. This‘species’, therefore, is a phase in the life-historyof P. umbilicalis var. laciniata and not an autonomous species.The development of the ‘Conchocelis’-phase in cultureis described and also the formation of fertile cell-rows and‘plantlets’. Until the significance of these structuresis understood and a cytological investigation completed, therelationship of the intertidal leafy Porphyra-thallua to thefilamentous, shell-inhabiting, deep-water Conchocelis cannotbe expressed in the terms usually employed to denote the variousphases of the life-histories of algae.     

Anther Culture of Lolium temulentum, Festuca pratensis and Lolium x Festuca Hybrids. II. Anther and Pollen Development In Vivo and In Vitro

The various pathways of pollen development were investigatedin cultured anthers of Lolium temulentum, Festuca pratensisand the L. multiflorum x F. pratensis hybrid ‘Elmet’.In all three, development from the vegetative cell was the predominantpathway of pollen callus development. However, there were characteristicdifferences in the behaviour of the generative cell. In L. temulentumit remained attached to the pollen wall and degenerated, whereasin F. pratensis it divided. In ‘Elmet’ it detachedfrom the pollen wall and remained undivided. Both polarizedand unpolarized partitioned calluses were observed. Developmentof the fusion product of the vegetative and generative nucleiwere also observed in anthers of L. temulentum. Anomalous grainswere not found to be major source of pollen calluses. Sections of anthers of L. temulentum were used to investigatethe origin of S pollen grains, the small pale-staining grainswhich denote pollen dimorphism. Such grains form out of contactwith the tapetum and are therefore determined before or duringmeiosis (i.e. before harvest of anthers for culture). Sectionswere also used to demonstrate the influence of the durationof pretreatment on the development of the middle layer of theanther wall. Festuca pratensis, Lolium temulentum, Lolium x Festuca, anther culture, haploid, microspore, pollen     

The Galls on Forsythia intermedia Zab.

The galls on Forsythia intermedia Zab. consist of much-branched,root-like structures embedded in corky material which appearsto be sloughed-off from them. These gall ‘roots’have 7 to 14 vascular bundles compared with the 5 of normalroots and contain much more IAA. When galls were incubated in damp chambers the gall ‘roots’extended their growth. These extensions had a root-cap and root-hairsbut also had more vascular bundles than normal and they didnot respond geotropically like normal roots. Two fungi, Gibberella baccata (Wallr.) Sacc. (conid, stat. Fusarlumlateritium Nees.) and Phomopsis dominici Trav. were associatedwith die-back of gall ‘roots’ and two bacteria resemblingCorynebacterium fascians (Til.) Dowson and Agrobacterium tumefaciens(Sm. and Towns.) Conn respectively were isolated from galls.All produced IAA in culture media but their role in the etiologyof the gall, if any, remains in doubt.     

The Ultrastructure and Analytical Microscopy of Silicon Deposition in the Aleurone Layer of the Caryopsis of Setaria italica (L.) Beauv.

Silicon deposition in the caryopsis of foxtail millet (Setariaitalica (L.) Beauv.) from Lin Xian, Northern China was investigatedusing transmission electron microscopy and energy dispersiveX-ray analysis. The highest silicon count rates were obtained from the pericarpand outer aleurone cell walls, and particularly from a granularelectron-opaque layer external to the outer aleurone cell wall.Silicon was not detected in tissues interior to the aleurone. A possible mechanism for silicon deposition in the caryopsisis suggested, and the results are discussed with respect tothe high incidence of oesophageal cancer in Lin Xian, NorthernChina. Setaria italica (L.) Beauv., foxtail millet, silicon deposition, alcurone layer, caryopsis, ultrastructure, X-ray analysis     

Dimorphism and Monomorphism in the Plumbaginaceae: II. Pollen and Stigmata In the Genus Limonium

A survey of pollen- and stigma-dimorphism and monomorphism inthe genus Limonium (as understood at present) reveals considerableheterogeneity which is useful for the solution of taxonomic,phylogenetic, and phytogeographic problems. Two main pollen types (A and B) and two main stigma types (coband papillate) occur in the genus. Capitate stigmata also occur. ‘Type A’ pollen has frequently been found in conjunctionwith ‘papillate’ stigmata as a secondarily monomorphic(self-compatible) combination and this must have arisen at leastfour times in the genus as well as in Armeria. ‘Type B’pollen and ‘cob’ stigmata are recorded togetherfor the first time (also as a secondarily monomorphic, self-compatiblecombination) in L. echioides. Apomixis, already discovered insubsections Densiflorae and Dissitiflorae, has been found inL. cosyrense of the subsection Steirocladae. The taxonomic and phylogenetic significance of the facts indiscussed.     

The Nitrogen Content of Plants and the Self-thinning Rule of Plant Ecology: A Test of the Core-skin Hypothesis

The ‘core-skin’ hypothesis postulates that secondarilythickened plants behave energetically as an inert ‘core’covered by an active ‘skin’, the ‘skin’being two-imensional, the ‘core’ three-dimensional.This would explain the ‘self-thinning ‘or‘–3/2’ rule of plant ecology, that is, the tendencyfor log (dry weight per plant) and log (number of plants perunit area) to progress along a straight line relationship, withslope = – 3/2’. The hypothesis was tested as follows. Plant nitrogen contentwas used as an estimate of the mass of ‘skin’ perplant, and dry weight as an estimate of the mass of the ‘core’.As plants mature the slope of the relationship between y = log(mass of nitrogen per plant) and x = log (mass of dry matterper plant) is expected to decline from an initial value of 1.0towards a final value of 0.66. The intercept of the relationshipis expected to reflect the intrinsic content of ‘skin’per unit of ‘core’. Genotypic variation in thisparameter should cause genotypic differences in the maximumattainable yield of biomass per unit area. The expectations were investigated by fitting the function y= p+qx+r exp – x to 30 sets of data on plant nitrogencontent, plant weight and time in 18 different vegetables. Simplelinear regressions of y on x were fitted to more limited setsof data on weights and nitrogen contents of mature trees. Theexpectations were, with some minor exceptions, confirmed. Nitrogen, yield, plant competition, self-thinning     

Leaf Characteristics and Net Gas Exchange of Diploid and Autotetraploid Citrus

The effect of tetraploidy on leaf characteristics and net gasexchange was studied in diploid (2x ) and autotetraploid (4x) ‘Valencia’ sweet orange (Citrus sinensis (L.)Osb.) and ‘Femminello’ lemon (Citrus limon (L.)Burm. f.) leaves. Comparisons between ploidy levels were madeunder high irradiance (I) in a growth chamber or low total Iin a glasshouse. Tetraploids of both species had thicker leaves,larger mesophyll cell volume and lower light transmittance thandiploids regardless of growth I. Mesophyll surface area perunit leaf area of 2x leaves was 5–15% greater than on4x leaves. Leaf thickness and mesophyll cell volume were greaterin high I leaves than low I leaves. In high I, average leafarea was similar for 2x and 4x leaves, whereas in low I it was30% greater in 4x than in 2x leaves. Nitrogen and chlorophyllconcentration per cell increased with ploidy level in both growthconditions. The ratio of chlorophyll a:b was 25% greater in2x than in 4x leaves. When net CO₂assimilation rate (A_CO2) wasbased on leaf area, 4x orange leaves had 24–35% lowerA_CO2than their diploids. There were no significant differencesin A_CO2between 2x and 4x orange or lemon leaves when expressedon a per cell basis. Overall, lower A_CO2per unit leaf area oftetraploids was related to increase in leaf thickness, largermesophyll cell volume, the decrease in mesophyll area exposedto internal air spaces, and the lower ratio between cell surfaceto cell volume. Such changes probably increased the resistanceto CO₂diffusion to the site of carboyxlation in the chloroplasts. Cell volume; chlorophyll; irradiance; leaf thickness; nitrogen; photosynthesis; ploidy; Citrus limon ; C. sinensis ; ‘Valencia’ sweet orange; ‘Femminello’ lemon     

Abnormal Stomatal Opening in Coconut Palms Affected with Root (Wilt) Disease

Studies on the stomatal regulation in the root (wilt) affectedcoconut palms (Cocos nucifera L.) revealed that the diseasedpalms had low stomatal resistance compared to the healthy palms,irrespective of their age. The same trend was observed whetherthe determinations were made at different times of the day (6–18h) or under irrigated and unirrigated conditions or in differentseasons (‘dry’ and ‘wet’). Thus, thestomatal regulation was significantly impaired in the diseasedpalms resulting in excessive water loss compared to the healthypalms. Results are discussed with the available literature onother similar disease caused by fungi, bacteria and mycoplasma-likeorganisms in different plants. Key words: Cocos nucifera L., Stomatal resistance, Root (wilt) disease     

Morphology and Anatomy of Stems and Pedicels of Spring Flush Shoots Associated with Citrus Fruit Set

Flowering and vegetative shoots of ‘Shamouti’ orange[Citrus sinensis (L.) Osbeck] and ‘Marsh’ seedlessgrapefruit (Citrus paradisi Macf.) were examined for correlationof their morphology and anatomy with fruit set. Fruit set isfavoured on leafy inflorescences whereas abortion is nearlycomplete on leafless inflorescences. Leafless inflorescencesof ‘Shamouti’ with one flower were found to havea very thin stem which contained few vascular bundles, whereasthose with three flowers had better-developed vascular systems.The vascular system of leafy inflorescences is significantlydifferent from that of leafless ones and contains a distinctcentral xylem cylinder. The vascular area of leafless inflorescencesis only about one-quarter of that of the leafy ones. The vascularsystem of grapefruit resembles that of the ‘Shamouti’orange. This study emphasizes the importance of the dimensionof the vascular system for fruit set and provides a possibleexplanation for the better fruit set on both leafy and leaflessinflorescences with several flowers compared with single-floweredinflorescences. Anatomy; citrus; fruit set; leafless inflorescence; leafy inflorescence; pedicel; vascular system; vegetative shoot