Intracellular Silica Deposition in Immature Leaves in Three Species of the Gramineae

The formation of solid, discrete deposits of opaline silicawithin the cell lumen of leaf tissues is reported in speciesrepresenting three subfamilies of the Gramineae; the preparationof a silica-minimal nutrient solution is discussed. Opal phytolithnumbers are related to tissue age and to two external silicaconcentrations for tiller leaves over a period of 32 days followingbud initiation. Variations in silica deposition patterns among the individualleaves of a homologous series on the shoot apex are relatedto differential growth-rates. During ontogeny, deposition occursin an ordered sequence of cell types related to the basipetalmaturation gradient within the leaf. Initial deposition wasdetected in silica cells (idioblasts) of imbricated, bud leavesof Sieglingia decumbens, 1 mm long; phytoliths are confinedto these cells in expanding, basal portions of the leaf. Phytolithcounts/sq mm of epidermis vary with the degree of long-cellexpansion. The error is reduced by expressing silicificationas the number of phytoliths/100 silica cells. Post-expansiondeposition was initiated in epidermal long cells of the leafblade tip. The higher silica concentration resulted in a morerapid utilization of available deposition sites and larger phytoliths(P = 0.001). A passive cell influx of silicic acid is discussedin relation to cytodifferentiation.     

Silica Spicules in Canary Grass

The hairs occurring on the surface and the persistent bractsof the fruits of canary grass (Phalaris canariensis) consistof opaline silica spicules emerging from the abaxial epidermalcells. They are approx. 500 µm long and taper from a diameterof 15 um at the base to a tip radius of 0.3 µm. Thesespicules are found in the diet of people living in areas inwhich very high incidences of oesophageal cancer occur. Themicrostructure of cleaned spicules is complex and differes fromthat of mineral opal and also from tabashir, a plant opal occurringin bamboo, which is a relatively unstructured emulsion of silicaparticles. Phalaris canariensis, silica deposits, silicification, hairs, electron microscopy, lectron-probe, microanalysis     

Opaline Silica Deposition in Rye (Secale cereale L.)

The types of opaline silica-bodies (opal phytoliths) which occurin the mature prophylls, radical and culm leaves, culms, andinflorescence bracts of rye (Secale cereale L.) are describedand figured. Silica-bodies are absent from the coleoptile, andthe adaxial epidermis of the prophylls, leaf sheaths, and inflorescencebracts. The stages of silica-body formation in young radicalleaf sheaths are also described. Alternative hypotheses forthe origin of silica-bodies are discussed.     

Opaline Silica Deposits in the Leaves of Bidens pilosa L. and their Possible Significance in Cancer

The occurrence of silica deposits in suitably treated leavesof Bidens pilosa L. of African origin was investigated usinglight and scanning electron microscopy and X-ray analyses. Numerousfibres of amorphous silica were located at the edges and surfacesof the leaves. The deposits were always associated with theepidermal microhairs and were confined to the walls. The significance of these accumulations in a dicotyledonousspecies and in relation to possible deposition mechanisms isdiscussed. Their possible role as a cause of cancer is reviewedin the light of recent investigations involving Bidens pilosa. Bidens pilosa L., opaline silica, oesophageal cancer     

Silica Deposition in Some C3 and C4 Species of Grasses, Sedges and Composites in the USA

We report new information on silica deposition in 15 plant species,including nine grasses, two sedges and four composites. Thesilica depositional patterns found in seven of the grass speciesindicate that they are C₄ plants. However the festucoid grassCortaderia selloana is a C₃ plant with long leaf trichomes andoval silica structures in the leaves. In contrast the panicoidC₄ grasses Chasmathium latifolium, Chasmathium sessiflorum,Imperata cylindrica, Panicum repens, Panicum commutatum andSetaria magna, all produce dumb-bell-shaped silica structuresin the leaves. The chloridoid grasses Spartina patens and Spartinacynosuroides have saddle-shaped structures and no dumb-bellor oval shaped ones. The sedges Rhynchospora plumosa and Scirpuscyperinus were found to have oval phytoliths and may be C₃ plants.Our examination of these and other grasses strongly suggeststhat C₄ grasses tend to produce the same type of silica cells.Grasses and sedges with C₃ type photosynthesis tend to produceoval silica structures. The composite Grindelia squarrosa andsunflowers Helianthus angustifolia, Helianthus atrorubens andHelianthus tuberosus absorb relatively small amounts of siliconand larger amounts of calcium, where both elements deposit inleaf trichomes. We found no clear indicator for the C₃ sunflowersor C₄ types in the Asteraceae. Helianthus tuberosus leaves havemany trichomes on the adaxial surface. These trichomes havea higher concentration of silica than the surrounding leaf surface.Helianthus tuberosus leaves had much higher ash and silica contentsthan those of Helianthus angustifolia and Helianthus atrorubens.The composite Grindelia squarrosa has a usual deposition ofsilica in the basal cells around the guard cells. Silica depositionoften reflects the surface features of a leaf. An exceptionis Scripus cyperinus where the silica structures are deep inthe tissue and do not reflect the surface configurations. Theinforescence of Setaria magna had a 14.64 silica content. Thetufts of white, silky hairs characteristic of Imperata cylindricainflorescence have no silica. C₃ and C₄ plants, silica and ash content, scanning electron microscopy, energy-dispersive X-ray analysis, silicon distribution, spectra of elements in plants, trichomes, silica fibres, phytoliths     

ECOTYPIC DIFFERENTIATION WITHIN FOUR NORTH AMERICAN PRAIRIE GRASSES. I. MORPHOLOGICAL VARIATION WITHIN TRANSPLANTED COMMUNITY FRACTIONS

Ecological variation within transplanted community fractions, containing Andropogon scoparius Michx., A. gerardi Vitman, Panicum virgatum L. and Sorghastrum nutans (L.) Nash, included broad behavioral and morphological differentiation. In Austin, Texas, during 1958–1962, southern community fractions that contained early spring activity, late flowering and late fall dormancy included taller plants than early-flowering, northern community fractions. The tallest populations in all 4 species originated in Texas. In P. virgatum, size of leaves and panicles showed north-south trends similar to culm height values. Leaf pubescence and leaf glaucousness in all 4 species showed geographic patterning that was not correlated with north-south maturity gradients. Greatest pubescence was on clones in community fractions from pine woods in the Southeast. Glaucousness was concentrated in community fractions from central Texas northward to Nebraska.     

The ratio of germanium to silicon in plant phytoliths: quantification of biological discrimination under controlled experimental conditions

Slight differences in the chemical behavior of germanium (Ge) and silicon (Si) during soil weathering enable Ge/Si ratios to be used as a tracer of Si pathways. Mineral weathering and biogenic silicon cycling are the primary modifiers of Ge/Si ratios, but knowledge of the biogenic cycling component is based on relatively few studies. We conducted two sets of greenhouse experiments in order to better quantify the range and variability in Ge discrimination by plants. Graminoid species commonly found in North American grassland systems, Agropyron smithii, Schizachyrium scoparium, and Andropogon gerardii were grown under controlled hydroponic environmental conditions. Silicon leaf contents were positively correlated with solution Si and ambient temperature but not with nutrient solution pH, electrical conductivity, or species. The Ge/Si ratio incorporated into phytoliths shows a distribution coefficient [(Ge/Si)_phytolith/(Ge/Si)_solution] of about 0.2 and is remarkably invariant between species, photosynthetic pathway, and solution temperature. Ge seems to be discriminated against during the uptake and translocation of Si to the opal deposition sites by about a factor of five. In the second experiment, a wider range of graminoid species (Agropyron smithii, Bouteloua gracilis, Buchloe dactyloides, Oryzopsis hymenoides, Schizachyrium scoparium and Andropogon gerardii) were grown in two different soil mediums. Plant phytoliths showed a distribution factor of about 0.4 for field grown grasses, and 0.6 for potting soil grown grasses with no clear trends among the species. Evidence of the direction and degree of biological Ge discrimination during plant uptake provides a geochemical finger print for plants and improves the utility of Ge/Si ratios in studies of terrestrial weathering and links between Si cycles in terrestrial and marine systems.     

NATURE OF THE PLANT COMMUNITY. VI. TEXAS GRASSLAND COMMUNITIES UNDER TRANSPLANTED CONDITIONS

Mc Millan , Calvin . (U. Texas, Austin.) Nature of the plant community. VI. Texas grassland communities under transplanted conditions. Amer. Jour. Bot. 48(9): 778–785. Illus. 1961.—Clones of 7 grass taxa, Bouteloua gracilis (H. B. K.) Lag., B. eriopoda (Torr.) Torr., B. curtipendula (Michx.) Torr., Panicum virgatum L., the Andropogon scoparius Michx. complex, the Andropogon gerardi Vitman-hallii Hack. complex, and Sorghastrum nutans (L.) Nash, were transplanted from throughout their distribution in Texas and studied in an experimental garden at Austin. Restricted to western Texas and Panhandle areas, Bouteloua gracilis and B. eriopoda contained similar early-flowering clones throughout their distribution. Less restricted to western sites, B. curtipendula contained later-flowering types from eastern and central areas. In the 4 remaining, widespread taxa, early-flowering potential characterized clones from western sites. These 4 widespread taxa contain the latest-flowering clones from the coast of southern Texas. Clones of Stipa leucotricha Trin. and Rupr. from a broad area in Texas lacked a flowering gradient. Grassland communities of western Texas and the Panhandle, attuned to short growing seasons and low rainfall, were composed of opportunists, the Bouteloua species, and early-flowering variants within the widespread species. Communities of central Texas in habitats of highly unpredictable moisture pattern and a relatively long growing season contained later-flowering variants. Coastal communities attuned to a long growing season contained the latest-flowering variants.     

Opaline gland ultrastructure in Aplysia californica (Gastropoda: Anaspidea)

Secretions released from the ink and opaline glands of Aplysiacalifornica protect this shell-less mollusc from predators inseveral ways; the most recently discovered, phagomimicry, stimulatesthe feeding behaviours of the predator, distracting it fromthe sea hare. The structure of the ink gland has been reported,but little is known about the opaline gland. This paper comparesthe structure of the opaline gland of A. californica with thatof its ink gland, as well as two additional vesicle types foundin the epidermis. The opaline gland consists of single largecells, the vesicle cells, each with an enlarged nucleus, themaximum size of both exceeding that of respective structuresin the ink gland. Opaline vesicles, like ink vesicles, are enclosedby an external layer of muscle. Opaline vesicles, unlike inkvesicles, are not immersed in additional cells, but are freewithin the haemolymph and are, therefore, the probable sitefor the synthesis of their protein contents. The necks of individualopaline vesicles are fused into a central canal, but short necksconnecting each vesicle to the central canal remain; these arefilled with epithelial cells, but lack a muscular release valvelike that in the long necks of ink vesicles. Mucous cells containcircular arrays and are structurally distinct from opaline vesicles;mucous cells, though enlarged, are smaller than opaline or inkvesicle cells; they lack an external layer of muscle and a multicellularneck and, therefore, more closely match another vesicle typein the skin of A. californica, the white vesicle, which is involvedwith excess calcium excretion. (Received 22 September 2006; accepted 20 March 2007)     

Intracellular Silica Deposition in Mature and Senescent Leaves of Sieglingia decumbens (L.) Bernh

Following 1, 2, 4, or 8 weeks of growth in a silica-minimalsolution, tillers of Sieglingia decumbens (Heath Grass) weretransferred for 8 days to a nutrient solution which contained50 or 100 ppm silica. The resultant formation of intracellularopal phytoliths (silica bodies) was compared for the four developmentalstages of leaf 3. Characteristically different phytolith typesoccurred in leaves of different ages. Senescent, in contrastto younger, mature leaves, typically exhibited extensive extracellularsilicification of the mesophyll, in addition to deposits instomatal, long, and bulliform cells of adaxial epidermis; depositionin abaxial silica cells and long cells, characteristic of youngleaves, was much reduced, or absent. Physico-chemical factors and cytoplasmic changes associatedwith senescence are discussed in relation to intracellular opalphytolith formation in mature leaves of S. decumbens. In thisrespect, the tendency of silicic acid sols to polymerize inthe presence of an organic matrix and mineral cations is consideredto be significant.     

Silica and Ash in Native Plants of the Central and Southeastern Regions of the United States

Ash and silica contents and depositional patterns were determinedfor different tissues of 11 plants growing in the southeasternand central parts of the USA. Silica content was high in theleaves, sheaths and inflorescences of the grasses studied, especiallyso in the inflorescence of the C₃ grass, Stipa comata Trise.and Rupr. The ash content was especially high in leaves of Polymniauvedalia L., which are also high in calcium. Calcium depositionwas largely in trichomes and in veins of the leaf. Energy-dispersiveX-ray analysis showed that the distribution of the element siliconis closely related to certain epidermal structures such as ridges,cell walls, rows of irregularly-shaped structures lying lenghthwisealong the leaf, dumb-bell shaped structures and trichomes. Thesestructures also correspond to the phytoliths left behind afterdecay of the plant. The C₃ grasses differed from the C₄ in thatthey showed oval structures and produced correspondingly ovalphytoliths. Silicified trichomes (particularly in the C₃ grasses)and long, narrow, silica fibres were common in the inflorescencesof the grasses studied. These sharp particles could be irritatingto oesophageal and other tissues. Similar fibres in other grasseshave been implicated in certain cancers. High silicificationof the inflorescence structures might afford protection forthe seed, as reported for other grasses. C₃ and C₄ grasses, silica and ash content, scanning electron microscopy, energy-dispersive X-ray analysis, silicon distribution, spectra of elements in plants, trichomes, silica fibres, phytoliths     

Electron-probe Microanalysis Studies of Silica Distribution in Barley (Hordeum sativum L.)

Silicon occurence has been investigated by means of epidermalpeels, cryostat, and ultrathin sections of the internode, nodes,leaves, inflorescence bracts, and caryopsis of Hordeum sativumL. (cultivar Deba Abed) using the electron probe microanalyser.Analyses were made on growth stages during ear emergence andat maturity. The results indicate that silicon is present inthe internode with the highest concentration associated withthe opaline deposits. Detectable quantities are also found inthe outer tangential walls of the long cells, in the walls ofstomata, the sclerenchyma, and all vascular bundle regions.In mature upper internodes, silicifiation is confined to theupper third region, but this limit extends closer to the basalmeristem with increasing age of internode. The nodes have agreater concentration in the radial than in outer tangentialwalls. Heavy deposits are found in the leaves but with considerablevariation between blade and sheath, abaxial and adaxial surfaces,and the leaf position. The flag leaf contained the highest accumulations. In the inflorescence bracts (lemma and palea), silicon is detectableonly in the abaxial epidermis and hypodermis. Awns are alsoheavily silicified with the highest concentrations in the sclerenchymaand trichomes.     

The role of water level and salinity in the regulation of Juncus gerardi populations in former ricefields in southern France

Abstract. In the Rhône delta (southern France) Juncus gerardi is a dominant, strongly aggregating species in artificially flooded former rice fields. In order to explain this pattern, the effects of water depth, salinity and their interaction were measured on (1) seed germination and seedling development and (2) vegetative growth of J. gerardi in a controlled-environment experiment. The germination pattern of J. gerardi was affected by salinity. Low salinity (2 g/l NaCl) delayed germination while moderate salinity (12 g/l NaCl) reduced germination rate. In contrast, the germination of J. gerardi was not affected in the range of water depths tested (i.e. 0–10cm). Salinity negatively affected the development of below-ground parts, shoots and inflorescences. This negative effect of salinity on the vegetative growth of J. gerardi was amplified when combined with flooding. Flooding with fresh water (0–20 cm depth) did not limit biomass production during the experiment. However, a decrease in the ratio of below-ground/above-ground dry weight at deeper water depths suggests a limitation of the vegetative propagation of J. gerardi under prolonged flooding conditions. This hypothesis is supported by the negative correlation between the cover of J. gerardi and water depth found in an abandoned rice field. The limitation on seedling recruitment imposed by salinity and the depression of vegetative growth of J. gerardi due to a combination of salinity and water depth could explain the aggregate distribution of J. gerardi in former rice fields.     

A Test for the Resource Remobilization Hypothesis: Tree Sprouting using Carbohydrates from Above-ground Parts

To test the resource remobilization hypothesis, i.e. the hypothesisthat some trees sprout from root-collars or from the lower partof trunks using resources obtained from above-ground parts ratherthan from resources reserved in their roots, we conducted cuttingexperiments forEuptelea polyandra, a frequently sprouting treespecies with little carbohydrate reserves in its roots,Quercusserrata,a frequently sprouting tree species with large reservesin the roots, andMallotus japonicus, a rarely sprouting treespecies. Trees of each species were cut down in winter leavingtwo kinds of stumps, those approx. 1.5 m in height and thosecut off near the ground. The number and total dry weight ofnewly sprouted shoots per stump were compared between the twotreatments and among the three species at the end of the followinggrowing season. InE. polyandra,both the number and total dryweight of sprouts per stump were very small for both treatmentsand were similar to, or less than, those ofM. japonicus. Onthe other hand,Q. serratasprouted abundantly in both treatments.These results indicate thatE. polyandracannot sprout sufficientlywithout a considerably large volume of above-ground parts orthat additional structures such as foliage and branches maybe necessary for sprouting. We conclude that the resource remobilizationhypothesis is supported for this species.Copyright 1998 Annalsof Botany Company Euptelea polyandraSieb. et Zacc,Quercus serrataThunb,Mallotus japonicus(Thunb.) Muell. Arg., tree sprouting, cutting experiment, resprouter, resource movement, carbohydrate allocation, ground-surface disturbance, root stock, resource remobilization hypothesis.     

ECOTYPIC DIFFERENTIATION WITHIN FOUR NORTH AMERICAN PRAIRIE GRASSES. II. BEHAVIORAL VARIATION WITHIN TRANSPLANTED COMMUNITY FRACTIONS

Ecotypic differentiation in transplanted clones of Andropogon scoparius Michx., A. gerardi Vitman, Panicum virgatum L. and Sorghastrum nutans (L.) Nash showed north-south correlations. In Austin, Texas, during 1959–1962, southern populations had earliest spring activity, latest flowering and latest dormancy. Northern community fractions from Massachusetts to North Dakota showed early flowering and a short span separating initial anthesis among the species-populations. Community fractions from Virginia to Nebraska had initial anthesis over a longer period than in more northern or more southern samples. Community fractions from South Carolina to eastern Texas had late flowering over a short period. Western community fractions, latitudinally and altitudinally diverse, were behaviorally uniform. The length of the growing period and its recurrent selection have sorted out ecological variants in harmony with the habitat gradients. Whether they are of the predominant physiognomic types, as in the true prairie region, or understory plants in the pine forests, the 4 grass taxa are in the climax matrix.     

Accumulation of germanium (Ge) in plant tissues of grasses is not solely driven by its incorporation in phytoliths

Ge/Si ratios of plant phytoliths have been widely used to trace biogeochemical cycling of Si. However, until recently, information on how much of the Ge and Si transferred from soil to plants is actually stored in phytoliths was lacking. The aim of the present study is to (i) compare the uptake of Si and Ge in three grass species, (ii) localize Ge and Si stored in above-ground plant parts and (iii) evaluate the amounts of Ge and Si sequestrated in phytoliths and plant tissues. Mays (Zea mays), oat (Avena sativa) and reed canary grass (Phalaris arundinacea) were cultivated in the greenhouse on soil and sand to control element supply. Leaf phytoliths were extracted by dry ashing. Total elemental composition of leaves, phytoliths, stems and roots were measured by ICP-MS. For the localization of phytoliths and the determination of Ge and Si within leaf tissues and phytoliths scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) was used. The amounts of Si and Ge taken up by the species corresponded with biomass formation and decreased in the order Z. mays > P. arundinacea, A. sativa. Results from LA-ICP-MS revealed that Si was mostly localized in phytoliths, while Ge was disorderly distributed within the leaf tissue. In fact, from the total amounts of Ge accumulated in leaves only 10% was present in phytoliths highlighting the role of organic matter on biogeochemical cycling of Ge and the necessity for using bulk Ge/Si instead of Ge/Si in phytoliths to trace biogeochemical cycling of Si.

     

Electron-probe Microanalysis Studies of Silicon in the Elongating Basal Internodes of Avena sativa (L.), Hordeum sativum (Jess.) and Triticum aestivum (L.)

Silicon deposits in the elongating basal internodes of almostmature, field grown specimens of Avena sativa, Hordeum sativumand Triticum aestivum were investigated using electron-probemicroanalysis. In A. sativa and H. sativum silicon was foundto be confined to the cells in the endodermal layer, being presentwithin the inner tangential and radial walls, and occasionallyin the outer tangential wall. In T. aestivum some silicon wasalso located in walls of cells surrounding the vascular bundles. The anatomy of the internodal tissues is discussed for the threespecies from light micrographs. The endodermal layer is discontinuousin A. sativa and H. sativum, in the former species it partlyextends around individual vascular bundles. In T. aestivum itforms a complete cylinder around the stelar region and alsoshows considerably more thickening of the inner tangential wallthan in the other species. The results are discussed in relation to the anatomy of theinternodal tissues and the possible function of silicon in theendodermis. Avena sativa L., Hordeum sativum Jess, Triticum aestivum L., oat, barley, wheat, silicon deposition, electron-probe microanalysis     

SURVIVAL PATTERNS IN FOUR PRAIRIE GRASSES TRANSPLANTED TO CENTRAL TEXAS

Transplanted clones of four widespread prairie grasses, Andropogon scoparius, A. gerardii, Panicum virgatum, and Sorghastrum nutans, that had survived in cultivation 1958-1962 in central Texas were studied without cultivation 1963-67 to determine survival patterns. In all four species, clones from northern and eastern sites in the United States were eliminated. Survival of A. scoparius was restricted to plants originating in central and southern Texas and in northern Mexico. Surviving clones of A. gerardii, P. virgatum, and S. nutans were chiefly of Texas origin but included other clones mostly from the south central United States. Population samples of the four species from a central Texas grassland community showed greatest survival in a multi-ramet comparison of clones originating from North Dakota to Mexico City and in a multi-clone comparison from six sites in Texas and one in New Mexico. While the superior adaptation to the local habitat by the local populations might have been expected, this study documented the survival potential of organisms in the local ecosystem.     

A simple microwave extraction method for the isolation and identification of plant opal phytoliths

We present a new extraction method for opal phytoliths, which has high potential to support qualitative analyses of the unaltered properties of single opal phytoliths. Opal phytoliths have to remain in their original solution or an equivalent to protect their amorphous (SiO₂ nH₂O) molecular structure. Fresh leaf material was heated in distilled water in a microwave oven for 3–4 hours, stirred and then strained through a plankton sieve (50-μm mesh). After purification, the plant tissue matrix was successfully degraded. Single opal phytoliths of Phragmites australis and Arundo donax as well as cell debris were isolated.