An Ultrastructural Study on the Developmental Phases and Silicification of the Glumes of Phalaris canariensis L.

In the glume of Phalaris canariensis L. silicon deposition takesplace in the macrohairs, papillae, prickle hairs and silicacells of the abaxial epidermis before panicle emergence. Early in their development the macrohairs have large vacuolesand thin walls. At maturity the walls become thickened and aremajor sites of silica deposition. Dry ashing reveals a helicalpattern within the hair walls. Distinct papillae and prickle hairs were first observed oneweek before panicle emergence. Here silicification was initiallyconfined to outer tangential walls, but by two weeks after emergencetheir cytoplasmic contents had broken down, and the lumina werefilled with siliceous granules. Cork-silica twin cells werealso present in the abaxial epidermis. By panicle emergencethe silica cells were infilled, but the cork cells retainedtheir cytoplasmic contents. The long cells of the abaxial epidermiswere initially thin walled, but thickening occurred in the outertangential wall, this being complete by one week after emergence.These cells remained relatively unsilicified throughout. After panicle emergence the adaxial epidermal cells, and theirassociated parenchyma cell layers began to lose their cellularcontents and collapse. This process was complete two weeks afteremergence when the collapsed walls formed a thin internal layerbetween the two epidermi. Electron opaque granular material,containing several elements, but predominantly calcium, waspresent between the collapsed cell walls. The results are comparedwith those for the lemma, and silica deposition mechanisms arealso discussed. Phalaris canariensis L., canary grass, silicification, trichome, glume, ultrastructure     

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.     

Silicon Deposition in the Roots, Culm and Leaf of Phalaris canariensis L

Silicon deposition in the roots, culm and leaf of canary grass(Phalaris canariensis L.) was investigated using light microscopy,scanning electron microscopy and electron probe microanalysis. In adventitious roots grown in solution silicon was concentratedin four endodermal walls. Silicon was not detected in the endodermisof aerial adventitious roots, but was present in the epidermisand outer cortical cell layers. Silicon deposition in the culm mainly took place in the epidermis,and particularly in epidermal papillae. The silica deposition pattern in the leaf was typical of thesub-group Festucoideae. The leaf blade showed deposits in costalprickle hairs and wavy rods, but few intercostal deposits. Inthe ligule deposition was confined to isolated groups of pricklehairs on the abaxial surface. The major sites of silica depositionin the leaf sheath were the stomatal subsidiary cells, papillaeand intercostal idioblasts. Prickle hairs were much less commonin the sheath than the blade, and costal wavy rods appearedto be absent in the sheath. Phalaris canariensis L., canary grass, silicification, root, culm, leaf, electron probe microanalysis     

Silicon Deposition in the Inflorescence Bristles and Macrohairs of Setaria italica (L.) Beauv.

Silicon deposits in the inflorescence bristles subtending eachspikelet, and in the macrohairs of foxtail millet (Setaria italica(L.) Beauv.) were investigated using scanning electron microscopyand electron-probe microanalysis. High concentrations of silicon were detected in the pricklehairs which covered the bristles. In the unicellular macrohairscovering the inflorescence axis and its branches, silicon wasdeposited along the whole length of the hairs. The mechanisms by which silicification may have taken place,and the possibility that the bristles and macrohairs are involvedin the aetiology of oesophageal cancer in N. China are discussed. Setaria italica (L.) Beauv., foxtail millet, millet, silicon deposits, silicification, prickle hairs, scanning electron microscopy, electron-probe microanalysis     

Morphogenesis of Female Reproductive Organs in Carpinus turczaninowii and Ostryopsis davidiana (Betulaceae)

For better understanding of the relationships between genera, the primordium occurrence and morphological developmental process of female inflorescence, cymule and floret in Carpinus turczaninowii Hance and Ostryopsis davidiana Decne. of the Betulaceae were observed under the scanning electron microscope (SEM). Both species were monoecious. Their female inflorescence was a compound spike comprising several cymules arranged helically along an inflorescence axis. Each cymule consisted of two florets and five bracts, i.e., one primary bract and four other secondary ones which were developed from two semi-circular common primordia, respectively. In Carpinus , the adaxial secondary bracts grew slowly, while the abaxial ones grew fast, resulting in the appearance of a wide leafy bract upon maturity. In Ostryopsis , however, both abaxial and adaxial secondary bracts were fully developed, becoming a bladder-like but unclosed involucre when mature. Perianth primordia in both genera were circular. When the ovary became larger and larger, the perigone grew gradually, and finally surrounded and was adnate to the ovary. Some traditional viewpoints on the number of bracts and the orientation of bicarpellate ovary in cymule were clarified based on this study. The cymule bracts were not so many as those observed by Abbe; and the two bicarpellate ovaries were orientated perpendicularly, rather than parallel.     

鹅耳枥和虎榛子（桦木科）雌性生殖器官的形态发生

为了进一步理解类群之间的系统发育关系,在扫描电镜下,对桦木科植物鹅耳枥（Carpinus turczaninowii Hance)和虎榛子（Ostryopsis davidiana Decne.)的雌花序、小花序和雌花的原基形成和发育过程进行了观察。两种植物均具单性花、雌雄同株。其雌花序为复合的穗状花序,每两朵小花构成一个小聚伞花序,多个这样的小花序螺旋排列在一个总花序轴上。小花序由5枚苞片组成,1枚初级苞片,4枚次级苞片。后分别由两个半环状的共同原基发育而来。鹅耳枥的近轴面次级苞片生物缓慢,远轴面的生长较快,成熟时呈扩展的叶片状;虎榛子的近轴面和远轴面次给苞片均生长较快,成熟时靠全呈囊状。花被原基为环状,花被随着子房的发育而而逐渐长大包围子房并与之愈合。研究对前人有关小花序的苞片数目和两个二心皮子房的定位方式等方面的认识作了澄清或纠正。每个小花序的苞片数目不像Abbe观察的那么多;二心皮子房定位方式在鹅耳枥属是互成直角,而非相互平行。     

ELECTRON PROBE MICROANALYSIS OF SILICON DEPOSITION IN THE INFLORESCENCE BRACTS OF THE RICE PLANT (ORYZA SATIVA)

The deposition of silicon in tissues of the inflorescence bracts of rice has been studied with the electron probe microanalyzer. Tissues for analysis were prepared by means of peels, frozen transverse and longitudinal sections, chromations and macerations. The microanalysis shows the heaviest deposition in a layer external to the abaxial (outer) epidermis. The cells of this epidermis are only sparsely silicified, but the’ imprints of these cells are left on the outer silica layer. In the inner tissues of the bracts, silicon deposition is mostly associated with the cell walls.     

Silica Distribution in the Caryopsis and Inflorescence Bracts of Foxtail Millet [Setaria italica (L.) Beauv.] and its Possible Significance in Carcinogenesis

Silicon deposits in the caryopsis and inflorescence bracts offoxtail millet [Setaria italica (L.) Beauv.] were investigatedusing light microscopy, scanning electron microscopy and electronprobe microanalysis. The samples were obtained from Lin Xian,Henan province, northern China and CSIRO, Australia. High concentrations of silicon were observed in the papillaeon the external surfaces of the inflorescence bracts, and inthe epidermal cells. In the caryopsis silicon was depositedin the aleurone layer. Silicification was heavier in the LinXian samples. The heavy accumulation of silica in the foxtail millet and thepossibility that fragments of plant silica may be implicatedin the aetiology of oesophageal cancer in the Lin Xian regionare discussed. Setaria italica (L.), Beauv, foxtail millet, caryopsis, silica distribution, scanning electron microscopy     

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     

SCANNING ELECTRON MICROSCOPY AND ELECTRON MICROPROBE ANALYSIS OF SILICIFICATION PATTERNS IN INFLORESCENCE BRACTS OF AVENA SATIVA

Using scanning electron microscopy, we determined the kinds and distribution of epidermal cell types in Avena inflorescence bracts (glume, lemma, and palea). Electron microprobe analysis of silica deposition in these epidermal cells showed that silica cells constitute one of the important deposition sites. Probe ratio data indicate that the silica deposited is 74 % pure. Significant amounts of silica also become deposited in the trichomes and lesser amounts in the walls of long epidermal cells. None could be detected in the stomata. The possible functional significance of silica deposition in epidermal cells of these bracts is discussed.     

Developmental analysis of teosinte glume architecture1: A key locus in the evolution of maize (Poaceae)

A key event in the evolution of maize from teosinte was a reduction in the cupulate fruitcase and softening of the glumes, which increased the accessibility of kernels for harvest. The teosinte glume architecture1 (tga1) locus largely controls this difference between maize and teosinte, and thus may have played a pivotal role in maize evolution. The teosinte allele (tga1+teosinte) lengthens inflorescence internodes, shortens rachillae, and makes glumes longer, thicker, and harder. Developmental characterization of morphometric traits reveals that differences among genotypes are apparent early in female inflorescence development. Increased hardening in glumes homozygous for tga1+teosinte is correlated with a thicker abaxial mesoderm of lignified cells. Silica deposition in the abaxial epidermal cells of the glumes is also affected. In the maize background, glumes homozygous for tga1+teosinte deposit silica in both the short and long cells of the glume epidermis, whereas glumes homozygous for the maize allele (Tga1+Maize) concentrate silica only in the short cells. Silica deposition also appears to be affected by genetic background. The effects of tga1 appear largely to explain the differences in glume induration between maize and teosinte. The diverse pleiotropic effects of tga1 suggest that it is regulatory in nature.     

Genotypic Variation in the Thickness of Silica Deposition on Flowering Rice Spikelets

Silicon may play an important role in regulating the transpirationrate of rice (Oryza sativa L.), particularly cuticular transpiration.The control of cuticular transpiration is important in ricespikelets because water stress at anthesis may severely disruptfertility and grain yield. Data on the quantitative variationamong rice cultivars in the thickness of the silica layer ofthe flowering spikelet were obtained in order to assess thepotential for genetic selection for silica layer thickness asa potential means for increasing spikelet resistance to waterloss. Flowering spikelets were collected from 17 genotypes and thicknessmeasurements were made of the major anatomical layers in crosssection. The silica layer of the lemma varied from 42 to 177µm among cultivars. Similar variation was observed inthe palea. Differences among cultivars were also found in thethickness of the epidermis and sclerenchyma-parenchyma layer. The total cross-sectional thickness of the lemma and palea averagedslightly over 100 µm. Total thickness was not significantlycorrelated with the length, width or product of length width.Thickness of silica deposition was significantly correlatedwith spikelet length width suggesting that these easily measuredparameters may be useful in screening for silica thickness. Oryza sativa L., rice, panicle, silicon, lemma, palea, husk     

狗牙根花序发育过程的形态学观察

对狗牙根(Cynodon dactylon‘C299’)花序发育过程中的形态学变化进行了观察。结果表明,‘C299’花序的整个发育过程可分为8个阶段,即营养生长期、穗轴发生期、苞叶原基分化期、小穗原基分化期、小穗分化期、小花分化期、颖片和内外稃发育期及花药和柱头形成期。其中,穗轴发生期(直立茎上有6~9片叶)是抑制花序形成和决定种子产量的关键时期。     

Floral Development in Sonja White Clover (Trifolium repens) a Papilionoid Legume

Floral development in Sonja white clover was examined usingscanning electron microscopy. Florets and bracts were foundto arise from common primordia initiated as protuberances fromthe apical meristematic area of the inflorescence. The patternof floret initiation on the inflorescence was acropetal, theoldest florets resting basally. Floral organ initiation withineach floret was acropetal, petals being initiated before stamens.Floret development was zygomorphic, each whorl of floral organsdeveloping unidirectionally from the abaxial side. There wasfound to be overlapping in the timing of initiation and developmentof these organs. Antesepalous stamens were found initially tooutgrow their antepetalous counterparts. Early petal developmentwas synpetalous. Eglandular hairs were found basally on thecalyx cup and on the pedicel. Procumbent hairs were found tobe more numerous and randomly distributed on the abaxial surfacesof the mature calyx cup. Trifolium repens L., Sonja cultivar, white clover, scanning electron microscopy, floral development, inflorescence     

Selective light transmittance of translucent bracts in the Himalayan giant glasshouse plant Rheum nobile Hook. f. & Thomson (Polygonaceae)

Translucent bract transmittance of ultraviolet (UV) to infrared (IR) radiation (between 320 and 800 nm) and leaf anatomy were examined in a glasshouse plant, Rheum nobile Hook. f. & Thomson (Polygonaceae) to assess the function of avoiding injury by UV radiation while keeping the inflorescence warm by photosynthetically active (PA) and IR radiation. Although the translucent bracts and rosulate leaves transmitted little UV radiation, the former always transmit more PA and IR radiation. Additionally, the bracts transmit much more scattered solar radiation than direct radiation. The bracts are also anatomically different from the rosulate leaves. They have two or three layers of mesophyll cells with neither palisade nor spongy parenchymatous cells; in addition, the uppermost layer of mesophyll and the epidermis stain easily, and both are thought to play a role in attenuating UV radiation. The leaf epidermis of many land plants has UV absorbing pigments such as flavonoids, which absorb almost all UV radiation. Thus the role of the bracts of R. nobile is to protect the reproductive organs by absorbing UV radiation and to keep them warm by transmitting PA and IR radiation. The bracts are believed to have adapted function and form to the environment, in particular, to the weather conditions of the eastern Himalaya.     

MADS-box gene expression and implications for developmental origins of the grass spikelet

Basic questions regarding the origin and evolution of grass (Poaceae) inflorescence morphology remain unresolved, including the developmental genetic basis for evolution of the highly derived outer spikelet organs. To evaluate homologies between the outer sterile organs of grass spikelets and inflorescence structures of nongrass monocot flowers, we describe expression patterns of APETALA1/FRUITFULL-like (AP1/FUL) and LEAFY HULL STERILE-like (LHS1) MADS-box genes in an early-diverging grass (Streptochaeta angustifolia) and a nongrass outgroup (Joinvillea ascendens). AP1/FUL-like genes are expressed only in floral organs of J. ascendens, supporting the hypothesis that they mark the floral boundary in nongrass monocots, and JaLHS1/OsMADS5 is expressed in the inner and outer tepals, stamen filaments and pistil. In S. angustifolia, SaFUL2 is expressed in all 11 (or 12) bracts of the primary inflorescence branch, but not in the suppressed floral bract below the abscission zone. In contrast, SaLHS1 is only expressed in bracts 6-11 (or 12). Together, these data are consistent with the hypotheses that (1) bracts 1-5 of S. angustifolia primary inflorescence branches and glumes of grass spikelets are homologous and that (2) the outer tepals of immediate grass relatives, bracts 6-8 of S. angustifolia, and the lemma/palea are homologous, although other explanations are possible.     

MORPHOGENESIS OF CAPITATE GLANDULAR HAIRS OF CANNABIS SATIVA (CANNABACEAE)

The glandular secretory system in Cannabis sativa L. (marihuana) consists of three types of capitate glandular hairs (termed bulbous, capitate-sessile, and capitate-stalked) distinguishable by their morphology, development, and physiology. These gland types occur together in greatest abundance and developmental complexity on the abaxial surface of bracts which ensheath the developing ovary. Bulbous and capitate-sessile glands are initiated on very young bract primordia and attain maturity during early stages of bract growth. Capitate-stalked glands are initiated later in bract growth and undergo development and maturation on medium, to full sized bracts. Glands are epidermal in origin and derived, with one exception, from a single epidermal initial. The capitate-stalked gland is the exception and is of special interest because it possesses a multicellular stalk secondarily derived from surrounding epidermal and subepidermal cells. Glands differentiate early in development into an upper secretory portion and a subtending auxiliary portion. The secretory portion, depending on gland type, may range from a few cells to a large, flattened multicellular disc of secretory cells. The secretory portion produces a membrane-bound resinous product which caps the secretory cells. Capitate-stalked glands are considered to be of particular evolutionary significance because they may represent a gland type secondarily derived from existing capitate-sessile glands.     

Epidermal Structure in the Ligule of Rice (Oryza sativa L.)

The structure of the abaxial epidermis of the ligule of rice(Oryza sativa L.) as seen in the light and scanning electronmicroscope is described. Long cells, silica cells, cork cells,prickle hairs, microhairs and stomata-like structures were found.Reasons for considering these latter structures to be true stomataare given. Results of an X-ray analysis for silicon are presentedand the distribution of silica discussed in relation to itsfunctional role in the ligule. Oryza sativa L, rice, Gramineae, ligule, epidermis, scanning electron microscopy, X-ray analysis, silica, stomata     

Flowering and apical meristem growth dynamics

The shoot apical meristem generates stem, leaves, and lateralshoot meristems during the entire shoot ontogeny. Vegetativeleaves are generated by the meristem in the vegetative developmentalphase, while in the reproductive phase either bracts subtendinglateral flower primordia (or paraclades), or perianth and strictlyreproductive organs are formed. Meristem growth is fully characterizedby the principal growth rates, directions, volumetric, and arealgrowth rates. Growth modelling or sequential in vivo methodsof meristem observation complemented by growth quantificationallow the above growth variables to be estimated. Indirectly,growth is assessed by cell division rates and other cell cycleparameters. Temporal and spatial changes of growth and geometrytake place at the meristem during the transition from the vegetativeto the reproductive phase. During the vegetative phase, meristemgrowth is generally indeterminate. In the reproductive phaseit is almost always determinate, but the extent of determinacydepends on the inflorescence architecture. In the vegetativephase the central meristem zone is the slowest growing region.The transition from the vegetative to the reproductive phaseis accompanied by an increase in mitotic activity in this zone.The more determinate is the meristem growth, the stronger isthis mitotic activation. However, regardless of the extent ofthe activation, in angiosperms the tunica/corpus structure ofthe meristem is preserved and therefore the mitotic activityof germ line cells remains relatively low. In the case of thethoroughly studied model angiosperm plant Arabidopsis thaliana,it is important to recognize that the flower primordium developsin the axil of a rudimentary bract. Another important featureof growth of the inflorescence shoot apical meristem is theheterogeneity of the peripheral zone. Finally, the role of mechanicalfactors in growth and functioning of the meristem needs furtherinvestigation. Key words: Flower primordium, geometry, growth, inflorescence, shoot apical meristem, transition from vegetative to reproductive phase Received 4 October 2007; Revised 5 November 2007 Accepted 6 November 2007     

Lemma micromorphological characters in the Chloridoideae (Poaceae) optimized on a molecular phylogeny

Eight lemma micromorphological characters of 83 taxa representing 61 genera in the Chloridoideae have been investigated using Scanning Electron Microscopy, including long cells, cork cells, stomata, bicellular microhairs, papillae, silica cells, microprickles, and macrohairs. Five new types of lemma micromorphological characters were reported here. Data for 27 taxa representing 19 genera from previous publications were also supplied to access the homology of lemma micromorphological characters for different groups through optimization onto a molecular cladogram. Given the optimization, five characters including long cells, cork cells, stomata, papillae, microprickles are of phylogenetic significance for supra-generic groups. Seven characters including straight outline long cells, crescent-shaped cork cells, absent stomata, absent papillae, dumb-bell-shaped silica cells, c-type microprickles, and papillate-base macrohairs may not be homologous, however, the enneapogonoid-type bicellular microhairs appeared as a synapomorphy for the Chloridoideae.