The Distribution of Silicon Deposits in the Roots of Molinia caerulea (L.) Moench. and Sorghum bicolor (L.) Moench.

The occurrence of silica in relation to meristematic zones andthe thickening of the endodermis in the roots of Molinia caerulea(L.) Moench. and Sorghum bicolor (L.) Moench. has been investigatedby means of the electron-probe microanalyser and the scanningelectron microscope. In proximal regions of mature roots ofM. caerulea, the central strengthening tissue of the stele,the vessel walls, the endodermis and the sub-epidermal sclerenchymaare areas of heavy accumulation. The distal regions of suchroots are relatively free of silicon and show little thickeningof the inner tangential walls of the endodermis or of the cellsof the strengthening tissues. The thickening of these elementsis shown to be associated with their location and the age ofthe root. In the proximal regions of S. bicolor, silicon is detected andlargely confined to the inner tangential walls of the endodermiswhich display some thickening. In addition, discrete and evenly-distributeddeposits varying in size partly fill the lumen of this layer.Some cells exhibit a number of smaller protrusions. High magnificationsof these lumen deposits show a distinct granular structure incontrast to the very uniform pattern of the wall deposits. The results are compared with deposits in grass leaves and inflorescencebracts and in woody perennials. The presence of silicon in additionto suberin, lignin and polyphenols in the thickened endodermalwall is also discussed in relation to the recognized functionof the endodermis.     

Silicon Deposition in the Roots of Hordeum sativum Jess, Avena sativa L. and Triticum aestivum L.

Electron-probe microanalysis was used to investigate the locationof silicon at the proximal end of the seminal and adventitiousroots, of almost mature field-grown specimens of Hordeum sativumJess., Avena sativa L. and Triticum aestivum L. In the seminal roots silicon was confined to the endodermis,where it was present in the thickened inner tangential and radialwalls. The outer tangential walls also contained silicon inall of the cells in wheat and in occasional cells in barleyand oats. The adventitious roots of the three cereals displayed differencesin silicon deposition. In barley, silicon was present in allthe walls of the endodermal cells, whereas in oats it was onlylocated in the inner tangential and radial walls. Wheat showedcultivar differences, no silicon was detected in Capelle Desprez,but it was present in the thickened endodermis of Little Jossand Hustler. In all the samples studied silicon was absent fromthe sub-epidermal sclerenchyma layer. The results are discussed in relation to the possible functionsof the endodermis and the signficance of silicification. Hordeum sativum Jess, barley, Avena sativa L, oat, Triticum aestivum L, wheat, silicon deposition, electron-probe microanalysis     

The Ultrastructure and Analytical Microscopy of Silicon Deposits in the Roots of Saccharum officinarum (L.)

Silicon accumulation in the endodermis of the ‘set’and ‘shoot’ roots of Saccharum officinarum (L.)were investigated by scanning electron microscopy and electron-probemicroanalysis. Silicon microassay was also carried out by meansof the Corinth analytical microscope (CORA). Aggregates arelargely associated with the inner tangential wall (ITW) of theendodermis and their formation is basically similar to thoseseen in Sorghum bicolor (L.) Moench. In contrast to Sorghumthe earliest deposits in Saccharum appear in wall strata wellwithin the cell wall cytoplasm interface. An additional layerof silicon was also located along the endodermal pericycle boundaryextending some distance along the middle lamella of the radialwalls. The results are discussed in relation to those of previous studiesof silicon accumulation in endodermal cells and to possiblefactors affecting such accumulations.     

Seminal Root Growth in Sorghum (Sorghum bicolor) Under Allelopathic Influences from Residues of Taro (Colocasia esculenta)

The length of the seminal root (SR) axis and the number andlength of lateral roots (LRs) of sorghum (Sorghum bicolor Moench)were markedly inhibited by taro [Colocasia esculenta (L.) Schott]residues incorporated into a sand growing medium. The sand profilewas divided equally into zones with and without residues. Productionand elongation of the first-order LRs of the SR axis facingthe zone containing taro residues were severely suppressed.On the side facing the zone that was free of residues, productionand elongation of LRs was not inhibited. SR and LR growth wasdrastically impaired and many plants were killed when taro residueswere incorporated in large amounts into the uppermost 2 cm ofthe growing medium. The activity of the allelopathic substancesin the root zone appeared to be location-specific. Sorghum bicolor, seminal root, lateral root, Colocasia esculenta, taro, taro residues, allelopathic substances, root growth     

The Interaction Between Silicon and Aluminium in Sorghum bicolor (L.) Moench: Growth Analysis and X-ray Microanalysis

Seeds of Sorghum bicolor (L.) Moench. were germinated on moistfilter paper for 6 d, before the seedlings were transferredto pots containing 500 µmol l^-1 Ca(NO₃)₂ for 2 d. Theseedlings were then treated with 0 or 100 µmol l^-1 Alin factorial combination with 0, 1400 or 2800 µmol l^-1Si for 8 d. The background solution used throughout was 500µmol l^-1 Ca(NO₃)₂. Aluminium treatment reduced root growthand caused a significant increase in shoot/root ratio. The presenceof silica in the solution significantly ameliorated the effectsof aluminium on root growth. Three treatment were selected for a microanalytical investigationof the basal region of the root: 2800 µmol l^-1 Si only;100 µmol l^-1 Al only; and a combination of the two. Inthe 2800 µmol l^-1 treatment silica was deposited in theendodermis, with the greatest accumulation being in the innertangential wall (ITW). When plants were treated with 100 µmoll^-1 Al only, aluminium concentration was highest in the outertangential wall (OTW) of the epidermis. The element was presentin the hypodermal walls and OTW of the endodermis and was notdetectable in the stele. With both 2800 µmol l^-1 Si and100 µmol l^-1 Al in the nutrient solution the two biomineralizationsites were the ITW of the endodermis, where silicon was themajor element deposited, and atypically in the OTW of the epidermiswhere both aluminium and silicon were present. The sequestrationof aluminium in the Al-Si deposit in the OTW of the epidermismay represent the mechanism that allows greater root growthin this treatment.Copyright 1993, 1999 Academic Press Sorghum bicolor (L.) Moench., aluminium, silicon, calcium, root, toxicity, biomineralization, X-ray microanalysis, freeze substitution     

The Ultrastructure and Analytical Microscopy of Silicon Deposition in the Intercellular Spaces of the Roots of Molinia caerulea (L.) Moench

Silicon accumulation in mature roots of Molinia caerulea (L.)Moench. was investigated by transmission electron and Cora analyticalmicroscopy. Deposits are located in the intercellular spaces(ICS) of the persistent cortical cells immediately externalto the endodermis. The earliest deposits are in the form ofspheres lining the cavities and are followed by further depositswhich eventually fill the ICS. Evidence is presented that priorto and during the earliest silicon formations, many ICS revealedthe presence of cell organelles. No silicon was detected inthe inner tangential walls of the endodermis. The results are discussed in relation to previous studies ofsilicon deposits in the roots of Molinia and to possible pathwaysresulting in deposits associated with the ICS. Molinia caerulea(L.) Moench, roots, silicon deposition, analytical microscopy     

Silicon-induced changes in viscoelastic properties of sorghum root cell walls

Silicon is deposited in the endodermal tissue in sorghum (Sorghum bicolor L. Moench) roots. Its deposition is thought to protect vascular tissues in the stele against invasion by parasites and drying soil via hardening of endodermal cells. We studied the silicon-induced changes in mechanical properties of cell walls to clarify the role of silicon in sorghum root. Sorghum seedlings were grown in nutrient solution with or without silicon. The mechanical properties of cell walls were measured in three separated root zones: basal, apical and subapical. Silicon treatment decreased cell-wall extensibility in the basal zone of isolated stele tissues covered by endodermal inner tangential walls. The silicon-induced hardening of cell walls was also measured with increases in elastic moduli (E) and viscosity coefficients (eta). These results provided new evidence that silicon deposition might protect the stele as a mechanical barrier by hardening the cell walls of stele and endodermal tissues. In contrast to the basal zone, silicon treatment increased cell-wall extensibility in the apical and subapical zones with concomitant decrease in E and eta. Simultaneously, silicon promoted root elongation. When root elongation is promoted by silicon, one of the causal factors maybe the silicon-enhanced extensibility of cell walls in the growing zone.     

Silicification in sorghum (Sorghum bicolor) cultivars with different drought tolerance

Sorghum belongs to a group of economically important, silicon accumulating plants. X-ray microanalysis coupled with environmental scanning electron microscopy (ESEM) of fresh root endodermal and leaf epidermal samples confirms histological and cultivar specificity of silicification. In sorghum roots, silicon is accumulated mostly in endodermal cells. Specialized silica aggregates are formed predominantly in a single row in the form of wall outgrowths on the inner tangential endodermal walls. The density of silica aggregates per square mm of inner tangential endodermal cell wall is around 2700 and there is no significant difference in the cultivars with different content of silicon in roots. In the leaf epidermis, silicon deposits were present in the outer walls of all cells, with the highest concentration in specialized idioblasts termed 'silica cells'. These cells are dumb-bell shaped in sorghum. In both the root endodermis and leaf epidermis, silicification was higher in a drought tolerant cultivar Gadambalia compared with drought sensitive cultivar Tabat. Silicon content per dry mass was higher in leaves than in roots in both cultivars. The values for cv. Gadambalia in roots and leaves are 3.5 and 4.1% Si, respectively, and for cv. Tabat 2.2 and 3.3%. However, based on X-ray microanalysis the amount of Si deposited in endodermal cell walls in drought tolerant cultivar (unlike the drought susceptible cultivar) is higher than that deposited in the leaf epidermis. The high root endodermal silicification might be related to a higher drought resistance.     

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.     

Nitrate Reductase Activity: A Biochemical Criterion of Hybrid Vigour in Sorghum bicolor (L.) Moench

F₁ hybrids of Sorghum bicolor (L.) Moench and their inbred parentswere analysed for NADH-nitrate reductase activity during theearly stages of seedling growth. In all the hybrids both mid-parentaland better parental heterosis were discernible in shoots whereasin roots two hybrids out of the three tested, showed heteroticlevels. It is suggested that in sorghum nitrate reductase activityduring seedling stages can be used as a biochemical criterionfor evaluating hybrid vigour. Sorghum bicolor (L.) Moench, sorghum, hybrid vigour, nitrate reductase     

Biochemical Basis of Heterosis in Sorghum: Changes in Chlorophylls and Ascorbic Acid Turnover during Seedling Growth

Shoots of three F1 hybrids of Sorghum bicolor (L.) Moench withtheir inbred parents were analyzed for chlorophyll a and chlorophyllb contents as well as for ascorbic acid turnover during theearly stages of seedling growth. In all the hybrids both chlorophylland ascorbic acid turnover showed better-parental and/or mid-parentalheterosis. Since ascorbate participates in photosynthesis andnitrate reduction, it is suggested that a well co-ordinatedsystem incorporating photosynthetic efficiency and nitrate assimilationmay be associated with the manifestation of hybrid vigour insorghum. Sorghum bicolor (L.) Moench, hybrid vigour, chlorophyll, ascorbic acid, nitrate reductases     

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     

Inhibition of Anthocyanin Synthesis by Cobaltous Ions in the First Internode of Sorghum bicolor L. Moench

Cobaltous ions (Co²⁺) inhibited light-mediated anthocyanin synthesisin excised first internodes of Sorghum bicolor (L.) Moench.Studies with precursors/intermediates of the anthocyanin biosyntheticpathway, such as acetate, phenylalanine, t-cinnamic acid, tyrosine,and p-coumaric acid were undertaken to identify the metabolicsite at which Co²⁺ ions inhibit anthocyanin synthesis. p-Coumaricacid partially restored anthocyanin synthesis. No other intermediatewas effective in bringing about recovery. It is suggested thatCo²⁺ might interfere with process/es which leads to the formationof p-coumaric acid, an intermediate of the anthocyanin biosyntheticpathway. Key words: Sorghum bicolor (L.) Moench, anthocyanin, cobaltous ions, phenylalanine ammonia-lyase     

SILICON IN THE ROOTS OF HIGHER PLANTS

Silicon (Si) distribution in the roots of Sorghastrum nutans (L.) Nash and Sorghum bicolor (L.) Moench. was investigated by means of the electron-probe microanalyzer and scanning electron microscope. In both species, Si was confined to the inner tangential wall of the tertiary-phase endodermal cells in the form of nodular silica aggregates of similar morphology and X-ray intensity. The results are compared to those for six closely related genera, as well as to studies of Si in the roots of species of other tribes of the family Poaceae. The various types of root deposits occurring in the family are described, and their relationships discussed. It is concluded that the type of Si distribution exhibited is determined largely by the phylogenetic status of the genus, rather than by the basic pattern of root anatomy.     

Sorghum Seedling Growth as a Function of Sodium Chloride Salinity and Seed Size

Sodium chloride salinity in the range 0–90 mM inhibitedgrowth of sorghum seedlings. Seedlings derived from small seedswere most sensitive to salinity. Salinity, seed size, seedling growth, sorghum, Sorghum bicolor L. Moench     

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     

Viability and Germination of the Pollen of Sorghum [Sorghum bicolor (L.) Moench]

Previous studies have demonstrated that pollen of sorghum [Sorghumbicolor (L.) Moench] loses capacity to both germinate in vitroand to set seed in vivo soon after being shed. The current studyevaluates the capacity for dehydrated pollen to effect in vitrogermination, reduce tetrazolium chloride, and set seed on cytoplasmicmale sterile plants. Morphological changes during pollen germinationwere examined by scanning electron microscopy (SEM). Close to70% of the pollen germinated in 5 min, or less, when collectedat 80% relative humidity (RH) and stored in sealed glass vials.Pollen tubes elongated autotropically with atmospheric humidityapparently being a controlling factor in the process. Pollendehydrated at 50% RH and 25°C for 15-30 min neither germinatedin vitro, reduced tetrazolium chloride, nor set seed on malesterile plants. Rehydrating the pollen did not restore the capacityfor germination. SEM micrographs demonstrated that elongatingpollen tubes encircled the pollen grain and were contiguousto the surface. A fibrillar-like material existed on the exineof separated pollen grains at the point where the grains hadbeen previously attached.Copyright 1994, 1999 Academic Press Sorghum pollen, germination, seed-set, viability, scanning electron microscopy, Sorghum bicolor (L.) Moench     

Time Lapse Analysis of Root Elongation Rates of Rice and Sorghum During the Day and Night

This paper describes a technique to monitor the root elongationrate (RER) per hour for several days, and variation in RER duringthe day and night. Rice (Oryza sativaL.) and sorghum (SorghumbicolorMoench) were grown in root boxes placed inside a growthchamber set at 25 °C with a 12 h photoperiod. Seminal rootaxes were sandwiched between a transparent acrylic board andfilter paper placed on a loamy sand soil. The roots were photographedunder dim green light using a CCD camera connected to a timelapse video recorder. The environment of the root, includingtemperature, light, nutrient, water and air supply, was controlledprecisely and maintained constant. RER fluctuated hourly insorghum and to a greater extent in rice. Maximum RERs were 1.4to 4.4 times faster than minimum rates. RERs during the dayand night did not differ statistically when temperatures werethe same.Copyright 1998 Annals of Botany Company Oryza sativaL., periodicity, root elongation,Sorghum bicolorMoench, time lapse.     

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     

Application of silicon improves salt tolerance through ameliorating osmotic and ionic stresses in the seedling of Sorghum bicolor

Silicon has been widely reported to have a beneficial effect on improving plant tolerance to biotic and abiotic stresses. However, the mechanisms of silicon in mediating stress responses are still poorly understood. Sorghum is classified as a silicon accumulator and is relatively sensitive to salt stress. In this study, we investigated the short-term application of silicon on growth, osmotic adjustment and ion accumulation in sorghum (Sorghum bicolor L. Moench) under salt stress. The application of silicon alone had no effects upon sorghum growth, while it partly reversed the salt-induced reduction in plant growth and photosynthesis. Meanwhile, the osmotic potential was lower and the turgor pressure was higher than that without silicon application under salt stress. The osmolytes, the sucrose and fructose levels, but not the proline, were significantly increased, as well as Na⁺ concentration was decreased in silicon-treated plants under salt stress. These results suggest that the beneficial effects of silicon on improving salt tolerance under short-term treatment are attributed to the alleviating of salt-induced osmotic stress and as well as ionic stress simultaneously.