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     

Origin of Epidermis and Development of Root Primordia in Pistia, Hydrocharis and Eichhornia

All three floating plants have roots bearing laterals derivedfrom both pericycle and endodermis. In Pistia and Eichhornialaterals arise within the meristem of the mother root; in Hydrocharisthey arise from mature tissue. In Pistia and Hydrocharis theepidermis becomes anatomically discrete between cortex and cap:in Pistia it is derived from the endodermis of the mother root,in Hydrocharis from the pericycle. The epidermis is not discretein Eichhornia and is derived from the pericycle of the motherroot with the cortex. Stathmokinetic data were used to construct timetables of developmentwhich show how the differences arise. In Pistia the first periclinaldivision of the endodermis-derived tissue individualizes theepidermis and occurs early, before a quiescent centre forms.In Hydrocharis the epidermis also becomes discrete before thepole of the meristem becomes quiescent, but it does so by apericlinal division of the pericycle-derived tissue. In Eichhorniapericlinal divisions occur in the outermost layer of the pericycle-derivedtissue long after quiescence has set in at the pole and afterthe fourth periclinal division in the endodermis derived cap.Its epidermis therefore never becomes anatomically discretethough it becomes functionally discrete because its polar cellsstop dividing as in the other plants. The involvement of the endodermis of mother roots in the formationof laterals is discussed in relation to the state of differentiationat sites of primordium formation, discreteness of the epidermisand subsequent fate of primordia. Pistia stratiotes L., Hydrocharis morsus-ranae L., Eichhornia crassipes Solms., primordia, lateral root, discrete epidermis, development, chimera, stathmokinetics     

Distribution and Accumulation of Thiophenes in Plants and Calli of Different Tagetes Species

The diversity of thiophenes (natural biocides) and the differencesbetween the concentrations of these compounds in the leavesand roots of Tagetes erecta L., T. patula L. cv. Nana furia,and T. minuta L. (marigolds) indicated the presence of at leasttwo different sites of accumulation: leaves and roots. Leafexplants of Tagetes, however, are used by preference to obtaincallus cultures. Once subcultured, secondary (C₂) calli of T.patula obtained from leaves of 4 to 7-week-old plants, containedhigher amounts of accumulated thiophenes (up to 80% of the amountsin the leaves) than original (C₁) or twice subcultured calli(C₃). The concentrations of thiophenes in C₂ calli of T. minutawere about half those of C₁ calli, while the concentrationsof thiophenes of C₁ calli amounted to 1-2% of the leaf values.Most of the C₃ calli of T. minuta did not contain thiophenesat all. Although C₁ calli of T. erecta also contained considerableamounts of thiophenes, the C₂ calli died, most likely owingto high levels of accumulated polyphenolic compounds. The combinationof species effects and the physiological state of plants andcalli provides adequate information to decide whether Tagetescalli are able to produce thiophenes or not. It is concludedthat the ability to produce thiophenes does not depend on theorgan used, but on the genetic information present in the species,and on the physiological state of plants and calli, particularlytheir age. Key words: Callus, explant selection, Tagetes erecta, Tagetes minuta, Tagetes patula, thiophenes     

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     

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     

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.     

Comparative Requirement for Endogenous Ethylene during Seed Germination

Requirement for endogenous ethylene during seed germinationof the following ten species was determined: Lycopersicon esculentumMill, (tomato), Allium cepa L. (onion), Avena fatua L., dormantpure line AN-51 (wild oats), Cucumis sativus L. (cucumber),Sinapis arvensis L. (wild mustard), Tagetes erecta L. (marigold),Raphanus sativus L. (radish), Triticum aeslivum L. (wheat),Catharanthus roseus L. (periwinkle), and Phaseolus aureus L(mung bean). Experiments were done under controlled conditionssuited for the germination of each species. Criteria used todetermine the need for endogenous ethylene were: (i) temporalrelationship between ethylene production and seed germination;(ii) parallel inhibition of ethylene synthesis and seed germinationby L-     

The Relationship Between Lateral-Root Distribution and Endodermis and Pericycle Cell Length in Allium cepa L. Adventitious Roots

Endodermis and pericycle cell lengths were measured in intactand decapitated adventitious roots of Allium cepa L. Decapitationhad no effect on cell length in mature portions of the root,although it affected more immature cells, impeding normal elongation.Cell length shows a characteristic pattern in different zonesof the adventitious root: cells in the medial region were moremarkedly elongated. The number of lateral root primordia wasalso determined in different zones of the adventitious root.The possible relationship between lateral root distributionpattern and cell length in the endodermis and pericycle is discussed. Allium cepa, onion, endodermis, pericycle, lateral root, cell length     

The Effect of Sulphur Dioxide on the Growth of Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerata L., and Phleum pratense L.

Lockyer, D. R. 1985. The effect of sulphur dioxide on the growthof Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerataL., and Phleum pratense L.?J. exp. Bot. 36: 1851-1859. Fouragriculturally important grasses, Lolium perenne L., Loliummultiflorum Lam., Dactylis glomerata L. and Phleum pratenseL. were exposed to sulphur dioxide (SO₂) in a system of exposurechambers. The plants were exposed for a total of 43 d to meanconcentrations of SO₂ in the air of 0,87 or 448 (µg m^–3and herbage was harvested twice. All four grasses showed chloroticlesions after exposure to the highest concentration of SO₂.The effect of SO₂ on the yield of herbage was statisticallysignificant only at the second harvest and at the highest concentration;the dry weights of shoots of D. glomerata and L. perenne werereduced by 33% and 16% respectively. Significant effects ofSO₂ were also found on the 'transpiration coefficients' measuredfor D. glomerata and P. pratense. The grasses differed in theiruptake of sulphur from the atmosphere but this was not relatedto their sensitivity to SO₂. Total–S concentration inthe shoots of L. perenne, L. multiflorum and D. glomerata increasedalmost linearly in response to increasing SO₂ concentration;with P. pratense only the highest SO₂ concentration raised total-Sabove the level in control plants. These increases were almostentirely due to the accumulation of sulphate–S. Key words: Sulphur diozide, Lolium perenne, Lolium multiflorum, Dactylis glomerata, Phleum pratense     

Root Cell Ultrastructure in Developing Aerenchyma Tissue of Three Wetland Species

Patterns of root cortex cell development and ultrastructurewere analysed in Sagittaria lancifolia L., Thalia geniculataL. and Pontederia cordata L. using scanning and transmissionelectron microscopy (SEM, TEM). In all three species, cortexcells were arranged in radial columns extending from the endodermisto the hypodermis/epidermis. During gas space formation, thecortex cells elongated parallel to the root radius and shrankin the plane perpendicular to the radius leaving long and thinrows of cortex cells extending from the endodermis to the epidermis.Although the cortex cells appeared collapsed in tissue withwell-developed gas spaces, TEM revealed that the cortical cellsas well as the epidermal cells maintained intact membranes andmany normal organelles. Formation of root cortex tissue withwell-developed gas spaces does not require cell death in thesespecies. Living cortex cells in root tissue with mature gasspaces could provide a symplastic pathway for transport betweenthe root stele and the living epidermal cells. Copyright 2000Annals of Botany Company Sagittaria lancifolia, Thalia geniculata, Pontederia cordata, aerenchyma, root, wetland, development     

Reserve Mobilization During Germination of Tagetes minuta L.

Levels of albumins, globulins and starch were measured in dryTagetes minuta L. achenes (seeds) germinating at 25 °C andin those thermo-inhibited at 35 °C. In addition, the compositionof amino acids, fatty acids and free sugars was determined. In germinating seeds, albumins increased, while globulins decreased.At 35 °C, only a delayed decrease in globulins occurred.However, in both, the amino acids serine and glutamate increased.Lipid composition remained constant except for a slight declinein linoleic acid in the germinating seeds. At 25 °C, starchlevels increased with time while at 35 °C, there was onlya transient increase. Sucrose was the major free sugar foundin the seeds at all times, but its levels declined in the germinatingseeds. This was accompanied by an increase in the proportionsof glucose and fructose. No such changes in sugar compositionwere observed in the thermo-inhibited seeds. Tagetes minuta L., seed germination, reserve mobilization, thermo-inhibition     

A Comparative Study of the Haustorial Development of Striga asiatica (L.) Kuntze on Sorghum Cultivars

Ten sorghum cultivars were studied for their mode of Strigaparasitization, and the factors conferring resistance in resistantcultivars most of the Striga haustona failed to penetrate beyondthe endodermis, whereas in susceptible cultivars the haustonapenetrated the endodermis and became established Resistant cultivars showed marked endodermal and pencyclic thickeningand the deposition of silica in their endodermal cells, whichwere lacking in the susceptible cultivars Extra thickening inpencyclic cells as a response to the entrance of haustonum wasobserved in cultivars N-13 and IS-4202 Ten cultivars studied showed differential haustorial reactionsThese reactions included extra thickening in the pericycle inresponse to haustonal infestation, haustonal collapse, tylosts-likeocclusions in the xylem vessels, and the deposition of dark-stainingmaterials in the cortex Although no definite conclusion couldbe drawn regarding the relationship between the degree of mechanicaltissue development and field resistance, there was evidencethat some field-resistant cultivars have strong mechanical tissuesThere could, however, be other factors governing resistanceto Striga in the field Striga asiatica, sorghum, haustorium, anatomy, endodermis, pot test, host resistance mechanism, parasitization, susceptibility     

Thiophene Content in Normal and Transformed Root Cultures of Tagetes erecta: A Comparison with Thiophene Content in Roots of Intact Plants

Transformed roots of Tagetes erecta were obtained followinginfection of stems of sterile plantlets with Agrobacterium rhizogenesstrain TR105. The thiophenes detected were 5-(4-hydroxy-l-butenyl)-2,2'-bithienyl,5-(4-acetoxy-l-butenyl)-2,2'-bithienyl, 5-(3-buten-l-enyl)-2,2',-bithienyl and 2.2': 5', 2'-terthienyl. The thiophene patternwas the same in normal root cultures and roots of the intactplant. Transformed roots showed a higher growth rate and a higherbiomass yield than normal root cultures on a hormone-free media. Key words: Transformed roots normal roots, Tagetes erecta, thiophenes, Agrobacterium rhizogenes     

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.     

Radial Hydraulic Conductivity of Individual Root Tissues of Opuntia ficus-indica (L.) Miller as Soil Moisture Varies

The constraints on water uptake imposed by individual root tissueswere examined forOpuntia ficus-indicaunder wet, drying, andrewetted soil conditions. Root hydraulic conductivity (L_P) andaxial conductance (K_h) were measured for intact root segmentsfrom the distal region with an endodermis and from midroot witha periderm;L_Pwas then measured for each segment with successivetissues removed by dissection. Radial conductivity (L_R) wascalculated fromL_PandK_hfor the intact segment and for the individualtissues by considering the tissue conductivities in series.Under wet conditions,L_Rfor intact distal root segments was lowestfor the cortex; at midroot, where cortical cells are dead,L_Rforthe cortex was higher and no single tissue was the predominantlimiter ofL_R.L_Rfor the endodermis and the periderm were similarunder wet conditions. During 30d of soil drying,L_Rfor the distalcortex increased almost three-fold due to the death of corticalcells, whereasL_Rfor the midroot cortex was unaffected;L_Rforthe endodermis and the periderm decreased by 40 and 90%, respectively,during drying. For both root regions under wet conditions, thevascular cylinder had the highestL_R, which decreased by 50–70%during 30d of soil drying. After 3d of rewetting, new lateralroots emerged, increasingL_Rfor the tissues outside the vascularcylinder as well as increasing uptake of an apoplastic tracerinto the xylem of both the roots and the shoot. The averageL_Rforintact root segments was similar under wet and rewetted conditions,but the conductivity of the tissues outside the vascular cylinderincreased after rewetting, as did the contribution of the apoplasticpathway to water uptake. Opuntia ficus-indica; prickly pear; root hydraulic conductivity; endodermis; periderm; apoplast; lateral root emergence     

Germination of Tagetes minuta L. I. Temperature Effects

Initial studies have indicated that Tagetes minuta achenes haveboth a temperature and a light requirement for germination.Temperatures tested were 10, 20, 25, 30 and 35 °C. Germinationwas optimal at 25 °C under white light conditions. Underthese conditions 100 per cent of achenes germinated within 7days of imbibition. There was no germination at 10 or 35 °Ceither in the light or in the dark. Achenes imbibed and incubatedat 35 °C for 4 days showed no visible signs of germinationbut on transfer to 25 °C, 100 per cent of these achenesgerminated within 24 h. Furthermore, achenes given this hightemperature (35 °C) treatment could be dried at 25 °C,re-imbibed at 25 °C and again 100 per cent of achenes germinatedwithin 24 h of re-imbibition. This rapid germination responsefollowing removal from the high temperature regime could alsobe induced by transfer to temperatures of 20 °C or 20 °C(16 h) alternating with 10 °C (8 h). Tagetes minuta L., weed seeds, germination, temperature, light     

Casparian Strips in the Leaf Intrastelar Canals of Isoetes duriei Bory, a Mediterranean Terrestrial Species

Anatomical observations, using light and fluorescence microscopy,were made on leaves of Isoetes duriei to verify the presenceof casparian bands around the intrastelar canals. This peculiaranatomical feature, previously reported for some Isoetes species,is confirmed. The possible role of this endodermis-like structure,in the transport of water due to root pressure or in the accumulationof certain metabolites, is discussed in relation to the ecologicaland anatomical features of the species. Copyright 2000 Annalsof Botany Company Isoetes duriei, Lycopsida, Mediterranean, leaf anatomy, endodermis, casparian strips, fluorescence microscopy     

An X-ray Microanalysis Study of the Salt Glands and Intracellular Calcium Crystals of Tamarix

X-ray microprobe analyses of the secreted salts from glandsof 20 Tamarix aphylla (L.) Karst trees growing in alluvial soilsin the north western district of Victoria, Australia, show thatthe glands secrete a variety of elements including calcium,magnesium and sulphur. However, sodium, potassium and chloride,common ions reported to be secreted predominantly in other studies,are present in relatively low amounts in the secreted salts.Calcium, the major cationic element in the secretory productof the gland, was not detected in the symplasm of the secretoryand collecting cells or in the vacuoles of the collecting cells.Some evidence indicates that silicon may be secreted by theglands but further corroboratory data are required. Our resultssupport previous suggestions that the glands of Tamarix havea low level of selectivity. Large, spherical aggregates of calcium crystals were observedin the vacuoles of the mesophyll cells and quantitative X-raymicroanalysis suggested that the chemical composition of thecrystalline aggregates was CaSO₄, 2H₂O. The predominant elementsin the vacuolar sap were magnesium and sulphur, probably presentas MgSO₄, whereas the major elements in the cytoplasm were potassium,sulphur and phosphorus. In Tamarix aphylla the calcium contentof the leaf appears to be regulated by both the secretion ofcalcium salts from the leaf and by intracellular calcificationin mesophyll cells.Copyright 1994, 1999 Academic Press X-ray microanalysis, Tamarix, salt gland, secretion, salts, ions, calcium crystals, compartmentation     

Response of Cultured Embryos of Phaseolus vulgaris and Hordeum vulgare to Farnesol

Excised embryos of Phaseolus vulgaris incubated in a mediumcontaining 10 mg dm^–3 farnesol showed enhanced root growthwhereas the leaves remained rudimentary At lower concentrationsof exogenous farnesol normal leaf development occurred and rootgrowth was comparable to untreated cultures. Enhanced root growthalso occurred when excised embryos of Hordeum vulgare were treatedwith farnesol but only at 10 mg dm^–3 and this treatmentdid not prevent leaf growth X-ray micro-probe analysis of leavesrevealed an increased phosphorus content in P vulgaris and adecreased sulphur content in H vulgare in comparison to untreatedplants. Hordeum vulgare L., barley, Phaseolus vulgaris, bean, embryo culture, farnesol, X-ray microprobe analysis, root growth     

Structural Associations Between Mitochondria and Chloroplasts in the Bundle Sheath Cells of Portulaca oleracea

Mitochondria and chloroplasts are structurally associated inthe bundle sheath cells of Portulaca oleracea L., an NAD malicenzyme type C₄ plant. These associations occur in some restrictedregions where the mitochondrial cristae extend inwards. Exposureof plants to 1.0 µ11^–1 SO₂ for 3 h induced shrinkageof mitochondria of the bundle sheath cells, which further visualizedthe structural association between the organelles. C₄ plant, chloroplast, mitochondrion, Portulaca oleracea, sulphur dioxide