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.     

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.     

Leaf Abscission Zones in Molinia caerulea (L.) Moench, the Purple Moor Grass

Leaf separation and loss in the grass Molinia caerulea (L.)Moench was investigated using scanning electron microscopy.Leaf senescence and subsequent shedding of leaves was precededby the formation of a leaf abscission zone. The zone containscells which have more than doubled their wall thickness to greaterthan 0-4 µm. The line of fracture associated with thezone principally followed the middle lamellae, leaving intactcells on the fracture faces. Molinia should prove an interestingmodel in which to study abscission processes in the Gramineae. Molinia caerulea, leaf abscission zone, electron microscopy     

Effect of Nutrition on the Short-term Response of Molinia caerulea to Defoliation

Overwintering, rooted basal internodes of Molinia caerulea (L.)Moench were taken from the field and subjected to four nutritiontreatments [an adequate (high) and suboptimal (low) level ofnitrogen (N) x an adequate (high) and suboptimal (low) levelof phosphorus (P)] and three degrees of defoliation (12 treatmentsin total). Growth parameters were studied using both non-destructivemeasurements and destructive harvesting. High N supply and highP supply increased both the number of tillers and mass of eachtiller. Interactions between the effects of N and P did occurfor several growth variables; in general this was due to anabsence of a response to P supply at low N. Defoliation reducedthe dry weight of basal internodes and roots produced and temporarilyreduced leaf dry weight per tiller. There were no effects ofdefoliation on tillering. Interactions of defoliation with bothN supply and P supply were observed. Leaf extension rate wasincreased by defoliation at low, but not high N, and the adverseeffects of defoliation on root dry weight and root/shoot (R/S)ratios were proportionally greater at low N. The results arediscussed in relation to other investigations which have reportedcontrasting aspects of Molinia growth in response to both nutrientsand defoliation. Molinia caerulea, purple moor grass, nitrogen, phosphorus, defoliation     

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     

Variation in Molinia caerulea (L.) Moench, the Purple Moor Grass, in Relation to Edaphic Environments

Two diverse population of Molinia caerulea (L.) Moench, onegrowing on a Ca²⁺-rich, alkaline, Leblanc waste tip, the otheron an acid moorland, were investigated. It was anticipated thata comparative study of the morphology, growth and floweringpatterns, protein composition, specific isoenzyme and root-surfacephosphatase activities of both populations would clarify thetaxonomic status of populations of Molinia and help towardsunderstanding the ability of M. caerulea to colonize widelydiffering habitats. Both populations were identified as Moliniacaerulea caerulea. The Molinia growing on Leblanc spoil displayedcharacteristics typified by r-selected plants, i.e. displayinglarger flowers after faster development. Acid moorland plantsshowed greater vegetative development and were more typicalof K-selected types. These differences between the more vigorousshoot growth of the moorland compared to the waste tip plantspersisted under controlled conditions, irrespective of the mediain which they were grown. Root surface phosphatase activityshowed a plastic response to edaphic pH which may contributeto the success of M. caerulea caerulea in colonizing diversehabitats.Copyright 1995, 1999 Academic Press Molinia, edaphic extremes, variation, morphometry, enzyme activities, plasticity, colonization, taxonomy     

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 Effects of Nitrogen Supply and Defoliation on the Seasonal Internal Cycling of Nitrogen in Molinia caerulea

Plants of Molinia caerulea were grown in pots for two seasonsat two levels of nitrogen (N) supply and two levels of defoliation.All N supplied was enriched with ¹⁵N in the first season andwas at natural abundance in the second season. This allowedthe contribution of remobilization from overwintering storesto be discriminated from current root uptake in supplying Nfor new shoot growth in the second season. The effects of Nsupply and defoliation upon the internal cycling of N in M.caerulea were quantified. N was remobilized from both roots and basal internodes to supportnew shoot, especially leaf, growth in spring. Roots suppliedmore N than basal internodes. Since the remobilization mainlyoccurred before the onset of root N uptake, internal cyclingwas important for the earliest period of shoot growth. An increasedN supply increased the amount of N remobilized to new shootgrowth, however, the proportion of N remobilized from overwinteringstores was independent of N supply. Defoliation increased theamount of N remobilized from the roots, and had no effect onthe ¹⁵N content of basal internodes of plants receiving a lowsupply of N. Remobilization of N from leaves of undefoliatedplants occurred later in the season. Remobilization from leavessupplied flowers in plants receiving a low N supply and bothflowers and new basal internodes in plants receiving a higherN supply. Key words: Molinia caerulea, internal cycling, nitrogen, defoliation     

The Ultrastructure and Electron-probe Microassay of Silicon Deposits in the Endodermis of the Seminal Roots of Sorghum bicolor (L.) Moench

Si deposits in the endodermis of the seminal root of Sorghumbicolor (L.) Moench., following culture in nutrient solutioncontaining 100 ppm SiO₂ for 7 days, were investigated by transmissionelectron microscopy. Si microassay was carried out by meansof the EMMA-4 system. Endodermal ultrastructure is discussed. EM micrographs of theSi deposits reveal information regarding their formative processesand indicate a considerable involvement with the cellulosicstructure of the inner tangential wall (ITW). The initial depositsare believed to be composed structurally of particles designatedas primary spherical units. The EMMA-4 conclusively indicated that Si was localized andconfined to the ITW, and the implications of this result forprevious studies are considered. Current evidence from studies of endodermal function, as wellas root translocation physiology, is utilized in arriving attentative mechanisms for silicic acid transport and subsequentSi deposition on the ITW.     

The Effect of Wind on Provenances of Molinia caerulea L.

The response of seven Welsh provenances of Molinia caeruleato wind was assessed by measuring leaf growth and tillering.Leaf growth was usually depressed whilst tillering tended toincrease. On the basis of the results, an example of a wind-resistantand wind-susceptible provenance was chosen for further study.The wind susceptible provenance displayed the lowest water potentialsin the wind treatment, but this did not arise as a result ofit having a more easily damaged leaf surface than the resistantprovenance. The essential difference between the two provenancesappears to be in the hydraulic pathway from the soil to theleaf surface. Molinia caerulea L., provenance, wind, hydraulic pathway     

The use of diachronic spatial approaches and predictive modelling to study the vegetation dynamics of a managed heathland

According to the EU Habitats Directive, heathlands are a semi-natural habitat type of community interest. This status aims at conserving these habitats, especially where and when they are threatened by various changes, including natural vegetation succession. We present results of a study of the dynamics of a typical dry heathland plot located in the Fontainebleau massif (France). An exhaustive observation of vegetation changes were made on this area of four hectares between 2000 and 2008, employing a spatial approach. We recorded the expansion of Molinia caerulea (L.) Moench at the expense of Ericaceae. The potential future vegetation of the site was modelled using Markov chains coupled to a GIS programme. This model predicted a gradual change in the floristic composition of heathland in favour of M. caerulea at the expense of Calluna vulgaris (L.) Hull and Erica tetralix L., and the expansion of Pinus sylvestris L. The study demonstrates how spatial methods can contribute to the design of reliable management methods of habitats such as the heathlands.     

Endodermal Silicification in Mature, Nodal Roots of Sorghum bicolor (L.) Moench.

Nodal roots of mature, soil-grown specimens of Sorghum bicolor(L.) Moench. were investigated for their Si content by meansof the electron-probe microanalyser and the scanning electronmicroscope. No consistent accumulation of Si occurred other than in theendodermis. Indication of a lower Si content in the old as comparedto the younger nodal roots was obtained. The solid silica depositsoccurred as domeshaped silica aggregates confined to the innertangential wall. Comparisons with the similar deposits of youngseminal roots are made. It is argued that the endodermal deposits represent a specializedaspect of silicification and contrasting hypotheses to accountfor it are proposed, one involving physico-chemical factors,the other, protoplasmic control.     

Relationships Between Nitrogen and Water Concentration in Shoot Tissue ofMolinia caeruleaDuring Shoot Development

Plants ofMolinia caeruleawere supplied with either a low (0.2mol m^-3) or high (10 mol m^-3) supply of nitrogen over two growingseasons. A total of 14 destructive plant harvests were made:when plants were in an over-wintering state prior to the secondseason; immediately following bud burst; and on 12 further occasionsthroughout the second season. The relationships between shootnitrogen concentration on a dry mass basis, shoot water contentand plant developmental stage were investigated. Shoot nitrogenconcentration on a dry mass basis fell as the growing seasonprogressed. In contrast, the concentration of nitrogen in tissuewater after bud burst showed only a slight reduction. The concentrationof nitrogen both on a dry mass basis and in tissue water wasgreater for plants receiving the higher supply of nitrogen.Shoot water content was highest immediately following bud burstthen declined as the season progressed, with plants receivingthe low nitrogen supply having slightly greater shoot watercontents. It was concluded that the decline in shoot nitrogenconcentration ofM. caeruleaon a dry mass basis as the mass increasedwas mainly explained by changes in shoot water content. Theobserved increase in the rate of decline of both shoot nitrogenconcentration and water content with increased shoot mass coincidedwith the cessation of leaf tissue production and was thereforedue to a switch from the production of leaves to other tissues.Copyright1999 Annals of Botany Company Molinia caerulea(L.), purple moor grass, nitrogen, water content, shoot development.     

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     

A laboratory assessment of the relative susceptibility of Molinia caerulea (L.) Moench and Calluna vulgaris (L.) Hull to a range of herbicides

There is a concern that Molinia caerulea (L.) Moench may be increasing in upland moorland communities at the expense of Calluna vulgaris (L.) Hull and other ericaceous species. In order to develop a strategy for the control of Molinia, laboratory studies were carried out to determine the dose-response relationships of seven graminicides and glyphosate on both Molinia caerulea and Calluna vulgaris. Plants were grown under laboratory conditions and sprayed with increasing doses of herbicide using a precision sprayer. Results were highly variable, indicating the great morphological plasticity of these two species, making determination of the ED₅₀ difficult. Glyphosate, quizalofop-ethyl and sethoxydim successfully reduced various measures of Molinia growth to 50% of control levels (ED₅₀ estimates ranged from 0.41–0.67 kg a.i. ha^-1, 0.18–1.20 kg a.i. ha^-1and 0.37–0.49 kg a.i. ha^-1respectively). In contrast, only glyphosate reduced Calluna growth significantly (ED₅₀s ranged from 0.025–0.45 kg a.i. ha^-1), whilst selective herbicides left it undamaged. A comparison of the results for Molinia and Calluna suggests that there is no application rate of glyphosate which will reduce Molinia effectively whilst leaving Calluna undamaged. Recommendations for field testing of selective herbicides are discussed.     

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     

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     

Investigation of P and S Distributions in the Roots of Tagetes patula L. using Micro-PIXE

A proton microprobe for energy-dispersive PIXE-analysis hasbeen used to measure elemental distributions of sulphur andother elements in roots of Tagetes patula L. by making a line-scanalong the diameter of the cross-section. Higher concentrationsof phosphorus and sulphur were found in or near the phloem.In addition the endodermis contained an increased sulphur concentration.The results obtained and future possibilities for this kindof investigation are discussed. Key words: Tagetes patula L., micro-PIXE, sulphur, thiophenes, endodermis, Pratylenchus penctrans (Cobb)     

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     

Internal Nitrogen Dynamics in the Graminoid Molinia caerulea Under Higher N Supply and Elevated CO2 Concentrations

Nutrient resorption from senescing leaves is an important aspect of internal plant nutrient cycling. Global environmental change very likely affects this process. In an 8-month experiment, we investigated the effect of increased nitrogen (N) availability and CO₂ concentration on the contribution of leaf N resorption to the internal nitrogen dynamics of the perennial deciduous graminoid Molinia caerulea (L.) Moench. Plants were grown in a factorial combination of two levels of N (65 and 265 N ha⁻¹ year⁻¹) and CO₂ (380 and 700 μL L⁻¹) in a greenhouse. Both N and CO₂ addition increased the total biomass and the total N pools of mature Molinia plants considerably, without a significant interaction. Nitrogen-resorption efficiency from senescing leaves (% of the mature leaf N pool that is resorbed) was neither affected by the N- nor by the CO₂ treatments. When averaged over the treatments, the N-resorption efficiency was 85% ± 1 (SE). The final N concentration in the litter (N-resorption proficiency) was also not affected by the treatments and was on average 3.6 mg N g⁻¹ ± 0.25 (SE). The contribution of resorbed N from senescing leaves to the late seasonal N requirements (seed and stem production and storage of N for next year’s growth) of M. caerulea plants was (negatively) affected by the N treatment only, and no interaction effects with CO₂ were found. Resorption from stems and/or direct reserve and seed formation during growth became relatively more important. Thus, internal N cycling processes in Molinia caerulea are only affected when N availability is increased, but not under elevated CO₂ concentrations. Under high N conditions, this species shifts from a N recycling strategy to reserve formation during growth.