Silicification of bamboo (Phyllostachys heterocycla Mitf.) root and leaf

Bamboo is a silicon accumulating plant. In leaves, the major place of silicon (Si) deposition is the epidermis, with the highest concentration of Si in silica cells. In bamboo roots, the deposition of Si is found only in endodermal cell walls. The silicification of leaves and roots was examined in the economically important bamboo plant Phyllostachys heterocycla, using an environmental scanning electron microscope coupled with X-ray microanalysis, as well as gravimetric quantification. The content of Si on a dry weight basis measured by gravimetric quantification was 7.6% in leaves and 2.4% in roots, respectively. Moreover, quantification of EDX data showed high Si impregnation of the inner tangential endodermal walls. Si content in this part of the root endodermal cell walls was even higher than that in the outer leaf epidermal walls, where conspicuous deposition of Si often occurs in grass plants.     

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-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.     

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     

Growth and Gas Exchange of Three Sorghum Cultivars Under Drought Stress

A field study was conducted to evaluate the drought tolerance of three sorghum [Sorghum bicolor (L.) Moench] cultivars, Gadambalia, Arous elRimal and Tabat, and quantify the physiological bases for differences in their drought tolerance. Water stress reduced shoot dry mass of Gadambalia, Arous elRimal and Tabat by 43, 46 and 58 %, respectively. The respective reduction in leaf area of the three cultivars was 28, 54 and 63 %. The reduction in net photosynthetic rate, stomatal conductance and transpiration rate due to water stress was lowest in Gadambalia and highest in Tabat. The leaf water potentials and relative water contents of Gadambalia under wet and dry treatments were similar, while those of Tabat were significantly reduced by water stress. The lowest and highest liquid water flow conductance was displayed by Tabat and Gadambalia, respectively. Drought tolerance in Gadambalia is associated with its smaller leaf area, higher liquid water flow conductance, and ability to maintain high leaf water potential, relative water content, stomatal conductance, transpiration rate and photosynthetic rate under drought stress. This revised version was published online in July 2006 with corrections to the Cover Date.     

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     

Expression analysis of a stress-modulated transcript in drought tolerant and susceptible cultivars of sorghum (Sorghum bicolor)

The present study reports the cloning of a 581 bp sequence, designated as SbEST8, from the osmotically stressed germinated seeds of a drought tolerant cultivar of sorghum (Sorghum bicolor). The SbEST8, which shows no homology with the reported gene sequences, is present in multiple copies and lacks restriction fragment length polymorphism among different sorghum cultivars. The expression of SbEST8 in the germinating seeds of sorghum was modulated by different abiotic stresses. Kinetic studies revealed that imposition of osmotic stress after 8h resulted in maximum levels of SbEST8 mRNA in the germinating seeds of cv. ICSV-272, with further stress causing a decline to undetectable levels by 16 h. However, relieving the stress after 12h resulted in an enhancement of SbEST8 mRNA levels for at least another 4h following which it declined. The decrease in SbEST8 mRNA levels in the leaves at 30 DAS in response to drought stress was observed only in the drought susceptible cultivar (CSV-216), whereas its expression was either increased substantially or remained unaffected in the tolerant cultivars, thus suggesting its role in water stress tolerance.     

Application of silicon enhanced drought tolerance in Sorghum bicolor

The effects of silicon application on the drought tolerance of sorghum ( Sorghum bicolor (L.) Moench) were investigated for two cultivars differing in drought susceptibility. Silicon application ameliorated the decrease in dry weight under drought stress conditions, but had no effect on dry matter production under wet conditions. Under dry conditions, silicon-applied sorghum had a lower shoot to root (S/R) ratio, indicating the facilitation of root growth and the maintenance of the photosynthetic rate and stomatal conductance at a higher level compared with plants grown without silicon application. The diurnal determination of the transpiration rate indicated that the silicon-applied sorghum could extract a larger amount of water from drier soil and maintain a higher stomatal conductance. Very similar effects of silicon application were observed for both cultivars regardless of their drought susceptibility. These results suggest that silicon application may be useful to improve the drought tolerance of sorghum via the enhancement of water uptake ability.     

Subcellular localization of mineral deposits in the roots of wheat (Triticum aestivum L.)

Summary Mineral distribution in the roots of wheat (Triticum aestivum L. cv. Wheaton) was investigated using X-ray microanalysis of bulk frozen hydrated roots in SEM and of freeze substituted sections in TEM. Results obtained using the two methods agreed reasonably well. A total often elements were detected: Na, Mg, Si, P, S, Cl, K, Ca, Mn, and Fe. Of these Si, P, Ca, and Mn were incorporated into biomineralized structures. Silica was deposited in the endodermal walls in the older parts of the root. Silicon was also detected in the large central metaxylem lumina in the basal zone of the root, and in the smaller peripheral metaxylem and the immediately contiguous pericycle and outer parenchyma cells bridging the small metaxylem vessels to the endodermal layer. In the basal zone of the root some of the inner cortical cells contained intracellular electron opaque deposits. These were associated with the cell walls, had non-opaque inclusions and microanalysis revealed that they consisted of calcium, phosphorus and manganese.Abbreviations A apical zone of root - M midzone of root - B basal zone of root - SEM scanning electron microscope - TEM transmission electron microscope     

干旱胁迫下小麦幼苗根、叶多胺含量和多胺氧化酶活性的变化

 以抗旱性不同的两个小麦品种（‘晋麦33’和‘温麦8’）（Triticum aestivum cv. Jinmai 33 and Wenmai 8）为材料,研究了干旱胁迫下多胺含量和多胺氧化酶活性的变化。结果表明：旱过程中,幼苗根、叶中腐胺（Put）、亚精胺（Spd）、精胺（Spm）3种多胺含量和多胺氧化酶（PAO）活性先迅速升高,而后下降。与抗旱性弱的‘晋麦33’相比,抗旱性强的品种‘温麦8’幼苗根、叶中Spd、Spm 含量初期升高幅度大,之后下降速率减慢;PAO活性的变化与之相反,‘晋麦33’的PAO活性提高的幅度大于‘温麦8号’。多胺含量和PAO活性在小麦幼苗的根与叶之间呈极显著正相关。干旱初期,小麦根、叶中多胺迅速积累可能是干旱胁迫反应的一个信号,随后较高的Spd、Spm 水平有利于增强小麦幼苗的抗旱性。     

Changes in water relation parameters under osmotic and salt stresses in maize and sorghum

A relatively drought tolerant cultivar of maize ( Zea mays L. cv. Pioneer 3950) and a drought tolerant line of sorghum ( Sorghum bicolor [L.] Moench cv. ICSV 112) were grown hydroponically for 11 days. Treatments for non-ionic osmotic and salt stresses were started at the 8th day by addition of polyethylene glycol 6000 and NaCl, respectively, at 200 mOsm equivalent concentrations in the presence or absence of 0. 1 μ M abscisic acid. Relative growth rate was depressed by both stress factors, more severely for maize than sorghum. Abscisic acid increased the growth rate and reverted the negative effect of NaCl in maize, while sorghum was only slightly affected. In general, sorghum had higher levels of K⁺ and lower levels of Na⁺ and the K⁺/Na⁺ ratio was further increased by abscisic acid treatment. From the pressure-volume curves, osmotic potential, the water potential at turgor loss point, bulk elastic modulus and the water saturation deficit at initial turgor loss were estimated. Most significantly, sorghum had a higher elastic modulus than maize and it decreased under osmotic treatment, while in maize it increased under NaCl stress. The results suggest that bulk tissue turgor was not limiting growth under these conditions and underscores the possible implications of changes in the elastic condition of the cell walls in stress responses.     

Augmenting drought tolerance in sorghum by silicon nutrition

Silicon (Si) distribution and accumulation in plant organs is widely reported as beneficial to overcome biotic and abiotic stresses. The investigation on distribution of Si in plant organs under water stress conditions was studied through experiments conducted at Arid Agriculture University, Pakistan during 2007–2009. Treatments (Si₂₀₀: 200 ml l^?1 of potassium silicate and Si₀: control or absence of silicon) were replicated thrice with two sorghum cultivars; SPV462 (drought susceptible) and Johar-1 (drought tolerant) screened using osmotic media of PEG-6000 (?4.0, ?6.0, ?8.0 and ?10.0 MPa). The results exhibited increased leaf water potential, leaf area index, SPAD chlorophyll with increased silicon concentration in leaves and roots of drought-tolerant genotype as compared to SPV462. Johar-1 exhibited maximum values for net assimilation and relative growth rate under silicon treatment in comparison to silicon absence. Similarly, maintenance of transpiration rate, because of accumulation of silicon in leaves resulted in optimum leaf water potential and optimum growth of crop.     

Growth,abscisic acid content,and carbon isotope composition in wheat cultivars grown under different soil moisture

Changes in dry matter accumulation and allocation, abscisic acid content and carbon isotope composition of three wheat cultivars from dry, middle and wet climate regions were recorded at full maturity after exposure to different watering regimes (100, 50 and 25 % field capacity). Compared with the wet climate cultivar, the dry climate cultivar showed lower stem height, total leaf area, total dry biomass and total grain dry mass, and higher root/shoot ratio, abscisic acid content and carbon isotope composition under all watering regimes. Both water-limited treatments significantly reduced leaf growth and increased dry matter allocation into the roots leading to a significant raise of root/shoot ratio in all cultivars tested. In addition, drought affected morphological and physiological properties more in the dry climate cultivar than in the wet climate cultivar.     

干旱胁迫对小麦幼苗根系生长和叶片光合作用的影响

采用水培试验方法,以2个耐旱性不同的小麦品种(敏感型望水白和耐旱型洛旱7号)为材料,研究了干旱胁迫对小麦幼苗根系形态、生理特性以及叶片光合作用的影响,以期揭示小麦幼苗对干旱胁迫的适应机制.结果表明： 干旱胁迫下,2个小麦品种幼苗的根系活力显著增大,而根数和根系表面积受到抑制;干旱胁迫降低了望水白的叶片相对含水量,提高了束缚水/自由水,而对洛旱7号无显著影响;干旱胁迫降低了2个小麦品种叶片的叶绿素含量、净光合速率、蒸腾速率、气孔导度和胞间CO2浓度,但随胁迫时间的延长,洛旱7号的叶绿素含量和净光合速率与对照差异不显著;干旱胁迫降低了2个小麦品种幼苗的单株叶面积,以及望水白的根系、地上部和植株生物量,而对洛旱7号无显著影响.水分胁迫下,耐旱型品种可以通过提高根系活力、保持较高的根系生长量来补偿根系吸收面积的下降,保持较高的根系吸水能力,进而维持较高的光合面积和光合速率,缓解干旱对生长的抑制.     

不同耐盐品种棉花根系主要指标对盐分胁迫的响应

以盐敏感品种‘中棉所45’(CCRI45)、弱耐盐品种‘新陆早17号’(XLZ17)、中等耐盐品种‘新陆早13号’(XLZ13)和耐盐品种‘中棉所35’(CCRI35)为试验材料,利用根系分析系统研究盐分胁迫下棉花根系形态特征及其与棉株耐盐性的关系.结果表明:盐分胁迫显著降低棉花根和叶的干质量以及K^+/Na^+,其中耐盐品种CCRI35和中等耐盐品种XLZ13的根干质量、叶干质量以及根中K^+/Na^+分别比盐敏感品种CCRI45提高了69.3%~104.4%、24.8%~45.3%和25.0%~45.8%;盐分胁迫显著抑制棉花根系生长发育,其中CCRI 35和XLZ13的总根长、根系总表面积、根系总体积以及0~10 cm土层中直径为0~1.2 mm内的根长、根表面积和根体积均显著高于CCRI45,分别增加了15.2%~85.8%、12.0%~68.5%、31.7%~217.8%、27.2%~73.9%、39.6%~74.3%和99.0%~309.7%.主成分分析表明,比根长、浅层根长比例和细根比例受基因型差异的影响较为明显,是区分不同耐盐品种棉花根系形态差异的主要指标.逐步回归分析显示,比根长、0~10 cm土层的粗根根长、细根根表面积、粗根根表面积、粗根体积、中根比例,以及10~20 cm粗根根长、粗根表面积、粗根体积等根系参数对盐分响应敏感.耐盐棉花品种可通过维持表层根长比例、细根比例和比根长的增加来适应盐分胁迫.     

Oxidative stress, protein carbonylation, proteolysis and antioxidative defense system as a model for depicting water deficit tolerance in Indica rice seedlings

Water deficit is an important constraint to rice (Oryza sativa L.) productivity. The present study was undertaken to investigate whether the level of oxidative stress, carbonylation of proteins, proteolysis and status of antioxidative defense could serve as a model to distinguish water deficit tolerant and sensitive rice cultivars. When 10-day-grown seedlings of two rice cultivars, Malviya-36 (drought-sensitive) and Brown Gora (drought-tolerant) were subjected to ?1.0 and ?2.1 MPa water deficit treatments for 24–72 h with polyethylene glycol 6000 in the medium, a greater decline in the growth of the seedlings and levels of leaf water potential, relative water content, Chl a, Chl b, carotenoids and greater increase in leaf water loss were observed in the sensitive cultivar than the tolerant. Under similar level of water deficit seedlings of sensitive cultivar showed higher level of superoxide anion generation, H₂O₂, lipid peroxidation and proteolysis in roots as well as shoots compared to the tolerant. Drought-tolerant cultivar had higher constitutive level of antioxidative enzymes superoxide dismutase and catalase and the activities of these two enzymes alongwith of guaiacol peroxidase showed greater increase in this cultivar under water deficit compared to the sensitive. A significant decline in the level of protein thiol and a higher increase in protein carbonyls content, also confirmed by protein gel blot analysis with an antibody against 2,4-dinitrophenylhydrazine was observed in the seedlings of drought sensitive cv. Malviya-36 compared to the tolerant cv. Brown Gora when subjected to similar level of water deficit. Seedlings of drought sensitive cultivar, under water deficit, showed higher proteolytic activity, higher number of in-gel activity stained proteolytic bands and higher expression of oxidized proteins in roots compared to the tolerant cultivar. Results suggest that poor capacity of antioxidative enzymes could be, at least partly, correlated with water deficit sensitivity of sensitive cultivar and that higher activity of antioxidative enzymes superoxide dismutase, catalase, guaiacol peroxidase, low proteolytic activity, lower level of protein carbonyls and protein thiolation could serve as a model to depict water deficit tolerance in Indica rice seedlings.     

Development of the Hypodermal Casparian Band in Corn and Onion Roots

A hypodermal Casparian band develops 40–50 mm from theroot tip in corn and 30–40 mm from the root tip in onion.In both plants, the endodermal Casparian band matures about20 mm closer to the root tip than the hypodermal Casparian band.Using the apoplastic fluorescent dye, Calcofluor white M2R (CFW),a permeability barrier could be distinguished in the radialwalls of the hypodermis 40–50 mm from the root tip incorn and onion. In progressively younger regions of the roots,CFW was first excluded from the outer tangential hypodermalwalls and the inner tangential epidermal walls, then the radialepidermal walls so that in very young regions only the outertangential epidermal walls were permeated. In contrast to CFW,the symplastic fluorescent dye, uranin, was translocated fromthe epidermis into the stele at all distances tested (5.0–50mm from the root tips). CFW and uranin at a concentration of0.01% proved nontoxic to corn and onion roots on the basis ofroot growth tests. Key words: Zea mays, Casparian band, Hypodermis, Allium cepa     

Effect of Water Stress on Photosynthesis in Two Mulberry Genotypes with Different drought Tolerance

Three-month-old mulberry (Morus alba L.) cultivars (drought tolerant S13 and drought sensitive S54) were subjected to water stress for 15 d. Water stress decreased the leaf water potential, net photosynthetic rate (PN), and stomatal conductance (gs) in both the cultivars. However, the magnitude of decline was comparatively greater in the sensitive cultivar (S54). Intercellular CO2 concentration (Ci) was unaltered during mild stress, but significantly increased at severe stress in both cultivars. The photosystem 2 activity significantly declined only at a severe stress in both cultivars. The Ci/gs ratio representing the mesophyll efficiency was greater in the tolerant cultivar S13. Involvement of stomatal and/or non-stomatal components in declining PN depended on the severity and duration of stress. However, the degree of non-stomatal limitations was relatively less in the drought tolerant cultivar.     

Electron-probe Microanalysis of Silicon in the Roots of Oryza sativa L.

Employing the electron-probe microanalyser, the localizationof silicon in the different tissues of the mature root of ricehas been investigated. Deposition of silicon is specific tothe endodermis. The heaviest accumulation is associated withthe inner tangential walls and to some extent the radial wallsof the endodermal cells.