Radial gas diffusion from roots of rice (Oryza sativa L.) and Kallar grass (Leptochloa fusca L. Kunth), and effects of inoculation withAzospirillum brasilense Cd

Cortical root air space (aerenchyma) helps rice and Kallar grass to survive flooding conditions. The dependence of the oxygen concentration in the rhizosphere on the root aerenchyma volume, the plant age,-species and plant respiration is described. Additionally diffusional effects of different types of gases are evaluated. Inoculation of the rhizosphere with the micro-aerobically N₂-fixing microorganismAzospirillum brasilense Cd brought about an increased oxygen concentration in the rhizosphere by the factor 3.3 for rice and 5.3 for Kallar grass. This effect is thought to be due to enhanced root cell wall permeability probably caused by IAA-like phytohormones released by the bacteria.     

Close Association of Azospirillum and Diazotrophic Rods with Different Root Zones of Kallar Grass

The populations of diazotrophic and nondiazotrophic bacteria were estimated in the endorhizosphere and on the rhizoplane of Kallar grass (Leptochloa fusca) and in nonrhizosphere soil. Microaerophilic diazotrophs were counted by the most-probable-number method, using two semisolid malate media, one of them adapted to the saline-sodic Kallar grass soil. Plate counts of aerobic heterotrophic bacteria were done on nutrient agar. The dominating N₂-fixing bacteria were differentiated by morphological, serological, and physiological criteria. Isolates, which could not be assigned to a known species, were shown to fix nitrogen unequivocally by ¹⁵N₂ incorporation. On the rhizoplane we found 2.0 × 10⁷ diazotrophs per g (dry weight) of root, which consisted in equal numbers of Azospirillum lipoferum and Azospirillum-like bacteria showing characteristics different from those of known Azospirillum species. Surface sterilization by NaOCI treatment effectively reduced the rhizoplane population, so that bacteria released by homogenization of roots could be regarded as endorhizosphere bacteria. Azospirillum spp. were not detected in the endorhizosphere, but diazotrophic, motile, straight rods producing a yellow pigment occurred with 7.3 × 10⁷ cells per g (dry weight) of root in the root interior. In nonrhizosphere soil we found 3.1 × 10⁴ nitrogen-fixing bacteria per g. Diazotrophs were preferentially enriched in the Kallar grass rhizosphere. In nonrhizosphere soil they made up 0.2% of the total aerobic heterotrophic microflora, on the rhizoplane they made up 7.1%, and in the endorhizosphere they made up 85%. Owing to high numbers in and on roots and their preferential enrichment, we concluded that diazotrophs are in close association with Kallar grass. They formed entirely different populations on the rhizoplane and in the endorhizosphere.     

Solid state fermentation of straw withNeurospora crassa for CMCase and β-glucosidase production

Summary CMCase and -glucosidase were produced by the mutantNeurospora crassa 40b cultivated on untreated wheat straw in a solid state fermentation. Best enzyme activities were observed when the growth medium was composed of wheat straw mixed with certain mineral solutions at a ratio 1:2 (w/v). A partially purified enzyme preparation showed optimum enzyme activities of CMCase and -glucosidase at pH 4.0 and 5.0 and temperature 50 and 60°C respectively. The apparent Km values for the same enzymes were 16.8 g/l and 1.03x10^–4 M respectively. At optimum growth and enzyme assay conditions yields as high as 586.2 U CMCase and 58.4 U -glucosidase per gram of straw were obtained.     

Phytoremediative potential of salt-tolerant grass species for cadmium and lead under contaminated nutrient solution

Abstract

Phytoremediation of heavy metal contaminated soils represents a promising technique and salt-tolerant hyperaccumulators for multiple metals are the need of time. Therefore, phytoremediation potential of four salt-tolerant grass species [Dhab (Desmostachya bipinnata), Kallar (Leptochloa fusca), Para (Brachiaria mutica) and Sporobolus (Sporobolus arabicus Boiss)] was evaluated for cadmium (Cd) and lead (Pb) in a hydroponic study. The plants were harvested after a growth period of 3 months in a nutrient solution containing different levels of Cd (0, 5, and 25?mg?L^?1) and Pb (0, 25, and 125?mg L^?1). Results indicated that Dhab grass showed the highest root and shoot dry matter yield followed by Para, Kallar and Sporobolus grass irrespective of metal or its level under which they were grown. All the grass species showed considerable Cd-accumulating potential with an accumulation of >150?mg kg^?1of shoot dry matter at a higher level of Cd-contamination (25?mg?L^?1). While in case of shoot Pb-accumulation only Para grass performed well and accumulated Pb >1000?mg kg^?1 of shoot dry matter at the higher level of Pb-contamination (125?mg?L^?1). Moreover, Para and Dhab grasses performed better for shoot Cd-uptake, while only Para grass showed promising shoot Pb uptake potential. In conclusion, these grass species could be penitentially used for phytoremediation of salt-affected Cd and Pb contaminated soils.     

Solid state fermentation and fractionation of oat straw by Basidiomycetes

Summary Seventee white-rot and brown-rot fungi were screened for their ability to fractionate the lignocellulose structure of oat straw through the preferential attack of lignin or cellulose. Fermentations were carried out under solid-state conditions with 25 g quantities of straw. The fermented straw was analyzed for weight loss, Klason lignin loss and cellulase digestion. All the fungi attacked both lignin and carbohydrate fractions causing 3–28% weight losses and 26–34 g/100 g enzymatic digestibility. Polyporus tulipiferae, Phanerochaete chrysosporium and Polyporus sp. were tested for the effects of various nitrogen, phosphate and carbon levels, incubation temperatures and incubation time. The three fungi had different responses to these factors.     

Cross-Reaction of Predominant Nitrogen-Fixing Bacteria with Enveloped, Round Bodies in the Root Interior of Kallar Grass

Diazotrophic rods occurring in high numbers (about 10⁸ rods per g [dry weight] of root) in the root interior of Kallar grass were localized by indirect immunofluorescence in cross sections of the same roots. Specifically stained round bodies which were apparently covered by a nonantigenic envelope were found in the aerenchymatic tissue.     

Root-Zone-Specific Oxygen Tolerance of Azospirillum spp. and Diazotrophic Rods Closely Associated with Kallar Grass

The effect of oxygen on N₂-dependent growth of two Azospirillum strains and two diazotrophic rods closely associated with roots of Kallar grass (Leptochloa fusca) was studied. To enable precise comparison, bacteria were grown in dissolved-oxygen-controlled batch and continuous cultures. Steady states were obtained from about 1 to 30 μM O₂, some of them being carbon limited. All strains needed a minimum amount of oxygen for N₂-dependent growth. Nitrogen contents between 10 and 13% of cell dry weight were observed. The response of steady-state cultures to increasing O₂ concentrations suggested that carbon limitation shifted to internal nitrogen limitation when N₂ fixation became so low that the bacteria could no longer meet their requirements for fixed nitrogen. For Azospirillum lipoferum Rp5, increase of the dilution rate resulted in decreased N₂ fixation in steady-state cultures with internal nitrogen limitation. Oxygen tolerance was found to be strain specific in A. lipoferum with strain Sp59b as a reference organism. Oxygen tolerance of strains from Kallar grass was found to be root zone specific. A. halopraeferens Au 4 and A. lipoferum Rp5, predominating on the rhizoplane of Kallar grass, and strains H6a2 and BH72, predominating in the endorhizosphere, differed in their oxygen tolerance profiles. Strains H6a2 and BH72 still grew and fixed nitrogen in steady-state cultures at O₂ concentrations exceeding those which absolutely inhibited nitrogen fixation of both Azospirillum strains. It is proposed that root-zone-specific oxygen tolerance reflects an adaptation of the isolates to the microenvironments provided by the host plant.     

Influence of oxygen and carbon dioxide on lignin degradation in solid state fermentation of wheat straw withStropharia rugosoannulata

Summary In solid state fermentation,Stropharia rugosoannulata degrades lignin of wheat straw slightly better in the presence of oxygen than that in air. The sub-atmospheric partial pressure of oxygen (0.05 atm.) inhibits lignin and organic matter degradation. the increasing partial pressure of carbon dioxide (0.1–0.3 atm.) along with 0.2 atm. of oxygen does not have any effect on lignin degradation, but slightly decreases organic matter loss and increases thein vitro digestibility of fermented wheat straw, thereby making the process more efficient.     

Production of xylanases byChaetomium cellulolyticum during growth on lignocelluloses

Summary Chaetomium cellulolyticum was able to produce xylanases on all the three lignocelluloses: wheat straw, corn stover and aspen wood. Wheat straw was the best. Solid state fermentation of lignocelluloses gave higher yields of xylanases than liquid state fermentation, but it took longer time of incubation.     

Comparative water-use efficiency of Sporobolus arabicus and Leptochloa fusca and its relation with carbon-isotope discrimination under semi-arid conditions

Water-use efficiency (WUE) of Leptochloa fusca (L.) Kunth (Kallar grass) and Sporobolus arabicus Boiss. was determined under different soil moisture regimes. Plants grown in lysimeters were subjected to three soil moisture regimes, viz. well-watered (100%), medium-watered (75%), and low-watered (50%) of total available water (TAW). The soil moisture was restored on alternate days by adding the required volume of water on the basis of neutron moisture meter readings taken from neutron access tubes installed in each lysimeter. The grasses were harvested after suitable intervals (4 months) to obtain maximum biomass. Leaf samples collected at each harvest were analyzed for carbon-isotope discrimination (¹³C) with an isotope ratio (¹³C/¹²C) mass spectrometer. Results indicated significant differences in WUE of both grasses subjected to different water regimes. Sporobolus arabicus showed higher WUE than Kallar grass. However, Kallar grass showed better value of yield response factor (k _y = 0.649) compared with Sporobolus (k _y = 1.06) over the entire season. The data confirm that these grasses can be grown successfully in water-limited environments by selecting an optimum soil moisture level for maximum biomass production. The mean carbon-isotope discrimination (¹³C) of Kallar grass (–14.4) and Sporobolus (–12.8) confirm that both are C₄ plants. The carbon-isotope discrimination () was significantly and negatively correlated with WUE of the two species studied. The results of the present study confirm that ¹³C or of leaves can be used as good predictor of WUE in some C₄ plants.     

Improvement of degraded physical properties of a saline-sodic soil by reclamation with kallar grass (Leptochloa fusca)

A field experiment was conducted to evaluate the effectiveness of growing salt tolerant plants to improve the physical characteristics of a saline-sodic soil. Kallar grass [Leptochloa fusca (L.) Kunth], a species tolerant to salinity, sodicity and alkalinity, was irrigated for five years with poor quality ground water (EC = 0.14 S m^–1, SAR_adj=19.3, RSC = 9.7 meq L^–1). The soil physical properties of plant available water, saturated hydraulic conductivity, structural stability, bulk density and porosity were determined at the end of each year. The growth of kallar grass for three years significantly improved the physical properties of the soil and these were maintained with further growth of grass up to five years. Kallar grass significantly increased plant available water with time (r=0.97^**). The available water was highly correlated (r=0.92^**) with increases in soil organic matter content, porosity (r=0.99^**) and other physical properties. Soil hydraulic conductivity increased substantially with time from 0.035 to 55.6 mm d^–1 in the topsoil (0–20 cm) in five years and was significantly correlated with porosity, water retention, structural stability and organic matter content of soil. The soil structural stability index improved significantly from 32 to 151 with kallar grass and showed greater increases in the surface soil than at depth. The cropping of kallar grass resulted in a linear increase of soil organic matter content (r=0.92^**) which improved porosity and other soil physical properties (r0.82^*). This study confirmed that kallar grass is effective for rehabilitation and restoration of soil fertility in saline-sodic areas on a sustainable basis.     

Growth and enzyme production by Polyporus hirsutus in presence of ammonium sulphate

Summary Growth of Polyporus hirsutus on rice straw rapidly increases its susceptibility to cellulase and xylanase. Addition of ammonium sulphate to the straw (0.1 g/g) enhances cellulase and xylanase production but does not affect laccase production by the fungus although it appears to inhibit its growth.     

小麦秸秆水浸提液对五种植物化感作用的研究

该文研究了不同浓度的小麦秸秆水浸提液对徐州地区2种玉米(郑单958和农大108)和3种常见玉米田间杂草(马唐、稗草和反枝苋)种子萌发和幼苗生长的影响。结果表明:当小麦秸秆浸提液浓度分别大于75、50和25 g·L~-1时,马唐、稗草和反枝苋种子的萌发受到显著的抑制;当小麦秸秆浸提液浓度分别大于50和37.5 g·L~-1时,玉米郑单958和农大108种子的萌发受到显著的抑制;但当小麦秸秆浸提液浓度大于37.5 g·L~-1时,马唐、稗草和反枝苋幼苗根和芽的生长均受到明显的抑制;当小麦秸秆浸提液浓度小于75 g·L~-1时,玉米郑单958和农大108幼苗根与芽的生长受到明显的促进,且郑单958幼苗叶片中叶绿素的含量以及郑单958的POD酶活性均得到提高。该研究结果表明较高浓度的小麦秸秆浸提液(50 g·L~-1)会抑制杂草的生长,有利于玉米郑单958的生长,为小麦秸秆还田和玉米田杂草的生态防治提供了理论基础。     

Evidence for a plasmid conferring salt-tolerance in the plant-root associated,diazotrophKlebsiella sp. NIAB-I

Summary Using analytical and preparative methods, we demonstrated the presence of an indigenous plasmid (pNIAB-I) in a diazotroph,Klebsiella sp. NIAB-I isolated, from the roots of Kallar grass, growing on saline lands in Pakistan. The plasmid is approximately 50 kilobase (kb) in size. Transformation experiments indicated that non-halophilic bacteria such asE. coli K12 strain (MV10) andK. pneumoniae M5AI on acquiring this plasmid become tolerant to high salt (NaCl) and alkaline pH.     

Plant-bacteria interactions with special emphasis on the kallar grass association

Kallar grass is a highly salt-tolerant grass grown as a pioneer plant on alkaline, salt-affected soils in Pakistan. Nitrogen-fixing bacteria and kallar grass were found to be in close association, which was even root-zone specific: rhizoplane and endorhizosphere were colonized by two different populations. Among theAzospirillum isolates originating from the root surface, some were of a new species, now namedA. halopraeferens. To study plant-bacterium interactions, this natural kallar grass association was chosen. The possible role of bacterial chemotaxis and oxygen tolerance are discussed.     

Thermostable tryptophan synthase ofBacillus stearothermophilus expressed inEscherichia coli

Summary The tryptophan synthase genes,trpA andtrpB, from a moderate thermophile,Bacillus stearothermophilus IFO13737, were expressed efficiently inEscherichia coli. The recombinant tryptophan synthase amounted to 22% of the soluble cellular protein, and was purified to homogeneity by three steps. The enzyme is more thermostable thanE.coli tryptophan synthase, especially the subunit. The enzyme is also more resistant to sodium dodecylsulfate and methanol thanE.coli enzyme.     

Presence of two subunit types in ribulose-1,5-bisphosphate carboxylase from blue-green algae.

Ribulose-1,5-bisphosphate car?ylase (E.C. 4.1.1.39) from 2 blue-green algae, Plectonema boryanum and Anabaena variabilis, was isolated by sucrose density gradient centrifugation. Both enzymes had a sedimentation value of about 18s, similar to that of Chromatium enzyme. The presence of two subunits (A, B) in the algal enzyme was demonstrated by Nadodecyl sulfate polyacrylamide gel electrophoresis. The molecular weight of the two subunits was determined: for Plectonema A, 5.4 × 10⁴ and B, 1.3 × 10⁴ and Anabaena A, 5.2 × 10⁴ and B, 1.3 × 10⁴, respectively. The car?ylase reaction catalysed by the algal enzyme was similar to the higher plant enzyme in exhibiting the Mg²⁺-effect, the optimal pH shifting from alkaline to neutral by elevating the concentration of Mg²⁺ in the assay mixture. The rabbit antisera developed against the spinach ribulose-1,5-bisphosphate car?ylase and its catalytic oligomer exhibited significant inhibitory effects on the car?ylation reaction catalysed by the algal enzyme.     

Kinetics of rice straw methane fermentation

Summary The kinetics of anaerobic fermentation of rice straw to methane were studied. Rice straw was the only carbon source at influent volatile solid concentrations of 18.9 and 37.8 g/l. Semicontinous runs were carried out at 37°C in laboratory scale perfectly mixed reactors. The Contois' kinetic model constants were calculated from the experimental data. Arefrac tory coefficient was measured (R=0.374) to account for the nonbiodegradable portion of the organic matter of rice straw and incorporated into the kinetic equations. The predicted values of effluent substrate concentration, volumetric methane yield, volumetric methane production rate, and biodegradable conversion efficiency fit well with those measured experi mentally.Percent destruction values of feed constituents were measured.     

Determination of cellobiohydrolase from culture filtrate ofTrichoderma viride by the method of single immunodiffusion and enzyme linked immunosorbent assay

Summary Immunological methods (single immunodiffusion and enzyme linked immunosorbent assay) to determine the specific level of cellobiohydrolase in the culture filtrate ofTrichoderma viride showed good agreement with enzyme assay on filter paper.     

Solid state fermentation of oat straw by Polyporus sp A-336 and the effect of added sugars

Summary Supplementing oat straw in SSF by Polyporus sp A-336 with xylose, mannose, glucose and arabinogalactan at levels of 5 and 10% of straw weight stimulated lignin degradation and cellulose hydrolysis. Degradation of lignin, hemicellulose and cellulose was monitored for 30 days in plain straw, and straw plus xylose and showed that xylose shortened the lag in lignin breakdown and slowed hemicellulose utilization. At 24 days, similar polymer losses occurred in both systems and enzymatic cellulose hydrolysis had reached a maximum of 47% weight loss.