Bioimaging structural signatures of the oomycete pathogen Sclerospora graminicola in pearl millet using different microscopic techniques.

In this case study, the mycelium growth of Sclerospora graminicola in the infected tissues of pearl millet and the process of sporulation and liberation of sporangia and zoospores were observed using four different microscopic techniques. The cotton blue-stained samples observed under light microscope revealed the formation of zoospores with germ tubes, appressoria and initiation of haustorium into the host cells, while the environmental scanning electron microscopy showed the rapid emergence of sporangiophores with dispersed sporangia around the stomata. For fluorescence microscopy, the infected leaf samples were stained with Fluorescent Brightener 28 and Calcofluor White, which react with ß-glucans present in the mycelial walls, sporangiophores and sporangia. Calcoflour White was found to be the most suitable for studying the structural morphology of the pathogen. Therefore, samples observed by confocal laser scanning microscopy (CLSM) were pre-treated with Calcofluor White, as well as with Syto-13 that can stain the cell nuclei. Among the four microscopic techniques, CLSM is ideal for observing live host-pathogen interaction and studying the developmental processes of the pathogen in the host tissues. The use of different microscopic bioimaging techniques to study pathogenesis will enhance our understanding of the morphological features and development of the infectious propagules in the host.

Structural changes and enzymatic response of Napier grass (Pennisetum purpureum) stem induced by alkaline pretreatment.

Napier grass is a promising energy crop in the tropical region. Feasible alkaline pretreatment technologies, including NaOH, Ca(OH)2, NH3, and alkaline H2O2 (aH2O2), were used to delignify lignocellulose with the aim of improving glucose recovery from Napier grass stem cellulose via enzymatic saccharification. The influences of the pretreatments on structural alterations were examined using SEM, FTIR, XRD, and TGA, and the relationships between these changes and the enzymatic digestibility of cellulose were addressed. The extensive removal of lignin (84%) in NaOH-pretreated fibre agreed well with the high glucan conversion rate (94%) by enzymatic hydrolysis, while the conversion rates for fibre pretreated with Ca(OH)2, NH3, and aH2O2 approached 60%, 51%, and 42%, respectively. The substantial solubilisation of lignin created porosity, allowing increased cellulose accessibility to cellulases in NaOH-pretreated fibre. In contrast, high lignin content, lignin redeposition on the surface, and residual internal lignin and hemicellulose impeded enzymatic performance in Ca(OH)2-, NH3-, and aH2O2-pretreated fibres, respectively.

Optimization of delignification of two Pennisetum grass species by NaOH pretreatment using Taguchi and ANN statistical approach.

In the bioconversion of lignocelluloses for bioethanol, pretreatment seems to be the most important step which improves the elimination of the lignin and hemicelluloses content, exposing cellulose to further hydrolysis. The present study discusses the application of dynamic statistical techniques like the Taguchi method and artificial neural network (ANN) in the optimization of pretreatment of lignocellulosic biomasses such as Hybrid Napier grass (HNG) (Pennisetum purpureum) and Denanath grass (DG) (Pennisetum pedicellatum), using alkali sodium hydroxide. This study analysed and determined a parameter combination with a low number of experiments by using the Taguchi method in which both the substrates can be efficiently pretreated. The optimized parameters obtained from the L16 orthogonal array are soaking time (18 and 26 h), temperature (60°C and 55°C), and alkali concentration (1%) for HNG and DG, respectively. High performance liquid chromatography analysis of the optimized pretreated grass varieties confirmed the presence of glucan (47.94% and 46.50%), xylan (9.35% and 7.95%), arabinan (2.15% and 2.2%), and galactan/mannan (1.44% and 1.52%) for HNG and DG, respectively. Physicochemical characterization studies of native and alkali-pretreated grasses were carried out by scanning electron microscopy and Fourier transformation Infrared spectroscopy which revealed some morphological differences between the native and optimized pretreated samples. Model validation by ANN showed a good agreement between experimental results and the predicted responses.

Structural properties and hydrolysabilities of Chinese Pennisetum and Hybrid Pennisetum: Effect of aqueous ammonia pretreatment.

The effects of aqueous ammonia pretreatment on structural properties and hydrolysabilities of Chinese Pennisetum and Hybrid Pennisetum were investigated. Aqueous ammonia pretreatment increased cellulose crystallinities and hydrolysabilities of Chinese Pennisetum and Hybrid Pennisetum. Compared with Chinese Pennisetum, Hybrid Pennisetum showed better enzymatic digestibility. Xylanase supplementation was more effective than the increase of cellulase loadings in the hydrolysis of aqueous ammonia pretreated Chinese Pennisetum and Hybrid Pennisetum. After supplementation of 2mg of xylanase/g dry matter to 5 FPU of cellulases/g dry matter, the hydrolysis yields of cellulose of aqueous ammonia pretreated Chinese Pennisetum and Hybrid Pennisetum were 92.3-95.4%, and the hydrolysis yields of xylan were 86.9-94.2%. High hydrolysability and low dosage of enzyme loadings together with the advantages of high yield and widely distribution demonstrated the potential of Chinese Pennisetum and Hybrid Pennisetum for the production of platform sugars.

Green processing of tropical banagrass into biofuel and biobased products: an innovative biorefinery approach.

Banagrass (Pennisetum purpureum) approximately 4 months old was hand-harvested and shredded. Half of the sample was dewatered using a screw-press, whereby the extracted juice was used for cultivating an edible fungus, Rhizopus microsporus, for aquaculture feed supplementation. The remaining biomass was divided into four separate streams: (1) wet, juiced; (2) dry, juiced; (3) wet, unjuiced; and (4) dry, unjuiced. Each stream was pretreated with dilute sulfuric acid and compared on the basis of sugar release at varying acid concentrations, temperatures, and residence times. Wet, juiced banagrass released the most soluble sugars (theoretical xylose and ∼85% glucose). Ultrasonication (20 kHz) was applied to further increase monomeric sugar release but demonstrated little improvement on total sugar yields. Fungal biomass generated from banagrass juice exhibited potential as a fungal-protein production medium producing 1.16±0.34 g biomass increase/g initial biomass.

Uniparental chromosome elimination at mitosis and interphase in wheat and pearl millet crosses involves micronucleus formation, progressive heterochromatinization, and DNA fragmentation.

Complete uniparental chromosome elimination occurs in several interspecific hybrids of plants. We studied the mechanisms underlying selective elimination of the paternal chromosomes during the development of wheat (Triticum aestivum) x pearl millet (Pennisetum glaucum) hybrid embryos. All pearl millet chromosomes were eliminated in a random sequence between 6 and 23 d after pollination. Parental genomes were spatially separated within the hybrid nucleus, and pearl millet chromatin destined for elimination occupied peripheral interphase positions. Structural reorganization of the paternal chromosomes occurred, and mitotic behavior differed between the parental chromosomes. We provide evidence for a novel chromosome elimination pathway that involves the formation of nuclear extrusions during interphase in addition to postmitotically formed micronuclei. The chromatin structure of nuclei and micronuclei is different, and heterochromatinization and DNA fragmentation of micronucleated pearl millet chromatin is the final step during haploidization.