BackgroundWheat and rice are important food crops with enormous biomass residues for biofuels. However, lignocellulosic recalcitrance becomes a crucial factor on biomass process. Plant cell walls greatly determine biomass recalcitrance, thus it is essential to identify their key factors on lignocellulose saccharification. Despite it has been reported about cell wall factors on biomass digestions, little is known in wheat and rice. In this study, we analyzed nine typical pairs of wheat and rice samples that exhibited distinct cell wall compositions, and identified three major factors of wall polymer features that affected biomass digestibility.ResultsBased on cell wall compositions, ten wheat accessions and three rice mutants were classified into three distinct groups each with three typical pairs. In terms of group I that displayed single wall polymer alternations in wheat, we found that three wall polymer levels (cellulose, hemicelluloses and lignin) each had a negative effect on biomass digestibility at similar rates under pretreatments of NaOH and H2SO4 with three concentrations. However, analysis of six pairs of wheat and rice samples in groups II and III that each exhibited a similar cell wall composition, indicated that three wall polymer levels were not the major factors on biomass saccharification. Furthermore, in-depth detection of the wall polymer features distinctive in rice mutants, demonstrated that biomass digestibility was remarkably affected either negatively by cellulose crystallinity (CrI) of raw biomass materials, or positively by both Ara substitution degree of non-KOH-extractable hemicelluloses (reverse Xyl/Ara) and p-coumaryl alcohol relative proportion of KOH-extractable lignin (H/G). Correlation analysis indicated that Ara substitution degree and H/G ratio negatively affected cellulose crystallinity for high biomass enzymatic digestion. It was also suggested to determine whether Ara and H monomer have an interlinking with cellulose chains in the future.ConclusionsUsing nine typical pairs of wheat and rice samples having distinct cell wall compositions and wide biomass saccharification, Ara substitution degree and monolignin H proportion have been revealed to be the dominant factors positively determining biomass digestibility upon various chemical pretreatments. The results demonstrated the potential of genetic modification of plant cell walls for high biomass saccharification in bioenergy crops.

Selenium (Se) is an essential trace element for humans and animals but at high concentrations, Se becomes toxic to organisms due to Se replacing sulfur in proteins. Selenium biofortification is an agricultural process that increases the accumulation of Se in crops, through plant breeding, genetic engineering, or use of Se fertilizers. Selenium phytoremediation is a green biotechnology to clean up Se-contaminated environments, primarily through phytoextraction and phytovolatilization. By integrating Se phytoremediation and biofortification technologies, Se-enriched plant materials harvested from Se phytoremediation can be used as Se-enriched green manures or other supplementary sources of Se for producing Se-biofortified agricultural products. Earlier studies primarily aimed at enhancing efficacy of phytoremediation and biofortification of Se based on natural variation in progenitor or identification of unique plant species. In this review, we discuss promising approaches to improve biofortification and phytoremediation of Se using knowledge acquired from model crops. We also explored the feasibility of applying biotechnologies such as inoculation of microbial strains for improving the efficiency of biofortification and phytoremediation of Se. The key research and practical challenges that remain in improving biofortification and phytoremediation of Se have been highlighted, and the future development and uses of Se-biofortified agricultural products in China has also been discussed.

To remove polycyclic aromatic hydrocarbons effectively, coal-based activated carbon (CAC) was produced by various microwave power modification. Original and modified CAC (MCACs) were characterized by N2 adsorption method, scanning electron microscopy, X-ray photoelectron spectroscopy, Boehm method, and point of zero charge determination. Their adsorption behavior of naphthalene was also investigated. Adsorption equilibrium isotherms, adsorption kinetics, and thermodynamics of naphthalene adsorption on CAC and MCACs were generated. Microwave modification enhanced the basic surface groups of MCACs, extended their Brunauer-Emmett-Teller surface area and pore volume, and varied their distribution of surface oxygen groups. Surface area, pore volume, and functional groups of MCACs were positively related to their naphthalene-adsorption capacity.The adsorption equilibrium of naphthalene on CAC and MCACs needed only 40 min, and this adsorption was fast. Adsorption isotherms revealed that the Freundlich model was applicable to the adsorption process. The adsorption kinetics of naphthalene onto adsorbents was described by pseudo-second-order kinetic model. Naphthalene adsorption was found to a spontaneous and exothermal adsorption process. All these results showed that microwave radiation was an efficient and rapid method of modifying activated carbons. Moreover, MCACs was a promising low-cost and fast adsorbent that can be used to remove naphthalene from aqueous solutions.

Some organic and inorganic salts could inhibit the growth of many pathogens. Selenium (Se), as an essential micronutrient, was effective in improving the plant resistance and antioxidant capacity at a low concentration. Penicillium expansum is one of the most important postharvest fungal pathogens, which can cause blue mold rot in various fruits and vegetables. In this study, the inhibitory effect of Se against P. expansum was evaluated. The result showed that Se strongly inhibited spore germination, germ tube elongation, and mycelial spread of P. expansum in the culture medium. The inhibitory effect was positively related to the concentration of Se used. Fluorescence microscopy observation of P. expansum conidia stained with propidium iodide (PI) indicated that the membrane integrity decreased to 37 % after the conidia were treated with Se (20 mg/l) for 9 h. With the use of an oxidant-sensitive probe 2,7-dichlorofluorescin (DCHF-DA), we found that Se at 15 mg/l could induce the generation of intracellular reactive oxygen species (ROS). Furthermore, methane dicarboxylic aldehyde (MDA) content, hydrogen peroxide (H2O2), and superoxide anion (O2 (-)) production rate in P. expansum spores exposed to Se increased markedly. Compared with the control, the activities of superoxide dismutase (SOD) and the content of glutathione (GSH) were reduced, confirming that damage of Se to cellular oxygen-eliminating system is the main reason. These results suggest that Se might serve as a potential alternative to synthetic fungicides for the control of the postharvest disease of fruit and vegetables caused by P. expansum.