Miscanthus has been proposed as a promising crop for phytoremediation due to its high biomass yield and remarkable adaptability to different environments. However, little is known about the resistance of Miscanthus spp. to cadmium (Cd). To determine any differences in resistance of Miscanthus to Cd, we examined plant growth, net photosynthetic rate (Pn), activities of anti-oxidant and C4 photosynthetic enzymes, concentrations of Cd in leaves and roots, and observed the chloroplast structure in three Miscanthus species treated with 0, 10, 50, 100 or 200 μM Cd in solutions. Miscanthus sinensis showed more sensitivity to Cd, including sharp decreases in growth, Pn, PEPC activity and damage to chloroplast structure, and the highest H2O2 and Cd concentrations in leaves and roots after Cd treatments. Miscanthus sacchariflorus showed higher resistance to Cd and better growth, had the highest Pn and phosphoenolpyruvate carboxylase (PEPC) activities and integrative chloroplast structure and the lowest hydrogen peroxide (H2O2) and leaf and root Cd concentrations. The results could play an important role in understanding the mechanisms of Cd tolerance in plants and in application of phytoremediation.
The molecular mechanism of low Cd influxes and accumulation in Miscanthus sacchariflorus is revealed by RNA sequencing technique. Soil cadmium (Cd) pollution has posed a serious threat to our soil quality and food security as well as to human health. Some wild plants exhibit high tolerance to heavy metals stress. However, mechanisms of Cd tolerance of wild plants remain to be fully clarified. In this study, we found that two Miscanthus species, Miscanthus (M.) sacchariflorus and M. floridulus, showed different Cd-tolerant mechanisms. M. sacchariflorus accumulated less Cd in both root and leaf by limiting Cd uptake from root and showed superior Cd tolerance, while M. floridulus not only absorbs more Cd from root but also transports more Cd to shoot. To investigate the molecular mechanism of different Cd uptake patterns in the two Miscanthus species, we analyzed the transcriptome of M. sacchariflorus and identified transcriptional changes in response to Cd in roots by high-throughput RNA-sequencing technology. A total of 92,985 unigenes were obtained from M. sacchariflorus root cDNA samples. Based on the assembled de novo transcriptome, 681 DEGs which included 345 upregulated and 336 downregulated genes were detected between two libraries of untreated and Cd-treated roots. Gene ontology (GO) and pathway enrichment analysis revealed that upregulated DEGs under Cd stress are predominately involved in metabolic pathway, starch and sucrose and biosynthesis of secondary metabolites and metal ion transporters. Quantitative RT-PCR was employed to compare the expression levels of some metal transport genes in roots of two Miscanthus species, and the genes involved in Cd uptake from root and transfer from root to shoot were extremely different. The results not only enrich genomic resource but also help to better understand the molecular mechanisms of Cd accumulation and tolerance in wild plants.
Miscanthus is a vigorous perennial Gramineae genus grown throughout the world as a promising bioenergy crop and generally regarded as heavy metal tolerant due to its ability to absorb heavy metals. However, little is known about the mechanism for heavy metal tolerance in Miscanthus. In this study, two Miscanthus species (Miscanthus sacchariflorus and Miscanthus floridulus) exhibiting different cadmium (Cd) sensitivity were used to address the mechanisms of Cd tolerance. Under the same Cd stress, M. sacchariflorus showed higher Cd tolerance with better growth and lower Cd accumulation in both shoots and roots than M. floridulus. The malate (MA) content significantly increased in root exudates of M. sacchariflorus following Cd treatment while it was almost unchanged in M. floridulus. Cellular Cd analysis and flux data showed that exogenous MA application markedly restricted Cd influx and accumulation while an anion-channel inhibitor (phenylglyoxal) effectively blocked Cd-induced MA secretion and increased Cd influx in M. sacchariflorus, indicating that MA secretion could alleviate Cd toxicity by reducing Cd uptake. The genes of malate dehydrogenases (MsMDHs) and Al-activated malate transporter 1 (MsALMT1) in M. sacchariflorus were highly upregulated under Cd stress, compared with that in M. floridulus. The results indicate that Cd-induced MA synthesis and secretion efficiently alleviate Cd toxicity by reducing Cd influx in M. sacchariflorus.
Bamboo and Miscanthus species are perennial low-input plants that are excellent candidates for bioenergy feedstock production. Biological characteristics, dry matter yields and fuel properties of the bamboo and Miscanthus have been studied. Genotype growth characteristics were determined by measurements of plant height, tillering, tuft diameter, and shoot diameter. To date, comparisons of biomass yields of bamboo and Miscanthus have not been previously reported in the literature. Bamboo and Miscanthus species were collected and previous articles describing the productivity of bamboo and Miscanthus were examined. Genotypes differed in plant height, tillering, tuft diameter, and shoot diameter. Nitrogen, temperature, water and plant density have effects on mature stands biomass production, which ranged from 5.9 to 49.5 tonnes/ha/yr for bamboo and 3.2 to 49.0 tonnes/ha/yr for Miscanthus. With such biomass yields, bamboo and Miscanthus should be considered as two very promising plants for biomass production in Zhejiang, China in the near future.
BackgroundBioflocculation has been developed as a cost-effective and environment-friendly method to harvest multiple microalgae. However, the high production cost of bioflocculants makes it difficult to scale up. In the current study, low-cost bioflocculants were produced from untreated corn stover by a biomass-degrading bacterium Pseudomonas sp. GO2.Results
Pseudomonas sp. GO2 showed excellent production ability of bioflocculants through directly hydrolyzing various biomasses. The untreated corn stover was selected as carbon source for bioflocculants’ production due to its highest flocculating efficiency compared to that when using other biomasses as carbon source. The effects of fermentation parameters on bioflocculants’ production were optimized via response surface methodology. According to the optimal model, an ideal flocculating efficiency of 99.8% was obtained with the fermentation time of 130.46 h, initial pH of 7.46, and biomass content of 0.64%. The relative importance of carboxymethyl cellulase and xylanase accounted for 51.8% in the process of bioflocculants’ production by boosted regression tree analysis, further indicating that the bioflocculants were mainly from the hydrolysates of biomass. Biochemical analysis showed that it contained 59.0% polysaccharides with uronic acid (34.2%), 32.1% protein, and 6.1% nucleic acid in the bioflocculants, which had an average molecular weight as 1.33 × 106 Da. In addition, the bioflocculants showed the highest flocculating efficiency at a concentration of 12.5 mg L−1 and were stable over broad ranges of pH and temperature. The highest flocculating efficiencies obtained for Chlorella zofingiensis and Neochloris oleoabundans were 77.9 and 88.9%, respectively.ConclusionsThe results indicated that Pseudomonas sp. GO2 can directly utilize various untreated lignocellulolytic biomasses to produce low-cost bioflocculants, which showed the high efficiency to harvest two green microalgae in a low GO2 fermentation broth/algal culture ratio.Electronic supplementary materialThe online version of this article (10.1186/s13068-017-0987-6) contains supplementary material, which is available to authorized users.
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