Chlorella pyrenoidosa as a potential bioremediator: Its tolerance and molecular responses to cadmium and lead.

Heavy metal contamination negatively affects plants and animals in water as well as soils. Some microalgae can remove heavy metal contaminants from wastewater. The aim of this study was to screen green microalgae (GM) to identify those that tolerate high concentrations of toxic heavy metals in water as possible candidates for phytoremediation. Analyses of the tolerance, physiological parameters, ultrastructure, and transcriptomes of GM under Cd/Pb treatments were conducted. Compared with the other GM, Chlorella pyrenoidosa showed stronger tolerance to high concentrations of Cd/Pb. The reduced glutathione content and peroxidase activity were higher in C. pyrenoidosa than those in the other GM. Ultrastructural observations showed that, compared with other GM, C. pyrenoidosa had less damage to the cell surface and interior under Cd/Pb toxicity. Transcriptome analyses indicated that the "peroxisome" and "sulfur metabolism" pathways were enriched with differentially expressed genes under Cd/Pb treatments, and that CpSAT, CpSBP, CpKAT2, Cp2HPCL, CpACOX, CpACOX2, and CpACOX4, all of which encode antioxidant enzymes, were up-regulated under Cd/Pb treatments. These results show that C. pyrenoidosa has potential applications in the remediation of polluted water, and indicate that antioxidant enzymes contribute to Cd/Pb detoxification. These findings will be useful for producing algal strains for the purpose of bioremediation in water contamination.

Fabricating High-Thermal-Conductivity, High-Strength, and High-Toughness Polylactic Acid-Based Blend Composites via Constructing Multioriented Microstructures.

The massive accumulation of plastic waste has caused a serious negative impact on the human living environment. Replacing traditional petroleum-based polymers with biobased and biodegradable poly(l-lactic acid) (PLLA) is considered an effective way to solve this problem. However, it is still a great challenge to manufacture PLLA-based composites with high thermal conductivity and excellent mechanical properties via tailoring the microstructures of the blend composites. In the present work, a melt extrusion-stretching method is utilized to fabricate biodegradable PLLA/poly(butylene adipate-co-butylene terephthalate)/carbon nanofiber (PLLA/PBAT/CNF) blend composites. It is found that the incorporation of the extensional flow field induces the formation of multioriented microstructures in the composites, including the oriented PLLA molecular chains, elongated PBAT dispersed phase, and oriented CNFs, which synergistically improve the thermal conductivity and mechanical properties of the blend composites. At a CNF content of 10 wt %, the in-plane thermal conductivity, tensile strength, and elongation at break of the blend composite reach 1.53 Wm-1 K-1, 66.8 MPa, and 56.5%, respectively, which increased by 31.9, 73.5, and 874.1% compared with those of the conventionally hot-compressed sample (1.16 Wm-1 K-1, 38.5 MPa, and 5.8%, respectively). The main mechanism for the improved thermal conductivity is that the multioriented structure promotes the formation of a CNF thermal conductive network in the composites. The strengthening mechanism is attributed to the orientation of both PLLA molecular chains and CNFs in the stretching direction, restricting the movement of PLLA molecular segments around CNFs, and the toughening mechanism is due to the transformation of PLLA molecular chains from low-energy gt conformers to high-energy gg conformers induced by extensional flow field. More interestingly, after the extrusion-stretched samples are annealed, the oriented PLLA molecular chains form oriented crystal structures such as extended-chain lamellae, common "Shish-kebabs," and hybrid Shish-kebabs, which further enhance the thermal conductivity and heat resistance of the samples. This work reveals the effects of the orientation of the matrix molecular chains and crystallites on the thermal conductivity and mechanical properties of composites and provides a new way to prepare high-performance PLLA-based composites with high thermal conductivity, excellent mechanical properties, and high heat resistance.

Molecular Characterization of a Tolerant Saline-Alkali Chlorella Phosphatidate Phosphatase That Confers NaCl and Sorbitol Tolerance.

The gene encoding a putative phosphatidate phosphatase (PAP) from tolerant saline-alkali (TSA) Chlorella, ChPAP, was identified from a yeast cDNA library constructed from TSA Chlorella after a NaCl treatment. ChPAP expressed in yeast enhanced its tolerance to NaCl and sorbitol. The ChPAP protein from a GFP-tagged construct localized to the plasma membrane and the lumen of vacuoles. The relative transcript levels of ChPAP in Chlorella cells were strongly induced by NaCl and sorbitol as assessed by northern blot analyses. Thus, ChPAP may play important roles in promoting Na-ion movement into the cell and maintaining the cytoplasmic ion balance. In addition, ChPAP may catalyze diacylglycerol pyrophosphate to phosphatidate in vacuoles.

Freely switchable super-hydrophobicity and super-hydrophilicity of sponge-like poly(vinylidene fluoride) porous fibers for highly efficient oil/water separation.

Highly efficient oil/water separation ability is a prerequisite for the actual application of the membranes in oily sewage treatment, which is closely related to the surface feature and the porous structure of the membranes. In this work, the electrospun poly(vinylidene fluoride) (PVDF) porous fibers were firstly fabricated through blend-electrospinning with poly(vinyl pyrrolidone) (PVP) and then treating in distilled water. The results showed that the fibers exhibited the sponge-like porous structure, and a few PVP was reserved in the fibers due to the relatively good interaction between PVDF and PVP. The fibrous membrane exhibited high porosity, super-wettability with freely switchable super-lipophilicity and super-hydrophilicity. The oil adsorption capacities as well as the oil and water fluxes were measured, and the oil adsorption capacities were varied in the range of 22.7-76.0 g/g, and oil and water fluxes were 54,737.3 and 56,869.9 L/(m2h), respectively. Specifically, the PVDF porous fibrous membranes showed excellent separation abilities and they could highly efficiently separate oil from oil-in-water emulsions or separate water from water-in-oil emulsions, accompanied with the extremely high water or oil flux. This work confirms that the PVDF membranes composed of the porous fibers can be used in wastewater treatment.

Physiological Responses and Yield of Wheat Plants in Zinc-Mediated Alleviation of Drought Stress.

To evaluate the physiological responses of wheat to zinc (Zn) fertilizer application under drought stress, pot, and field experiments were conducted on wheat plants grown under different soil moistures and treated with soil and foliar Zn applications. Photosynthetic characteristics, antioxidant content, Zn element concentration, and the transcription level of genes involved in antioxidant biosynthesis were analyzed. Zn application increased SPAD and Fv/Fm of wheat flag leaves, while decreased lipid peroxidation levels and H2O2 content. Zn application increased the antioxidant content (ascorbate, reduced glutathione, total phenolic, and total flavonoid) of wheat flag leaves, and enhanced the relative expression levels of two antioxidant enzyme genes, four ascorbate-glutathione cycle genes, and two flavonoid biosynthesis pathway genes under drought stress. Soil Zn application increased grain yield and Zn concentration by 10.5 and 15.8%, 22.6 and 9.7%, and 28.2 and 32.8% under adequate water supply, moderate drought, and severe drought, respectively. Furthermore, foliar application of Zn in the field increased grain yield and grain Zn concentration under both adequate water supply and rain-fed conditions. Zn plays a role in alleviating wheat plant drought stress by Zn-mediated increase in photosynthesis pigment and active oxygen scavenging substances, and reduction in lipid peroxidation. Furthermore, Zn fertilizer could regulate multiple antioxidant defense systems at the transcriptional level in response to drought.

Effect of nitrogen fertilisation and irrigation on phenolic content, phenolic acid composition, and antioxidant activity of winter wheat grain.

BACKGROUND: Understanding the variance of antioxidant in wheat grain responses to irrigation and nitrogen (N) fertiliser management will improve the nutrient quality of wheat grain. Four N rates (0, 180, 240, and 300 kg ha(-1)) combined with irrigation times (I0, no irrigation; I1, jointing time irrigation; I2, jointing + flowering time irrigation), were used to determine the effect of N fertilisation and irrigation on total phenolic content (TPC), phenolic acid composition, and antioxidant activity (AOA) of wheat grain. RESULTS: Irrigation, N fertilisation and their interactions had significant effect on TPC, total flavonoid content (TFC), AOA, p-coumaric acid (PCA), as well as vanillic acid (VA) and chlorogenic acid (CA). I1 N300 treatment had the highest TPC at Zhengzhou and Wenxian (1451.5 µg g(-1) and 1397.9 µg g(-1), respectively) location, while I1 N240 resulted in the highest TFC (0.75 mg g(-1)) and VA (19.77 µg g(-1)) at Wenxian. TPC, TFC, AOA, ferulic acid (FA), PCA and VA increased with N application rate (from 180 to 300 kg N ha(-1)). CONCLUSION: An appropriate irrigation and N management improved antioxidant content and AOA in wheat grain. Generally, I1 N240 and I1 N300 treatment resulted in the higher TPC, TFC, AOA, as well as phenolic acid, i.e. FA and VA.

Expression of flavonoid biosynthesis genes and accumulation of flavonoid in wheat leaves in response to drought stress.

Flavonoids are the low molecular weight polyphenolic secondary metabolic compounds, and have various functions in growth, development, reproduction, and stress defense. However, little is known about the roles of the key enzymes in the flavonoids biosynthesis pathway in response to drought stress in winter wheat. Here, we investigated the expression pattern of flavonoids biosynthesis genes and accumulation of flavonoids in wheat leaves under drought stress. Quantitative real-time PCR analysis showed that there were a rapid increase in expression levels of TaCHS, TaCHI, TaF3H, TaFNS, TaFLS, TaDFR, and TaANS under drought stress in two wheat cultivars Aikang 58 (AK) and Chinese Spring (CS). The cultivar CS exhibited higher genes expression levels of TaCHS, TaCHI, TaF3H, TaFLS, TaDFR, and TaANS, and the cultivar AK showed a higher expression level of TaFNS gene during drought treatment. The increase rates of genes expression were superior in AK compared to CS. Total phenolics content, total flavonoids content, anthocyanin content, and schaftoside content in wheat leaves were enhanced during drought treatment and cultivar CS had a relative higher accumulation. These results suggest that the flavonoids pathway genes expression and accumulation of flavonoids compounds may be closely related to drought tolerant in wheat. Further, flavonoids response mechanism may be different between wheat cultivars.