Chlorella triggers stomatal closure mediated by NADPH oxidase and improves instantaneous water use efficiency in Vicia faba

Integrating microalgae growth in biomethane plants: Process design, modelling, and cost evaluation

The integration of microalgae cultivation in anaerobic digestion (AD) plants can take advantage of relevant nutrients (ammonium and ortho-phosphate) and CO2 loads. The proposed scheme of microalgae integration in existing biogas plants aims at producing approximately 250 t·y-1 of microalgal biomass, targeting the biostimulants market that is currently under rapid expansion. A full-scale biorefinery was designed to treat 50 kt·y-1 of raw liquid digestate from AD and 0.45 kt·y-1 of CO2 from biogas upgrading, and 0.40 kt·y-1 of sugar-rich solid by-products from a local confectionery industry. An innovative three-stage cultivation process was designed, modelled, and verified, including: i) microalgae inoculation in tubular PBRs to select the desired algal strains, ii) microalgae cultivation in raceway ponds under greenhouses, and iii) heterotrophic microalgae cultivation in fermenters. A detailed economic assessment of the proposed biorefinery allowed to compute a biomass production cost of 2.8 ± 0.3 €·kg DW-1, that is compatible with current downstream process costs to produce biostimulants, suggesting that the proposed nutrient recovery route is feasible from the technical and economic perspective. Based on the case study analysis, a discussion of process, bioproducts and policy barriers that currently hinder the development of microalgae-based biorefineries is presented.

PLDα1 and GPA1 are involved in the stomatal closure induced by Oridonin in Arabidopsis thaliana

Oridonin is an important diterpenoid, which plays an important role in plant growth and development. PLDα1 and GPA1 are involved in many biotic or abiotic stresses. In this study, using the seedlings of Arabidopsis thaliana L. wild type (WT), PLDα1 defective mutant (pldα1), GPA1 defective mutant (gpa1) and pldα1/gpa1 double mutant as materials, the effect of stomatal apertures responding to Oridonin and the functions of PLDα1 and GPA1 in this response were investigated. The results showed that 60 μmol·L-1 of Oridonin induced stomatal closure and significantly increased the relative expression levels of GPA1 and PLDα1. Oridonin increased H2O2 accumulation in guard cells by inhibiting the antioxidant enzymes. The increase of H2O2 caused the expression of OST1, which is a positive regulatory gene for stomatal closure. Both PLDα1 and GPA1 were involved in Oridonin-induced stomatal closure and PLDα1 acted downstream of GPA1. The results suggested that Oridonin caused stomatal closure by affecting GPA1 and promoting PLDα1 to produce PA, and further accumulating H2O2 to upregulate gene OST1.

Algae biostimulants: A critical look at microalgal biostimulants for sustainable agricultural practices

For the growing human population to be sustained during present climatic changes, enhanced quality and quantity of crops are essential to enable food security worldwide. The current consensus is that we need to make a transition from a petroleum-based to a bio-based economy via the development of a sustainable circular economy and biorefinery approaches. Both macroalgae (seaweeds) and microalgae have been long considered a rich source of plant biostimulants with an attractive business opportunity in agronomy and agro-industries. To date, macroalgae biostimulants have been well explored. In contrast, microalgal biostimulants whilst known to have positive effects on development, growth and yields of crops, their commercial implementation is constrained by lack of research and cost of production. The present review highlights the current knowledge on potential biostimulatory compounds, key sources and their quantitative information from algae. Specifically, we provide an overview on the prospects of microalgal biostimulants to advance crop production and quality. Key aspects such as specific biostimulant effects caused by extracts of microalgae, feasibility and potential of co-cultures and later co-application with other biostimulants/biofertilizers are highlighted. An overview of the current knowledge, recent advances and achievements on extraction techniques, application type, application timing, current market and regulatory aspects are also discussed. Moreover, aspects involved in circular economy and biorefinery approaches are also covered, such as: integration of waste resources and implementation of high-throughput phenotyping and -omics tools in isolating novel strains, exploring synergistic interactions and illustrating the underlying mode of microalgal biostimulant action. Overall, this review highlights the current and future potential of microalgal biostimulants, algal biochemical components behind these traits and finally bottlenecks and prospects involved in the successful commercialisation of microalgal biostimulants for sustainable agricultural practices.