Cross-linked amylose bio-plastic: A transgenic-based compostable plastic alternative

Bio-plastics and bio-materials are composed of natural or biomass derived polymers, offering solutions to solve immediate environmental issues. Polysaccharide-based bio-plastics represent important alternatives to conventional plastic because of their intrinsic biodegradable nature. Amylose-only (AO), an engineered barley starch with 99% amylose, was tested to produce cross-linked all-natural bioplastic using normal barley starch as a control. Glycerol was used as plasticizer and citrate cross-linking was used to improve the mechanical properties of cross-linked AO starch extrudates. Extrusion converted the control starch from A-type to Vh- and B-type crystals, showing a complete melting of the starch crystals in the raw starch granules. The cross-linked AO and control starch specimens displayed an additional wide-angle diffraction reflection. Phospholipids complexed with Vh-type single helices constituted an integrated part of the AO starch specimens. Gas permeability tests of selected starch-based prototypes demonstrated properties comparable to that of commercial Mater-Bi© plastic. The cross-linked AO prototypes had composting characteristics not different from the control, indicating that the modified starch behaves the same as normal starch. The data shows the feasibility of producing all-natural bioplastic using designer starch as raw material

Community recommendations on terminology and procedures used in flooding and low oxygen stress research

Apart from playing a key role in important biochemical reactions, molecular oxygen (O2) and its by-products also have crucial signaling roles in shaping plant developmental programs and environmental responses. Even under normal conditions, sharp O2 gradients can occur within the plant when cellular O2 demand exceeds supply, especially in dense organs such as tubers, seeds and fruits. Spatial and temporal variations in O2 concentrations are important cues for plants to modulate development (van Dongen & Licausi, 2015; Considine et al., 2016). Environmental conditions can also expand the low O2 regions within the plant. For example, excessive rainfall can lead to partial or complete plant submergence resulting in O2 deficiency in the root or the entire plant (Voesenek & Bailey-Serres, 2015). Climate change-associated increases in precipitation events have made flooding a major abiotic stress threatening crop production and food sustainability. This increased flooding and associated crop losses highlight the urgency of understanding plant flooding responses and tolerance mechanisms. Timely manifestation of physiological and morphological changes triggering developmental adjustments or flooding survival strategies requires accurate sensing of O2 levels. Despite progress in understanding how plants sense and respond to changes in intracellular O2 concentrations (van Dongen & Licausi, 2015), several questions remain unanswered due to a lack of high resolution tools to accurately and noninvasively monitor (sub)cellular O2 concentrations. In the absence of such tools, it is therefore critical for researchers in the field to be aware of how experimental conditions can influence plant O2 levels, and thus on the importance of accurately reporting specific experimental details. This also requires a consensus on the definition of frequently used terms. At the 15th New Phytologist Workshop on Flooding stress (Voesenek et al., 2016), community members discussed and agreed on unified nomenclature and standard norms for low O2 and flooding stress research. This consensus on terminology and experimental guidelines is presented here. We expect that these norms will facilitate more effective interpretation, comparison and reproducibility of research in this field. We also highlight the current challenges in noninvasively monitoring and measuring O2 concentrations in plant cells, outlining the technologies currently available, their strengths and drawbacks, and their suitability for use in flooding and low O2 research

Synthetic Strigolactone GR24 Improves Arabidopsis Somatic Embryogenesis through Changes in Auxin Responses

Somatic embryogenesis in Arabidopsis encompasses an induction phase requiring auxin as the inductive signal to promote cellular dedifferentiation and formation of the embryogenic tissue, and a developmental phase favoring the maturation of the embryos. Strigolactones (SLs) have been categorized as a novel group of plant hormones based on their ability to affect physiological phenomena in plants. The study analyzed the effects of synthetic strigolactone GR24, applied during the induction phase, on auxin response and formation of somatic embryos. The expression level of two SL biosynthetic genes, MOREAXILLARY GROWTH 3 and 4 (MAX3 and MAX4), which are responsible for the conversion of carotene to carotenal, increased during the induction phase of embryogenesis. Arabidopsis mutant studies indicated that the somatic embryo number was inhibited in max3 and max4 mutants, and this effect was reversed by applications of GR24, a synthetic strigolactone, and exacerbated by TIS108, a SL biosynthetic inhibitor. The transcriptional studies revealed that the regulation of GR24 and TIS108 on somatic embryogenesis correlated with changes in expression of AUXIN RESPONSIVE FACTORs 5, 8, 10, and 16, known to be required for the production of the embryogenic tissue, as well as the expression of WUSCHEL (WUS) and Somatic Embryogenesis Receptor-like Kinase 1 (SERK1), which are markers of cell dedifferentiation and embryogenic tissue formation. Collectively, this work demonstrated the novel role of SL in enhancing the embryogenic process in Arabidopsis and its requirement for inducing the expression of genes related to auxin signaling and production of embryogenic tissue

A Comparison of Cellulose Nanocrystals and Nanofibers as Reinforcements to Amylose-Based Composite Bioplastics

Starch-based bioplastics offer a promising alternative to conventional plastics. However, they exhibit certain limitations, notably in terms of mechanical strength and barrier properties. These challenges could potentially be addressed through the incorporation of nanocellulose as a reinforcing agent. In this study, we fabricated bioplastic films using a casting and blending approach, employing highly linear pure amylose (AM) in combination with cellulose nanofibers (CNF) or cellulose nanocrystals (CNC) at various ratios. This allowed for a direct comparison of CNF and CNC functionality within the AM matrix. We systematically assessed mechanical properties and water barrier characteristics, encompassing parameters such as water permeability, moisture content, swelling, solubility, crystallinity, thermal stability, transmittance, and opacity. Additionally, we investigated water vapor and oxygen permeability. Furthermore, we delved into distinctions between CNC and CNF biocomposites. Incorporation of either type of nanocellulose yielded enhancements in film properties, with CNF exerting a more pronounced positive influence compared to CNC. Particularly noteworthy were the mechanical properties, wherein CNF composite films demonstrated markedly higher tensile strength and Young’s modulus compared to their CNC counterparts. For instance, the inclusion of 1% CNF led to a substantial increase in AM tensile strength from 66.1 MPa to 144.8 MPa. Conversely, water vapor permeability exhibited a converse behavior, as the addition of 1% CNF resulted in a significant reduction of water barrier properties from 8.7 to 1.32 g mm m−2 24 h−1kPa−1. Intriguingly, CNC films displayed greater elongation at the point of rupture in comparison to CNF films. This can be attributed to the larger surface area of the CNC and the favorable interfacial interaction between AM and CNC. Notably, the introduction of nanocellulose led to reduced film opacity and improved thermal stability. In summary, nanocellulose interacted synergistically with the AM matrix, establishing a robust hydrogen-bonded network that greatly enhanced the performance of the biocomposite films