Comparison between discarded facemask and common plastic waste on microbial colonization and physiochemical properties during aging in seawater.

Facemasks are indispensable for preventing the spread of COVID-19. However, improper disposal of discarded facemasks has led to their contamination in the marine environment. To understand the environmental risk of this emerging plastic pollution, it's important to clarify the features that distinguish discarded facemasks from common plastic waste during aging. This study compared the microbial colonization, degradation-related enzymes, and physicochemical properties among surgical masks, polystyrene cups, polycarbonate bottles, and polyethylene terephthalate bottles in their aging processes in natural seawater. Compared to the other plastic wastes, surgical masks were colonized by the most diverse microorganisms, reaching 1521 unique prokaryotic OTUs after 21-day exposure in seawater. Moreover, the activity of eukaryotic enzymes associated with plastic degradation was 80-fold higher than that in seawater, indicating that the colonized eukaryotes would be the major microorganisms degrading the surgical masks. Meanwhile, the nano-sized defects (depth between 8 and 61 nm) would evolve into cracks of bigger sizes and result in the breakage of the microfibers and releasing microplastics into the ocean. Overall, our study demonstrated a distinctive plastisphere occurred in surgical masks from both microbial and physiochemical aspects. This work provides new insights for assessing the potential risk of plastic pollution caused by the COVID-19 pandemic.

Organosilicon and inorganic silica inhibit polystyrene nanoparticles uptake in rice.

Nanoplastics (NPs) have become an emerging global environmental problem, and the toxicity of polystyrene nanoplastics (PS-NPs) in rice plants has received widespread attention. However, few studies have focused on silicon (Si)-mediated interactions between PS-NPs and rice. Thus, two forms of Si (organosilicon/inorganic silica) treated rice cells were exposure of positively or negatively charged NPs, PS-NH2 and PS-COOH, to evaluate the effects of Si for defense against PS-NPs toxicity in rice. The result showed PS-NH2 nanoparticles were accumulated at relatively low levels in cells compared with that of PS-COOH, but induced a higher accumulation of hydrogen peroxide (H2O2) and superoxide radicals (O2•-). However, both organosilicon and inorganic silica can generate more negative potential on the surfaces of cell wall to absorb large numbers of positively charged PS-NH2. In addition, they can prevent the uptake of both PS-NH2 and PS-COOH through reducing the porosity on the surface of the cell walls. These finally alleviated the toxicity of oxidative stress caused by PS-NPs and improved the viability of rice cells. Our findings demonstrated the significant contribution of Si in combating PS-NPs in rice.

The Xyloglucan Endotransglucosylase/Hydrolase Gene XTH22/TCH4 Regulates Plant Growth by Disrupting the Cell Wall Homeostasis in Arabidopsis under Boron Deficiency.

TCH4 is a xyloglucan endotransglucosylase/hydrolase (XTH) family member. Extensive studies have shown that XTHs are very important in cell wall homeostasis for plant growth and development. Boron (B), as an essential micronutrient for plants, plays an essential role in the cross-linking of cell wall pectin. However, the effect of B on cell wall organization is unclear. This study aimed to explore the mechanism of plant adaption to B stress by investigating the role of TCH4 in cell wall homeostasis. We conducted both plate and hydroponic cultures of wild-type Col-0 and overexpression and gene knockout lines of XTH22/TCH4 to analyze the phenotype, components, and characteristics of the cell wall using immunofluorescence, atomic force microscopy (AFM), and transmission electron microscopy (TEM). B deficiency induces the expression of TCH4. The overexpression lines of TCH4 presented more sensitivity to B deficiency than the wild-type Col-0, while the knockout lines of TCH4 were more resistant to low B stress. Up-regulation of TCH4 influenced the ratio of chelator-soluble pectin to alkali-soluble pectin and decreased the degree of methylesterification of pectin under B-deficient conditions. Moreover, we found that B deficiency disturbed the arrangement of cellulose, enlarged the gap between cellulose microfibrils, and decreased the mechanical strength of the cell wall, leading to the formation of a thickened and deformed triangular region of the cell wall. These symptoms were more profound in the TCH4 overexpression lines. Consistently, compared with Col-0, the O2- and MDA contents in the TCH4 overexpression lines increased under B-deficient conditions. This study identified the B-deficiency-induced TCH4 gene, which regulates cell wall homeostasis to influence plant growth under B-deficient conditions.

Organically-bound silicon enhances resistance to enzymatic degradation and nanomechanical properties of rice plant cell walls.

Plant cell walls exhibit excellent mechanical properties, which form the structural basis for sustainable bioresources and multifunctional nanocelluloses. The wall nanomechanical properties of living cells through covalent modifications of hybrid inorganic elements, such as silicon, may confer significant influence on local mechano-response and enzymatic degradation. Here, we present a combination of ex situ measurements of enzyme-released oligosaccharide fragments using MALDI-TOF MS and in situ atomic force microscopy (AFM) imaging through PeakForce quantitative nanomechanical mapping of tip-functionalized single-molecule enzyme-polysaccharide substrate recognition and the nanoscale dissolution kinetics of individual cellulose microfibrils of living rice (Oryza sativa) cells following silicate cross-linking of cell wall xyloglucan. We find that xyloglucan-bound silicon enhances the resistance to degradation by cellulase and improves the wall nanomechanical properties in the elastic modulus at the single-cell level. The findings establish a direct link between an inorganic element of silicon and the nanoscale architecture of plant cell wall materials for sustainable utilization.

Cell wall-bound silicon optimizes ammonium uptake and metabolism in rice cells.

Background and Aims: Turgor-driven plant cell growth depends on cell wall structure and mechanics. Strengthening of cell walls on the basis of an association and interaction with silicon (Si) could lead to improved nutrient uptake and optimized growth and metabolism in rice (Oryza sativa). However, the structural basis and physiological mechanisms of nutrient uptake and metabolism optimization under Si assistance remain obscure. Methods: Single-cell level biophysical measurements, including in situ non-invasive micro-testing (NMT) of NH4+ ion fluxes, atomic force microscopy (AFM) of cell walls, and electrolyte leakage and membrane potential, as well as whole-cell proteomics using isobaric tags for relative and absolute quantification (iTRAQ), were performed. Key Results: The altered cell wall structure increases the uptake rate of the main nutrient NH4+ in Si-accumulating cells, whereas the rate is only half in Si-deprived counterparts. Conclusions: Rigid cell walls enhanced by a wall-bound form of Si as the structural basis stabilize cell membranes. This, in turn, optimizes nutrient uptake of the cells in the same growth phase without any requirement for up-regulation of transmembrane ammonium transporters. Optimization of cellular nutrient acquisition strategies can substantially improve performance in terms of growth, metabolism and stress resistance.