Meta-analysis of chitosan-mediated effects on plant defense against oxidative stress.

Chitosan, as a natural non-toxic biomaterial, has been demonstrated to enhance plant defense against oxidative stress. However, the general pattern and mechanism of how chitosan application modifies the amelioration of oxidative stress in plants have not been elucidated yet. Herein, we performed a meta-analysis of 58 published articles up to January 2022 to fill this knowledge gap, and found that chitosan application significantly increased the antioxidant enzyme activity (by 40.6 %), antioxidant metabolites content (by 24.6 %), defense enzyme activity (by 77.9 %), defense-related genes expression (by 103.2 %), phytohormones (by 26.9 %), and osmotic regulators (by 23.2 %) under stress conditions, which in turn notably reduced oxidative stress (by 32.2 %), and increased plant biomass (by 28.1 %) and yield (by 15.7 %). Moreover, chitosan-mediated effects on the amelioration of oxidative stress depended on the properties and application methods of chitosan. Our findings provide a comprehensive understanding of the mechanism of chitosan-alleviated oxidative stress, which would promote the application of chitosan in plant protection in agriculture.

Potential toxicity of nanoplastics to fish and aquatic invertebrates: Current understanding, mechanistic interpretation, and meta-analysis.

Nanoplastics (NPs) are widely detected in aquatic ecosystems and attracting considerable attention. Although ecotoxicological impacts of NPs on aquatic biota are increasingly identified, the extent and magnitude of these detrimental effects on fish and aquatic invertebrates still lack systematic quantification and mechanistic interpretation. Here, the toxicity, influencing factors, and related mechanisms of NPs to fish and aquatic invertebrates are critically reviewed and summarized based on a total of 634 biological endpoints through a meta-analysis, where five vital response categories including growth, consumption, reproduction, survival, and behavior were emphasized to elucidate the negative impacts of NPs to fish and aquatic invertebrates from physiological to molecular levels. Our results revealed that NPs significantly decreased the survival, behavior, and reproduction of fish and/or aquatic invertebrates by 56.1%, 24.2%, and 36.0%, respectively. NPs exposure increased the oxidative stress and oxidative damage by 72.0% and 9.6%, respectively; while significantly decreased antioxidant prevention system and neurotransmission by 24.4% and 15.9%, respectively. Also, the effects of particle size, functional group, and concentration range of NPs on the physiological and biochemical reactions in the living organisms were discussed. This information is helpful to more accurately understanding the underlying toxic mechanisms of NPs to aquatic biota and guiding future studies.

Early development of apoplastic barriers and molecular mechanisms in juvenile maize roots in response to La2O3 nanoparticles.

The increasing occurrence of engineered nanoparticles (NPs) in soils may decrease water uptake in crops, followed by lower crop yield and quality. As one of the most common rare earth oxide NPs, lanthanum oxide (La2O3) NPs may inhibit the relative expressions of aquaporin genes, thus reduce water uptake. In the present study, maize plants were exposed to different La2O3 NPs concentrations (0, 5, 50 mg L-1) for 72 h and 144 h right after the first leaf extended completely. Our results revealed that water uptake was reduced by La2O3 NPs through accelerating the development of apoplastic barriers in maize roots. The level of abscisic acid, determined by using ultra high performance liquid chromatography-tandem mass spectrometry, was increased upon La2O3 NPs exposure. Furthermore, ZmPAL, ZmCCR2 and ZmCAD6, the core genes specific for biosynthesis of lignin, were up-regulated by 3-13 fold in roots exposed to 50 mg L-1 La2O3 NPs. However, ZmF5H was suppressed, indicating that lignin with S units could be excluded for the formed lignin in apoplastic barriers upon La2O3 NPs exposure. The level of essential component of apoplastic barriers - lignin was increased by 1.5-fold. The early development of apoplastic barriers was observed, and stomatal conductance and transpiration rate of La2O3 NPs-treated plants were significantly decreased by 63%-83% and 42%-86%, respectively, as compared to the control. The lignin enriched apoplastic barriers in juvenile maize thus led to the reduction of water uptake, subsequently causing significant growth inhibition. This is the first study to show early development of root apoplastic barriers upon La2O3 NPs exposure. This study will help us better understand the function of apoplastic barriers in roots in response to NPs, further providing fundamental knowledge to develop safer and more efficient agricultural nanotechnology.