Extraction of Flavonoids from the Saccharification of Rice Straw Is an Integrated Process for Straw Utilization

Microbial contributions to sustainable paddy straw utilization for economic gain and environmental conservation

Paddy straw is a versatile and valuable resource with multifaceted benefits for nutrient cycling, soil health, and climate mitigation. Its role as a rich nutrient source and organic matter significantly enhances soil vitality while improving soil structure and moisture retention. The impact of paddy straw extends beyond traditional agricultural benefits, encompassing the promotion of microbial activity, erosion control, and carbon sequestration, highlighting its crucial role in maintaining ecological balance. Furthermore, the potential of paddy straw in bioenergy is explored, encompassing its conversion into biogas, biofuels, and thermal energy. The inherent characteristics of paddy straw, including its high cellulose, hemicellulose, and lignin content, position it as a viable candidate for bioenergy production through innovative processes like pyrolysis, gasification, anaerobic digestion, and combustion. Recent research has uncovered state-of-the-art techniques and innovative technologies capable of converting paddy straw into valuable products, including sugar, ethanol, paper, and fiber, broadening its potential applications. This paper aims to underscore the possibilities for value creation through paddy straw, emphasizing its potential use in bioenergy, bio-products, and other environmental applications. Therefore, by recognizing and harnessing the value of paddy straw, we can advocate for sustainable farming practices, reduce waste, and pave the way for a resource-efficient circular economy. Incorporating paddy straw utilization into agricultural systems can pave the way for enhanced resource efficiency and a more sustainable circular economy.

Antibacterial Effect of Phenolic Acids Derived from Rice Straw and in Combination with Antibiotics Against Escherichia coli

Many studies have demonstrated that natural plant extracts have inhibitory effects on microorganisms. The purpose of this study was to investigate the inhibitory effect of phenolic acids from rice straw (PAs) on Escherichia coli and their synergistic effect in combination with antibiotics. PAs can inhibit the growth of E. coli effectively by inducing the formation of H₂O₂; PA-treated cells had a tenfold greater intracellular H₂O₂ concentration than the control group. The synergistic effect caused by the interaction of PAs and antibiotics on inhibiting the growth of E. coli was significant. This effect may be caused by a PA-induced change in the permeability of E. coli cell membrane. The treatment with PAs made the extracellular K⁺ concentration reached 15 mg/L within 30 min, while the K⁺ concentration in the control group was very low and did not change significantly over time. Similarly to the extracellular K⁺, the extracellular protein concentration exceeded 150 mg/L in the PA treatment group, while it remained very low in the control group. Due to the increased cell permeability, more antibiotics can enter the cell. Hence, this study may provide a novel method of improving the safe use of antibiotics.

Tangeretin inhibits fungal ferroptosis to suppress rice blast

Flavonoids are polyphenolic secondary metabolites that function as signaling molecules, allopathic compounds, phytoalexins, detoxifying agents and antimicrobial defensive compounds in plants. Blast caused by the fungus Magnaporthe oryzae is a serious disease affecting rice cultivation. In this study, we revealed that a natural flavonoid, tangeretin, substantially delays the formation of M. oryzae appressoria and blocks the development of blast lesions on rice plants. Our data suggest that tangeretin has antioxidant activity that interferes with conidial cell death/ferroptosis, which is critical for M. oryzae pathogenicity. Tangeretin showed a ferroptosis inhibition efficacy comparable to the well-established liproxstatin-1. Furthermore, overexpression of the NADPH oxidases NOX1 or NOX2 significantly decreased sensitivity toward tangeretin treatment, suggesting Nox-mediated lipid peroxidation as a possible target for tangeretin in regulating redox signaling and ferroptosis in M. oryzae. Our nursery and field tests showed that application of tangeretin can effectively mitigate overall disease symptoms and prevent leaf blast. Our study reveals the plant-derived fungal ferroptosis inhibitor tangeretin as a potential and novel antifungal agrochemical for the sustainable prevention of the devastating blast disease in important cereal crops.

Utilization of straw-based phenolic acids as a biofugicide for a green agricultural production

Phenolic compounds inhibit phytopathogenic fungal infections effectively. In this study, the antifungal effects of rice straw-derived phenolic acids (PAs) against Fusarium oxysporum were investigated. PAs can inhibit hyphal growth and spore germination, and p-coumaric acid (CA) is the main antifungal substance in PAs. PAs could induce the formation of hydrogen peroxide and increase the relative conductivity and extracellular K⁺ concentration. Observations using Scanning Electron Microscopy, Laser Scanning Confocal Microscopy and Transmission Electron Microscopy revealed that PAs could damage membrane permeability, which caused cytoplasm leakage. This phenomenon was verified by conductivity and the release of extracellular K⁺. The chlorophyll fluorescence maps of tomato leaves suggested that F. oxysporum damaged the tomato' photosynthetic system and that PAs reduced the area infected, thereby alleviating the damage. Moreover, PAs could decrease the disease incidence of tomato fruit. The results confirmed the feasibility of using PAs as a biofungicide and provide a way to increase the value of rice straw.