Merging the occurrence possibility into gene co-expression network deciphers the importance of exogenous 2-oxoglutarate in improving the growth of rice seedlings under thiocyanate stress

Using the TOPSIS method to select the best low-toxicity organic cosolvent for rice-based toxicity tests

The application of low-toxicity cosolvents in phytotoxicity tests is a common technique to enhance the distribution of non-water-soluble organic pollutants in the aqueous phase. In this study, the physiological and biochemical responses of rice seedlings to four commonly used organic solvents i.e., dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), pyridine, and Tween-80 were investigated using 16 parameters to assess their impacts on rice plants. Results from phytotoxicity tests indicated that these organic solvents caused varying toxic responses in rice plants and significantly affected the uptake and distribution of mineral nutrients within rice tissues. In order to select the best organic solvent for rice-based toxicity tests among the four solvents with optimal concentrations, the technique for order preference by similarity to ideal solution (TOPSIS) was employed to minimize the variations across different treatment groups. Three different weighting coefficients, namely entropy weight coefficients (EWCs), contribution factor coefficients (CFCs), and combination effective coefficients (CECs) were adopted to calibrate the initially created evaluation matrices. All estimations were judged by the relative closeness coefficients, in which the higher relative closeness value means the better solution to the optimal result. Among the four organic solvents evaluated by TOPSIS, pyridine at 1.24 mmol/L emerged as the most effective solution for rice-based phytotoxicity tests. Overall, this study represents the first attempt to comprehensively evaluate the toxic responses of cosolvents to rice plants using the TOPSIS method. It also offers valuable insights into a number of ecotoxicological applications like the analysis of solvent-generated extracts of environmental matrices from soils and sediments, or the detection of organic compounds induced toxicity with cosolvents.

SOS! Hydrogen Sulfide Enhances the Flavonoid Early Warning System in Rice Plants to Cope with Thiocyanate Pollution

The presence of thiocyanate (SCN-) in irrigation water has adverse effects on both plant growth and crop output. Hydrogen sulfide (H2S) is an important gaseous signaling molecule that can alleviate SCN- stress. Flavonoids are secondary compounds produced by plants and are ubiquitous in the plant kingdom. They play important roles in several physiological and biochemical processes. To investigate the effect of exogenous H2S on the growth of early rice plants under SCN- stress, we carried out a hydroponic experiment focusing on the interaction of exogenous H2S with flavonoids. In this study, a hydroponic experiment was performed to investigate the behavior of SCN- when subjected to varying effective doses (EC20: 24.0 mg/L; EC50: 96.0 mg/L; and EC75: 300.0 mg/L). The findings indicated that the relative growth rate (RGR) of the plants treated with H2S + SCN- was greater than that of the plants treated with SCN- alone. Higher amounts of flavonoids were detected in the shoots than in the roots, with more variability in the shoots. The early warning level results showed that most of the flavonoids were present at levels I and II, while quercetin was present at level IV. Genetic expression variation factor (GEVF) analyses revealed an increase in the quantity of "promoter genes" with increasing SCN- concentration in both rice tissues. Furthermore, administering external H2S while exposing rice tissues to SCN- resulted in a considerable decrease in the levels of reactive oxygen species. This study provides novel insights into the regulation of flavonoid levels in rice plants by exogenous H2S, facilitating enhanced resistance to SCN- stress and promoting sustainable agriculture.

Elucidating the intricacies of the H2S signaling pathway in gasotransmitters: Highlighting the regulation of plant thiocyanate detoxification pathways

In recent decades, there has been increasing interest in elucidating the role of sulfur-containing compounds in plant metabolism, particularly emphasizing their function as signaling molecules. Among these, thiocyanate (SCN-), a compound imbued with sulfur and nitrogen, has emerged as a significant environmental contaminant frequently detected in irrigation water. This compound is known for its potential to adversely impact plant growth and agricultural yield. Although adopting exogenous SCN- as a nitrogen source in plant cells has been the subject of thorough investigation, the fate of sulfur resulting from the assimilation of exogenous SCN- has not been fully explored. There is burgeoning curiosity in probing the fate of SCN- within plant systems, especially considering the possible generation of the gaseous signaling molecule, hydrogen sulfide (H2S) during the metabolism of SCN-. Notably, the endogenous synthesis of H2S occurs predominantly within chloroplasts, the cytosol, and mitochondria. In contrast, the production of H2S following the assimilation of exogenous SCN- is explicitly confined to chloroplasts and mitochondria. This phenomenon indicates complex interplay and communication among various subcellular organelles, influencing signal transduction and other vital physiological processes. This review, augmented by a small-scale experimental study, endeavors to provide insights into the functional characteristics of H2S signaling in plants subjected to SCN--stress. Furthermore, a comparative analysis of the occurrence and trajectory of endogenous H2S and H2S derived from SCN--assimilation within plant organisms was performed, providing a focused lens for a comprehensive examination of the multifaceted roles of H2S in rice plants. By delving into these dimensions, our objective is to enhance the understanding of the regulatory mechanisms employed by the gasotransmitter H2S in plant adaptations and responses to SCN--stress, yielding invaluable insights into strategies for plant resilience and adaptive capabilities.

Gaseous signaling molecule H2S as a multitasking signal molecule in ROS metabolism of Oryza sativa under thiocyanate (SCN-) pollution

The induction of disruption in the electronic transport chain by thiocyanate (SCN-) leads to an excessive generation of reactive oxygen species (ROS) within rice (Oryza sativa). Hydrogen sulfide (H2S) assumes a crucial role as a gaseous signaling molecule, holding significant potential in alleviating SCN--related stress. Nevertheless, there remains a dearth of understanding regarding the intricate interplay between H2S and ROS in Oryza sativa amidst SCN- pollution. In this investigation, a hydroponics-based experiment was meticulously devised to explore how H2S-mediated modifications influence the genetic feedback network governing ROS metabolism within the subcellular organelles of Oryza sativa when exposed to varying effective concentrations (EC20: 24 mg SCN/L; EC50: 96 mg SCN/L; EC75: 300 mg SCN/L) of SCN-. The findings unveiled the enhanced capacity of Oryza sativa to uptake SCN- under H2S + SCN- treatments in comparison to SCN- treatments alone. Notably, the relative growth rate (RGR) of seedlings subjected to H2S + SCN- exhibited a superior performance when contrasted with seedlings exposed solely to SCN-. Furthermore, the application of exogenous H2S yielded a significant reduction in ROS levels within Oryza sativa tissues during SCN- exposure. To elucidate the intricacies of gene regulation governing ROS metabolism at the mRNA level, the 52 targeted genes were categorized into four distinct types, namely: initial regulatory ROS generation genes (ROS-I), direct ROS scavenging genes (ROS-II), indirect ROS scavenging genes (ROS-III), and lipid oxidation genes (ROS-IV). On the whole, exogenous H2S exhibited the capacity to activate the majority of ROS-I ∼ ROS-IV genes within both Oryza sativa tissues at the EC20 concentration of SCN-. However, genetic positive/negative feedback networks emphasized the pivotal role of ROS-II genes in governing ROS metabolism within Oryza sativa. Notably, these genes were predominantly activated within the cytoplasm, chloroplasts, mitochondria, peroxisomes, and the cell wall.

Individual and mutual effects of elevated carbon dioxide and temperature on salt and cadmium uptake and translocation by rice seedlings

Plant kingdoms are facing increasingly harsh environmental challenges marked by the coexposure of salinity and pollution in the pedosphere and elevated CO₂ and temperature in the atmosphere due to the rapid acceleration of industrialization and global climate change. In this study, we deployed a hydroponics-based experiment to explore the individual and mutual effects of different temperatures (low temperature, T1: 23°C; high temperature, T2: 27°C) and CO₂ concentrations (ambient CO₂: 360 ppm; medium CO₂: 450 ppm; high CO₂: 700 ppm) on the uptake and translocation of sodium chloride (NaCl, 0.0, 0.2, 0.6, and 1.1 g Na/L) and cadmium nitrate (Cd(NO₃)₂·4H₂O, 0.0, 0.2, 1.8, and 5.4 mg Cd/L) by rice seedlings. The results indicated that Cd and Na exposure significantly (P< 0.05) inhibited plant growth, but T2 and medium/high CO₂ alleviated the effects of Cd and Na on plant growth. Neither significant synergistic nor antagonistic effects of Cd and Na were observed, particularly not at T1 or high CO₂. At increasing temperatures, relative growth rates increased despite higher concentrations of Cd and Na in both rice roots and shoots. Similarly, higher CO₂ stimulated the growth rate but resulted in significantly lower concentrations of Na, while the Cd concentration was highest at medium CO₂. Coexposure experiments suggested that the concentration of Cd in roots slightly declined with additional Na and more at T2. Overall, our preliminary study suggested that global climate change may alter the distribution of mineral and toxic elements in rice plants as well as the tolerance of the plants.