[Effects of Combined Pollution of Microplastics and Lead on Maize Seed Germination and Growth]

Microplastics are a new contaminant that are causing worldwide concern. However, an understanding of their impact on agricultural seed germination remains inadequate. To investigate the effects of combined microplastic and heavy metal contamination on crop seed germination and growth, the effects of exposure to different single and combined concentrations of lead (Pb) and three microplastics[polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC)] on maize seed germination and growth were investigated using maize seeds. The results showed that:the inhibition of maize seed germination by Pb single exposure generally increased with Pb concentration. Compared with that in CK, 500, 1000, and 1500 mg·L-1 PE exposure significantly inhibited maize seed germination, but 100 and 300 mg·L-1 exposure had no significant effect (except at d 5). All PP concentration exposures significantly inhibited maize seed germination, with higher concentrations resulting in stronger inhibition. Compared to that under PP and PE exposure, PVC single exposure inhibited maize germination less, and 500, 1000, and 1500 mg·L-1 exposures produced a facilitative effect at the later stages of germination. The germination index, germination potential, and vigor index of maize seeds decreased with the increase in the single exposure concentration of lead and three types of microplastics, significantly decreased compared with that of CK under the combined exposure of Pb and PE, and did not change significantly under the combined exposure of PP and Pb or PVC and Pb. Among the three types of microplastics, PVC had the least effect on corn seed vigor. Both single exposures of 10 mg·L-1Pb and 100 mg·L-1 of the three microplastics promoted maize stalk and root growth, whereas other concentrations showed mostly inhibitory effects. When the PE concentration was 500 mg·L-1, the 10 and 20 mg·L-1Pb exposures both promoted maize seed stalk and root growth; however, the combined PP and Pb exposures did not produce significant inhibition, whereas 500 mg·L-1PVC and 10 mg·L-1Pb showed the strongest inhibition of maize stalk and root growth under combined PVC and Pb exposures. The effects of combined exposure to microplastics and Pb on the germination and growth of maize seeds were essentially antagonistic, thus slowing down the toxic effects of their respective single exposures on maize seeds.

Different Effects of Reactive Species Generated from Chemical Donors on Seed Germination, Growth, and Chemical Contents of Oryza sativa L

Reactive oxygen and nitrogen species (RONS) play an important role as signaling molecules in redox reactions throughout a plant life cycle. The purpose of this study was to assess how hydrogen peroxide (H₂O₂), a reactive oxygen species (ROS) and reactive nitrogen species (RNS) generated from sodium nitroprusside (SNP) and sodium nitrite, affects the germination, growth, and chemical contents of two rice cultivars (Pathum Tani and Sanpatong). The results showed that RNS generated from chemical donors and, especially, H₂O₂, enhanced the germination of the studied rice cultivars. Among the three chemical donors, H₂O₂ showed the best efficacy of the reactive species for activating early seed germination, followed by sodium nitrite and SNP. The highest percentage of seed germination rose to 99% at 6 h germination time after treatment with 25 mM of H₂O₂ for 24 h. Moreover, H₂O₂ produced a significant increase in the α-amylase activity and total soluble proteins. It was observed that a treatment with H₂O₂ on germinated seeds produced radicles with a dark blue color for longer than treatments with sodium nitrite and SNP. Our findings imply that H₂O₂ had a critical role in improving the germination and altering the chemical contents of rice seeds.