Inhibition of Seed Germination in Portulaca oleracea L. by Rhus typhina L. Extract Is Mediated via Suppression Activities of Amylase Rather than Antioxidative Enzymes.

Rhus typhina L. is widely recognized as a landscape ornamental plant and its extracts have demonstrated biological activity against multiple weed types. This makes it a promising candidate in sustainable agriculture as a bioherbicide by offering a solution to mitigate the growing problem of herbicide resistance. Therefore, this study was designed in agar culture to analyze the effect of powders of the branch, fallen leaf, and pericarp from Rhus typhina L. against seed germination of Portulaca oleracea L. and evaluate its inhibitory mechanisms based on anatomical structure and the activities of antioxidative enzymes, α-amylase, and β-amylase. The main allelopathic compounds were also identified based on high-performance liquid chromatography-mass spectrometry (LC-MS), and their bioherbicidal effects were evaluated. Brassica napus L. was used as the object for biosafety evaluation. The results showed that the seed germination of Portulaca oleracea L. under treatment with powder extract from Rhus typhina was inhibited by exhhibting swelling and deformation in endosperm cells and chaotically scattered starch granules in seed embryos with a shorter radicle length than the control. During the period of treatment, antioxidative enzymes were quickly activated to scavenge the suddenly surging reactive oxygen species (ROS) as a measure of boosted malonaldehyde (MDA) content. Antioxidative enzyme (POD, SOD, and CAT) activities were also activated to mitigate the oxidative damage. In contrast, both α-amylase and β-amylase activities were significantly suppressed. A total of 16 allelochemicals were identified in the branch, fallen leaf, and pericarp of Rhus typhina L. Among these, gallic acid, methyl gallate, and tyrosol were identified as exhibiting the most significant inhibitory effect during the whole germination process of Portulaca oleracea L., resulting in browned seedlings and stunted radicle length compared with the control, while far weaker inhibitory effects were found against Brassica napus L. In summary, extracts from Rhus typhina L. targeted α-amylase and β-amylase activities rather than antioxidative enzyme activities to inhibit the germination of Portulaca oleracea L. Gallic acid, methyl gallate, and tyrosol were the key compounds that inhibited its germination.