Effects of exogenous proline on rice seedling germination and physiological and biochemical characteristics under...

Heavy metal stress severely compromises crop productivity, with Cr(VI) being particularly detrimental to seed germination and early seedling development. This study demonstrates that exogenous proline (Pro) application significantly alleviates Cr(VI) toxicity in rice through multifaceted mechanisms. Under Cr(VI) stress (2.0-16.0 mg/L), Pro pretreatment increasing germination potential (GP) by 6.0-28.0% and germination rate (Gr) by 0.8-18.2%, while reducing mean germination time (MGT) by 6.9-14.5%; Pro elevating SOD (up to 287%), CAT (4.6-fold), and GR (1.22-fold) activities, alongside increasing GSH (1.1-fold) and AsA (1.3-fold) levels; Pro reducing MDA content by 85.0-88.2% and enhancing photosynthetic pigments (chlorophyll: 1.2-fold; carotenoids: 1.5-fold); Pro decreasing Cr accumulation in plumules by 17.5-78.5% while increasing grain sequestration. Random forest analysis revealed that Pro-mediated improvements were primarily driven by enhanced chlorophyll content (from 8.5% to 14.6%), CAT (from 13.6% to 16.7%), and SOD (from 5.1% to 8.3%) activities. These results establish Pro as an effective priming agent for improving rice establishment in Cr(VI)-contaminated environments through synergistic regulation of antioxidant systems, metal redistribution, and photosynthetic efficiency. These findings support the potential of Pro as a cost-effective strategy for improving rice establishment in Cr(VI)-contaminated soils.