Physiological and Proteomic Analyses Reveal Effects of Putrescine-Alleviated Aluminum Toxicity in Rice Roots

The effects of putrescine on improving rice growth under aluminum (Al) toxicity conditions have been previously demonstrated, however, the underlying mechanism remains unclear. In this study, treatment with 50 pmol/L Al significantly decreased rice root growth and whole rice dry weight, inhibited Ca2+ uptake, decreased ATP synthesis, and increased Al, H2O2 and malondialdehyde (MDA) contents, whereas the application of putrescine mitigated these negative effects. Putrescine increased root growth and total dry weight of rice, reduced total Al content, decreased H2O2 and MDA contents by increasing antioxidant enzyme (superoxide dismutase, peroxidase, catalase and glutathione S-transferase) activities, increased Ca2+ uptake and energy production. Proteomic analyses using data-independent acquisition successfully identified 7 934 proteins, and 59 representative proteins exhibiting fold-change values higher than 1.5 were randomly selected. From the results of the proteomic and biochemical analyses, we found that putrescine significantly inhibited ethylene biosynthesis and phosphorus uptake in rice roots, increased pectin methylation, decreased pectin content and apoplastic Al deposition in rice roots. Putrescine also alleviated Al toxicity by repairing damaged DNA and increasing the proteins involved in maintaining plasma membrane integrity and normal cell proliferation. These findings improve our understanding of how putrescine affects the rice response to Al toxicity, which will facilitate further studies on environmental innovations in rice and real-world production.