Salt Stress-Induced Modulation of Porphyrin Biosynthesis, Photoprotection, and Antioxidant Properties in Rice Plants ().

Salt stress disrupts cellular ion homeostasis and adversely impacts plant growth and productivity. We examined the regulatory mechanisms of porphyrin biosynthesis, photoprotection, and antioxidant properties in salt-stressed rice seedlings. In response to 150 mM NaCl, the rice seedlings exhibited dehydration, reduced relative water content, and increased levels of conductivity, malondialdehyde, and HO. The expression levels of the salt-stress-responsive genes , , and drastically increased after NaCl treatment. The seedlings grown under NaCl stress displayed declines in /, Φ, rETR, and photochemical quenching but increases in nonphotochemical quenching (NPQ) and the expression of genes involved in zeaxanthin formation, , and . Under salt stress conditions, levels of chlorophyll precursors significantly decreased compared to controls, matching the downregulation of , , , and . By contrast, NaCl treatment led to increased heme content at 24 h of treatment and significant upregulations of , , and compared to controls. Salt-stressed seedlings also increased their expression of () and () as well as the activities of superoxide dismutase, CAT, APX, and peroxidase. Our results indicate that chlorophyll and heme biosynthesis involve the protective strategies for salt stress alleviation through photoprotection by the scavenging of chlorophyll precursors and NPQ as well as activating antioxidant enzymes.