Abscisic acid-nitric oxide and auxin interaction modulates salt stress response in tomato roots

Integrated signaling network involving abscisic acid (ABA), nitric oxide (NO), and indole-acetic acid (IAA) controls root morphogenesis during salt stress by a mechanism still poorly understood. The present data unveiled an ABA-NO-IAA interaction underlying radicular morphological responses to salinity. Three Solanum lycopersicum genotypes were analyzed: wild type, ABA-insensitive mutant (sitiens), and auxin-responsive (DR5::GUS) plants. Nitric oxide fluorescence, nitrate reductase activity, auxin signaling, and some molecular analyses were performed. Pharmacological inhibitors and NO donor sodium nitroprusside were also used to evaluate NaCl-induced root morphological responses. Sodium nitroprusside inhibited primary root length, increased lateral root emergence, and rescued salt inhibited lateral root growth. The results showed that NO integrates the ABA-IAA signaling network of root system responses under salt stress, involving: (a) ABA and molybdenum-dependent enzymes as responsible for salt-induced NO production; (b) modulations of the plasma membrane H+-ATPase coupling and isoforms differential expression; and (c) ABA-mediated and NO-dependent antioxidative enzymes activities.