Acclimation to NaCl and H2O2 develops cross tolerance to saline-alkaline stress in Rice (Oryza sativa L.) by enhancing fe acquisition and ROS homeostasis

Plants are known to develop cross-tolerance in which plants tolerate to one stress following prior exposure to another stress. In this study, we investigated this phenomenon in rice (Oryza sativa L.) to elucidate the underlying physiological mechanisms. Twenty-one (21) day-old seedlings were pre-exposed to various concentrations of NaCl, NaHCO3, and H2O2 for 7 days and then subjected to saline-alkaline stress (SAS) for 14 days. The present findings report that pre-exposure to 10 mM NaCl and 10 mu M H2O2 develops cross-tolerance to SAS by triggering systemic physiological processes involved in Fe uptake and ROS homeostasis. While the mechanisms of this tolerance vary among pre-treatments, a consensus suggests the relevance of the following processes: (1) the ability to maintain a lower growth medium pH, (2) ability to suppress root K+ losses, (3) maintenance of a stable acquisition of Fe and P and (4) regulated generation of reactive oxygen species (ROS) via enhanced antioxidant enzyme activities. Taken together, these results are consistent with the hypothesis that a crosstalk exists between salinity stress, oxidative stress, and SAS, triggering adaptive physiological responses that develop tolerance to SAS in rice, a phenomenon that offers a prospect for developing plants tolerant to multiple stressors.