Abstract
This study combines electrophysiological, imaging, and molecular techniques to compare reactive oxygen species (ROS)-mediated K+/Na+ regulation in the root elongation zone (EZ) and mature zone (MZ) of halophytic quinoa (Chenopodium quinoa) and glycophytic spinach (Spinacia oleracea). Under salinity stress, quinoa exhibited transient ROS (H2O2) accumulation followed by rapid recovery, whereas spinach showed prolonged oxidative stress and severe ionic imbalance in roots. Quinoa plants avoided cytosolic Na+ toxicity by excluding Na+ via the up-regulation of salt overly sensitive (SOS1) genes and enhanced vacuolar sequestration via NHX. Quinoa maintained K+ homeostasis under ROS through biphasic regulation linked to tissue-specific expression of K+ transporter genes GORK, AKT1, HAK5, and KEA, while spinach experienced a sustained K+ loss. Transcriptomic analysis revealed robust induction of MAPK signalling and ethylene-related genes in quinoa, contrasting with the reliance of spinach on abscisic acid and delayed antioxidant responses. Overall, the differential sensitivity of root zones was attributed to the spatially restricted ROS signalling in quinoa, which fine-tunes ion transporter activity, while spinach showed excessive ROS production and K+ loss. These results demonstrate that the oxidative tolerance of quinoa arises from coordinated ROS-hormone-transporter interactions in a highly tissue-specific manner, providing a mechanistic framework for improving crop resilience.