The AtCRK5 Protein Kinase Is Required to Maintain the ROS NO Balance Affecting the PIN2-Mediated Root Gravitropic Response in Arabidopsis

The Arabidopsis AtCRK5 protein kinase is involved in the establishment of proper auxin gradient many developmental processes. Among others, Atcrk5-1 mutant was reported to exhibit a delayed gravitropic response via compromised PIN2-mediated transport at root tip. Here, we report that this phenotype correlates with lower superoxide anion (O2•?) and hydrogen peroxide (H2O2) levels but higher nitric oxide (NO) content tips comparison wild type (AtCol-0). oxidative stress inducer paraquat (PQ) triggering formation O2•? (and consequently, H2O2) able rescue roots. direct application H2O2 had same effect. Under gravistimulation, correct distribution restored (at least partially) by PQ or treatment tips. In agreement, redistribution PIN2 efflux carrier similar gravistimulated PQ-treated untreated It also found PQ-treatment decreased endogenous NO level tip normal levels. Furthermore, could be reverted manipulation using an scavenger (cPTIO). potential involvement control auxin-ROS-NO-PIN2-auxin regulatory loop discussed.