Understanding Ameliorating Effects of Boron on Adaptation to Salt Stress in Arabidopsis

When faced with salinity stress, plants typically exhibit a slowdown in their growth patterns. Boron (B) is an essential micronutrient for plants that are known to play a critical role in controlling cell wall properties. In this study, we used the model plant Arabidopsis thaliana Col-0 and relevant mutants to explore how the difference in B availability may modulate plant responses to salt stress. There was a visible root growth suppression of Col-0 with the increased salt levels in the absence of B while this growth reduction was remarkably alleviated by B supply. Pharmacological experiments revealed that orthovanadate (a known blocker of H⁺-ATPase) inhibited root growth at no B condition, but had no effect in the presence of 30 μM B. Salinity stress resulted in a massive K⁺ loss from mature zones of A. thaliana roots; this efflux was attenuated in the presence of B. Supplemental B also increased the magnitude of net H⁺ pumping by plant roots. Boron availability was also essential for root halotropism. Interestingly, the aha2Δ57 mutant with active H⁺-ATPase protein exhibited the same halotropism response as Col-0 while the aha2-4 mutant had a stronger halotropism response (larger bending angle) compared with that of Col-0. Overall, the ameliorative effect of B on the A. thaliana growth under salt stress is based on the H⁺-ATPase stimulation and a subsequent K⁺ retention, involving auxin- and ROS-pathways.