Genotypic variations in sensitivity of root K⁺ and Ca²⁺ transporters to H₂O₂ explains differential salt tolerance in wheat and barley

Wheat and barley are known as important staple food worldwide, but their growth and yield are severely affected by soil salinity, prompting a need for regaining their stress tolerance lost during domestication, to meet food security targets under current climate scenarios. The bottle neck in this process is plant phenotyping. In the past decades, approach to plant phenotyping for salinity stress tolerance was predominantly driven by the need for a high throughput screening and focused on the whole-plant level traits by advocating various non-destructive and/or analytical methods. This approach, though useful for assessing overall plant performance under salinity stress, fails to account for tissue- and cell-specific operation of contributing mechanisms and, as a result, lack the predictive power. In this work, we propose and validate a new approach for phenotyping cereal crops for salinity stress tolerance by measuring H₂O₂-induced K⁺ and Ca²⁺ flux responses from mature root epidermis. By screening 44 barley, 20 durum and 20 bread wheat accessions, we show that tolerant genotypes reduce sensitivity of cation (Na⁺, K⁺ and Ca²⁺) permeable ion channels to ROS and argue that such desensitization may allow plants to efficiently regulate its ionic homeostasis in a cell- and tissue-specific manner, without compromising stress-induced ROS signaling to downstream targets, for transcriptional regulation purposes. Being conducted on young (4-d old) seedlings, this cell-based phenotyping platform offer breeders a possibility to target new (previously unexplored) traits and may be instrumental for assisting breeders in engineering salinity stress tolerance in future breeding programs.