Ammonia borane enhances ion and redox homeostasis to sustain plant growth under low-potassium stress.

Despite evidence confirming the existence of naturally occurring geological and plant-derived hydrogen (H2), along with its capacity to enhance plant tolerance to various stresses, the regulatory role of H2 in plant responses to nutrient deficiency remains unclear. Here, we observed that low potassium (LK; KCl concentration decreased from 5mM to 0μM) progressively induced endogenous H2 production in Arabidopsis. To investigate the role of H2, we employed ammonia borane (AB) as an H2 donor. Further results indicated that fresh AB not only increased endogenous H2 levels, but also partially alleviated LK-induced growth inhibition, with 1mg/L being the optimal concentration. Conversely, old AB (1mg/L), used as a negative control, failed to restore the phenotype, supporting a role for AB-derived H2 in the observed responses. Subsequent evidence demonstrated that the alleviated growth inhibition and chlorophyll degradation were functionally linked to K accumulation in both shoots and roots (especially root K+ influx), further supported by the upregulated expression of K+ transporter and channel genes (AtAKT1, AtSKOR, AtHAK5, AtKUP6, and AtKUP7). Since the defective phenotypes of the genetic mutants athak5 and atkup7 were partially rescued by AB treatment, we further deduced that AtHAK5 and AtKUP7 may function downstream of H2 signaling. Furthermore, although LK stress induced redox imbalance, AB treatment significantly suppressed the accumulation of H2O2 and thiobarbituric acid reactive substances. Activities of antioxidant enzymes (superoxide dismutase and catalase) were also enhanced. Overall, these results revealed that AB reestablished ion and redox homeostasis to combat LK stress, possibly via H2.