Salt tolerance of Calotropis procera begins with immediate regulation of aquaporin activity in the root system.

The ability to respond quickly to salt stress can determine the tolerance level of a species. Here, we test how rapidly the roots of Calotropis procera react to high salinity conditions. In the first 24 h after saline exposure, the plants reduced stomatal conductance, increased CO2 assimilation, and water use efficiency. Thus, the root tissue showed an immediate increase in soluble sugars, free amino acid, and soluble protein contents. Twelve aquaporins showed differential gene expression in the roots of C. procera under salinity. Transcriptional upregulation was observed only after 2 h, with greater induction of CpTIP1.4 (fourfold). Transcriptional downregulation, in turn, occurred mainly after 8 h, with the largest associated with CpPIP1.2 (fourfold). C. procera plants responded quickly to high saline levels. Our results showed a strong stomatal control associated with high free amino acid and soluble sugar contents, regulated aquaporin expression in roots, and supported the high performance of the root system of C. procera under salinity. Moreover, this species was able to maintain a lower Na+/K+ ratio in the leaves compared to that of the roots of stressed plants. The first response of the root system, after immediate contact with saline solution, present an interesting scenario to discuss. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-00957-9. © Prof. H.S. Srivastava Foundation for Science and Society 2021.