Chloride is beneficial for growth of the xerophyte Pugionium cornutum by enhancing osmotic adjustment capacity under salt and drought stresses

The xerophyte Pugionium cornutum can accumulate large amounts of Cl– in its shoots for osmotic adjustment, and this is linked with improved hydration status and photosynthesis under salt and drought conditions.
Chloride (Cl–) is pervasive in saline soils, and research on its influence on plants has mainly focused on its role as an essential nutrient and its toxicity when excessive accumulation occurs. However, the possible functions of Cl– in plants adapting to abiotic stresses have not been well documented. Previous studies have shown that the salt tolerance of the xerophytic species Pugionium cornutum might be related to high Cl– accumulation. In this study, we investigated the Cl–-tolerant characteristics and possible physiological functions of Cl– in the salt tolerance and drought resistance of P. cornutum. We found that P. cornutum can accumulate a large amount of Cl– in its shoots, facilitating osmotic adjustment and turgor generation under saline conditions. Application of DIDS (4,4´-diisothiocyanostilbene-2,2´-disulfonic acid), a blocker of anion channels, significantly inhibited Cl– uptake, and decreased both the Cl– content and its contribution to leaf osmotic adjustment, resulting in the exacerbation of growth inhibition in response to NaCl. Unlike glycophytes, P. cornutum was able to maintain NO3– homeostasis in its shoots when large amounts of Cl– were absorbed and accumulated. The addition of NaCl mitigated the deleterious effects of osmotic stress on P. cornutum because Cl– accumulation elicited a strong osmotic adjustment capacity. These findings suggest that P. cornutum is a Cl–-tolerant species that can absorb and accumulate Cl– to improve growth under salt and drought stresses.