Stomatal regulation and adaptation to salinity in glycophytes and halophytes

Soil salinity is one of the major abiotic stresses, which negatively affects the productivity of plants in both cultivated and natural environments. Salinity stress increases osmotic stress and ROS accumulation and breaks the ionic balance in plant cells. In stomatal guard cells, these factors cause ABA biosynthesis and stomatal closure, resulting in the reduction of CO2 assimilation and crop yield loss. Halophytes are the plants capable to thrive in an extremely saline environment, thus consider as one of the vital resources for breeding salt-tolerant crops. Understanding the common and specific adaptive mechanisms to salinity of halophytes and glycophytes (most crop species) is one of the effective approaches to mining the salt tolerance-associated genetic resources. Here, we first reviewed the physiological traits conferring salinity tolerance traits (stomatal density, stomatal aperture, photosynthetic characteristics, and ion content) between halophytes and glycophytes. Comparative genomic and transcriptomic analysis of key membrane transporters regulating stomatal opening and closure is then conducted to explore the adaptation mechanisms of halophytes and glycophytes to salinity stress. In summary, future research is suggested to focus more on halophytes to gain a better mechanistic understanding of salt tolerance before applications in glycophytic crop breeding.