Conclusion
Based on our data and the extended literature, we put forward a model describing aspects of salinity tolerance in pistachio with respect to root developmental gradient. Pistachio roots contain both endodermis and exodermis as apoplastic barriers (Fig. 6). During salinity stress, enhanced suberin deposition at these barriers, particularly in the endodermis, and vacuolar sequestration both are associated with the high salinity tolerance genotype.
This is a foundational study for the examination of pistachio root plasticity using fluorescence confocal microscopy across a fine root developmental gradient. Together, our study illustrates the importance of including different stages of development in evaluating stress tolerance mechanisms. It also suggests that both development and cell type specificity is another layer of complexity that should be taken into account in salinity stress response.
The data presented here provide a model to be considered for future investigation of the cellular mechanisms of salinity tolerance, with additional potential application for analyzing within species variation of salinity tolerance for plant breeding purposes. Woody perennial nut species, such as pistachio, provide useful examples of natural adaptation in abiotic stress that can be further utilized for a mechanistic understanding of this process. With the anticipated availability of the pistachio rootstock genomes, the aforementioned mechanisms can be uncovered at a molecular level in future studies.