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.