Introduction
Grape is one of the most important horticultural crops and economically produced in world and Iran which is cultivated in a wide range of climatic conditions. Duo to the difficulties of cultivating grape is its relatively sensitive to salinity stress. Salinity can cause significant anatomical changes in the internal tissues of plant organs. The effect of using low-quality water on the anatomical structure of grapevine organs has not yet been studied. This study aimed to evaluate the structural behavior of roots, stems, leaves, petioles, and main veins of grape leaves in Yaghooti cultivar under progressive salt stress.
 
Materials and Methods
This study was carried out based on a completely randomized design with three replications during two consecutive years 2020-2021. Salinity treatment at four levels, including zero (control), 25, 50, and 100 mM NaCl on one year old rooted cuttings under greenhouse conditions. Plant various organs consisting of roots, stems, leaves, petioles, and main veins were microscopically investigated through the conventional methods of sampling, fixing, sectioning and staining.
 
Results and Discussion
In the stem, the epiderm thickness increased until 50 mM level, and decreased in 100 mM level. In 100 mM, sclerenchyma thickness, pith diameter, and vascular bundles number increased, while collenchymas thickness, cambium, phloem, metaxylem, protoxylem, and stem cortex decreased. In the root, cortex thickness reduced, but the vascular bundles’ thickness, their number, as well as pith and vascular cylinder diameters increased, and more periderm thickness as well as the centralization of xylem vessels toward pith tissue were observed. In the petiole, in 100 mM level, an increase in sclerenchyma thickness and vascular bundles number was observed along with a decrease in phloem thickness, cambium, metaxylem, protoxylem, and cortex. In the leaf and main vein, palisad parenchymal cells became smaller and denser with an increase in their number; furthermore, a decrease in spongy parenchymal cells thickness along with the increase of their intercellular space and the increase of epiderm thickness were observed. In addition, vascular bundles number, sclerenchyma thickness, and pith diameter increased, while the decrease of vascular bundles’ thickness and collenchymas thickness was found in the main vein. Moreover, a large number of salt crystals were observed in all the plant organs, especially in the roots.
 
Conclusion
Overall, the results of this study revealed that salinity stress caused changes in the anatomical structure of roots and various aerial organs in Yaghooti grapevine saplings. It appears that at a stress of 100 mM salinity, the increase of epiderm and sclerenchyma thickness in the aerial organs contributed to preventing transpiration and preserving water content. Besides, periderm thickness at the root as a physical barrier to further absorption, transport of soluble substances, and protection of vascular cylinders helped the plant to tolerate salinity conditions. In addition, a large number of vascular bundles were involved in the secondary uptake of salt in the surrounding parenchymal cells. Therefore, most of the anatomical changes in the studied organs can be considered as a kind of adaptation to increase the chances of the plant survival against salinity.