Ultrastructural effects of salinity in Nicotiana bigelovii var. bigelovii callus cells and Allium cepa roots

Salinity stress has been studied in two different plant systems such as Nicotiana bigelovii callus and Allium cepa roots in regard to its toxic effect on cells at ultrastructural level. Various types of cell damages have been observed either in N. bigelovii callus or in A. cepa root apices. However, differences in cell response have been found between these two plant tests. Callus Cells appeared more tolerant to salt in comparison with root meristematic cells. In the first plant system the more relevant effect was seen in the chloroplasts which lost the capacity to synthesize starch contrarily to control and, especially, exhibited strong alterations in the thylakoidal structure. Changes at nuclear and cytoplasmic levels were also observed. In A. cepa root meristem cells more severe damages were induced by the salt. In this case, very strong alterations such as plasmolysis processes, disorganization of nuclei and cytoplasm content were observed. Moreover, in both plant systems a considerable growth decrease occurred. The results are discussed in regard to the underlying mechanism of salt stress.