Physiological and ultrastructural responses of Catharanthus roseus cell suspension to salt stress

Catharanthus roseus (L.) cell response to salinity was investigated. Seven days after cell treatment with 100 mM NaCl, they showed a decrease in dry weight and an increase in sodium and chloride contents (about 12.4- and 1.5-fold, respectively, in comparison to the control). At the ultrastructural level, NaCl treatment reduced cell size and increased plastid density. In addition, it reduced the starch grain size and their number per plastid; however, starch content was 1.5-fold increased, which was due to the increase in the plastid density. At the ultrastructural level, the applied salinity had no obvious effects, such as swelling or disorganization of plastids except a slight decrease in the stroma electron density. Equally, no deleterious effect was observed on mitochondria except a small increase of their crista volume and matrix electron density. It was shown that, although the relative sensitivity of C. roseus cells to salt stress pointed by the reduction in the dry weight, a decrease in the cell size, and the high accumulation of toxic ions, they preserved the integrity of their plastids and mitochondria.