Effects of sodium chloride on foliar ultrastructure of sweet potato (Ipomoea batatas Lam.) plantlets grown under light and dark conditions in vitro

The effects of sodium chloride on foliar ultrastructure of sweet potato plantlets grown under light and dark conditions in vitro were examined. Ultrastructural changes induced by salt stress under light conditions occurred in the following order: (1) vacuolation, development and partial swelling of ER; (2) decrease in mitochondrial cristae and swelling of mitochondria, with an increase of the vesicles released from the Golgi stacks; (3) vesiculation and fragmentation of tonoplast; and (4) degradation of cytoplasm by the mixture of cytoplasmic and vacuolar matrices. In the mesophyll, thylakoid membranes of chloroplasts were swollen and most were lost following severe salt stress. Under dark condition, however, inner membranes of etioplasts maintained their ultrastructural integrity. The present study suggests that degradation of cytoplasm and cell organelles, except thylakoid membranes of chloroplast, occurred as a result of light-independent salt stress, and degradation of thylakoid membranes of chloroplast in the mesophyll occurred as a result of salt-induced oxidative stress.