Relationship between Salinity-Induced Damages and Aging in Rice Leaf Tissues

Abstract

Segments of rice leaves at different nodal positions were incubated in NaCl solutions for various periods, and the chlorophyll content, Na content, CI content, Na/K ratio and the ultrastructure of excised leaf tissues were examined. The chlorophyll content of the leaf tissues decreased with increasing NaCl concentration and incubation period. Na and CI contents of the leaf tissues also increased with increasing NaCl concentration, but the decrease in chlorophyll content by salt stress was greater in old than in young tissues even when both tissues contained comparable amounts of Na and CI. The presence of benzylaminopurine (BAP) alleviated the salt stress-induced decrease in chlorophyll content, but did not significantly affect the element contents. Ultrastructural damages were apparent in the chloroplasts of the leaf tissues subjected to salt stress. In 0.1% NaCl-treated old leaf tissues, the thylakoids were swollen, the envelope was partly destroyed causing leakage of the chloroplast contents. However, these damages were alleviated by the addition of BAP to the NaCl solution. In young leaf tissues, the thylakoids were swollen by incubation in 1.0% NaCl solution, but no structural distortion was observed in a 0.1% NaCl solution even without BAP added. The present study suggests that the leaf tissues were damaged by an increasing salt content and became more sensitive to salt stress with advancing leaf age. BAP seemed to alleviate the damages by salt stress through retardation of leaf aging.