Responses to continuous and discontinuous NaCl stress of long-term cultured rice (Oryza sativa L.) cells

Rice (Oryza sativa L.) cells, grown under a continuous stress of 1.5% NaCl, produced a homogeneous mass of dry, compact, nodular callus with high regeneration potential, typical of embryogenic cultures. When transferred and subcultured in conditions without salt, the pre-adapted cells underwent several changes, leading to the formation of heterogeneous populations that comprised different cell types. This newly formed callus, in the 6-month period without salt stress, resembled cell populations of the untreated cultures. These cells are characterized by fast growth, high water content, friable texture, high salt sensitivity and low culture response. They also produce a protein pattern in the SDS-PAGE analysis, that differs from that of cells cultured under the continuous salt stress. This observation indicates that different salt stress regimes induced different responses in the cultured cells in rice.