PHOTOSYNTHESIS IN SALT-ADAPTED HETEROTROPHIC TOBACCO CELLS AND REGENERATED PLANTS

Tobacco (Nicotiana tabacum L.) cells growing heterotrophically in the light on supplied sucrose (S0) have previously been adapted to grow in 428 mM NaCl (S25). Among the changes occurring in salinity-adapted ce ll cultures are (a) elevated levels of chlorophyll compared to unadapt ed cells; (b) decreased levels of starch; (c) alterations in chloropla st ultrastructure, including loss of starch grains, increased thylakoi d membrane structure, and the presence of plastoglobules; and (d) incr eased rates of O-2 evolution, CO2 fixation, and photophosphorylation r elative to S0 cells. These latter changes apparently derive from the f act that thylakoid membranes in S25 cells contain higher levels of pho tosystem I- and II-associated proteins as well as thylakoid ATPase com ponents. S25 chloroplasts contain immunologically detectable levels of ribulose-1,5-bisphosphate carboxylase/oxygenase, whereas S0 completel y lack the enzyme. These changes taken together suggest that even in t he presence of sucrose, S25 cells have acquired a significant degree o f salt-tolerant photosynthetic competence. This salt-tolerant photoysy nthetic capability manifests itself in plants backcrossed with normal plants for three generations. These plants contain chloroplasts that d emonstrate in vitro more salt-tolerant CO2 fixation, O-2 evolution, an d photophosphorylation than do backcross progeny of plants regenerated from S0 cultures.