Polyamine and free amino acid variations in NaCL-treated embryogenic maize callus from sensitive and resistant cultivars

The effect of different NaCl concentrations on maize embryogenic calluses derived from immature embryo cultures of a) the salt-sensitive inbred line W64Ao2, b) the resistant hybrid Arizona 8601 and c) the 0.4 % NaCl pre-adapted W64Ao2 (WpA) calluses was studied. The effect of salt stress on growth as well as on polyamine (putrescine, spermidine and spermine) and amino acid contents of the treated calluses was determined. Enzymatic activities of the polyamine biosynthetic enzymes arginine and ornithine decarboxylase were also analyzed. A significant decrease in the growth of calluses in relation to increased salt concentrations and to the tolerance of the callus was observed. Embryogenic Arizona calluses showed the lowest growth inhibition and W64Ao2 calluses the highest inhibition after GO days of culture in saline medium. WpA calluses showed an intermediate response. At high-salt concentrations (1.2-2.0 %), calluses showed a significant increase in total polyamine content, especially caused by a rise in putrescine. This increase was proportionally higher for Arizona and WpA than for W64 calluses. Whereas the spermidine content of Arizona calluses was augmented with salt, a spermidine decrease was observed for W64 from 0.8 % NaCl. Arginine decarboxylase activity increased from 1.2 to 2.0 % NaCl for Arizona calluses, while in W64 calluses this increase was lower than in Arizona up to 2.0 %. With respect to free amino acid contents, the levels of free proline, which represent 50 % of the total free amino acid content, decreased with increasing salt in the medium. The highest amino acid increases were observed for arginine, alanine, glutamine, glutamic acid and gamma-aminobutyric acid. Arginine decarboxylase activity showed significant increments in relation to salt stress, which may be related to putrescine and some amino acid variations. Relationships between all the analyzed parameters and the polyamine synthesis and degradation processes under stress conditions are discussed.