Salinity Tolerance in Sorghum. II. Cell Culture Response to Sodium Chloride in S. bicolor and S. halepense

Abstract

Grain sorghum (Sorghum bicolor (L.) Moench], is reported to be less tolerant to salt than the noxious weed and potential biomass energy crop, johnsongrass [S. halepense (L.) Pers.). The objective was to compare callus growth and osmotic responses to salinity of these two sorghum species. Callus was grown for 2 wk in a liquid Murashige and Skoog medium to which NaCl was added to final concentrations of 0.05,0.1, and 0.15 M. Relative fresh weight growth of callus in response to increased salinity in the culture medium was greater in S. halepense than in S. bicolor. After 2 wk of NaCl treatment, brown coloration and apparent necrosis were observed on callus of S. bicolor but not on that of S. halepense. The Na/K ratios were lower in callus of S. halepense than that of S. bicolor at all NaCl concentrations. Total amino acids in salinized callus did not change, but proline increased; this increase was greater in S. halepense callus than in that of S. bicolor. Levels of Na and Cl were larger in S. halepense callus treated with 0.1S mM NaCl and these were associated with a ψp of 0.40 MPa, whereas a ψp of 0.26 MPa was observed in callus of S. bicolor. Accumulation of NaCl accounted for three‐fourths of the solutes involved in osmotic adjustment in the callus of both species. Growth and Na/K ratios in salinized callus in this study were correlated with whole plant responses determined in another study. Callus growth and Na/K ratios could therefore be used as indicators of whole plant salt tolerance in Sorghum.