Physiological effects of Na2SO4 and NaCl on callus cultures of Brassica campestris (Chinese cabbage)

Abstract

Hypocotyl‐derived callus cultures of Brassica campestris L. ssp. pekinensis cv. Kim‐jung (Chinese cabbage) were grown on Murashige and Skoog medium containing no additional salt, NaCl or Na2SO4. Na2SO4 was more than twice as inhibitory in comparison to the same concentration of NaCl when growth and fresh:dry weight ratios of established callus were measured. Levels of protein, starch, sucrose and α‐amino nitrogen were not significantly altered in salt‐grown callus. Concentrations of reducing sugars and chlorophyll were 2–3 times greater in callus grown on either salt. Proline concentration increased 15–20 fold on the highest levels of salt. Final concentrations (reached in 20–24 days) were closely correlated to the initial Na+ concentration of the medium, regardless of salt type. The osmotic potential in callus transferred to NaCl or Na2SO4 reached a maximum negative value after 16 days. For both salts, subsequent increases were correlated to increases in fresh:dry weight and growth. On both salts, turgor remained relatively constant (0. 6–0.75 MPa). Changes in Na+, K+, Mg2+ and Ca2+ content were correlated to initial Na+ concentration in the medium, not salt type. Accumulation of Na+ was accompanied by loss of K+ and Mg2+. Six to seven times less sulfate was measured in callus grown on Na2SO4 than chloride in callus grown on similar concentrations of NaCl.