Infection with powdery mildew can enhance the accumulation of proline and glycinebetaine by salt stressed barley seedlings

Abstract

The accumulation of proline and betaine by mildewed barley in response to salt stress (range 50 to 400 m M NaCl) and the effects of stress and infection on shoot dry weight were investigated using plants grown in sand culture. In view of the dependence of proline and betaine synthesis on nitrogen metabolism, tissue contents of nitrate, amino acids and ammonium ions were also determined. Uninfected and infected plants showed similar changes in water content and osmotic potential when similar concentrations of NaCl were applied. Concentrations of NaCl above 50 m M reduced shoot dry weight, and infection increased the severity of this reduction especially at the lower concentrations of NaCl. Above 50 m M NaCl, but not at 400 m M , salt-stressed, infected plants accumulated more proline in shoots than similarly salt-stressed controls. At 400 m M NaCl, shoots of uninfected and infected plants accumulated proline to the same extent. Infection had no effect at any stage on proline levels in roots, which remained low in salt-stressed plants, Infection only promoted the accumulation of betaine at 200 mm and 400 m M NaCl. Accumulations of nitrate were only detected in salt-stressed, infected plants at 400 m M NaCl. Infection promoted the salt-induced accumulation of ammonium ions by shoots, but had no effect on the amino acid content. It is suggested that increased proline and betaine accumulation may be advantageous to the plant if these osmotica are less readily taken up by the fungus than are simple alternative organic solutes.