Proline accumulation and sodium sulfate tolerance in callus cultures of Brassica napus L. cv. Westar.

Callus cultures of Brassica napus L. cv. Westar were selected which contained 5 - 6 times more proline than unselected callus. Callus pieces from these cultures were able to survive much better after subculture to medium containing 105 mM Na2SO4 than unselected callus, or unselected callus cultured on exogenous proline before or during transfer to the salt. Exogenous proline was rapidly absorbed. In unselected callus there was a peak in proline accumulation ca. 2 days after transfer to Na2SO4, followed by a decline. In contrast proline accumulation in tolerant callus was linear with time, reaching maximum levels at 8 days. Proline levels induced by exposure to salt were maintained in the absence of stress.