MODERATELY INCREASED CONSTITUTIVE PROLINE DOES NOT ALTER OSMOTIC-STRESS TOLERANCE

Proline-overproducing carrot cell lines were isolated by selection in medium containing hydroxyproline, a toxic analogue of proline, During growth of the cells in culture, length of lag phase, doubling time, an d maximum fresh weight were the same for the hydroxyproline-resistant cell line (HP) and the wild-type cell line (SW). Proline content and r esistance to hydroxyproline in the HP and JW lines were not strictly c orrelated indicating that another reason besides the constitutive leve l of proline is involved in hydroxyproline resistance. Tolerance to po lyethylene glycol-induced desiccation stress was not different between the two lines except perhaps at the early stages of culture growth wh en the proline levels of the two cell lines were nearly the same. The complexity of the relationship between proline accumulation and osmoto lerance is discussed and strategies to achieve constitutive high level s of proline accumulation in plants are proposed.