Journal of Experimental Botany 54(392): 2553-2562 (Nov 2003)
Proline induces the expression of salt stress responsive proteins and
may improve the adaptation of Pancratium maritimum L. to salt stress

Abdel Hamid A. Khedr, Mohammad A. Abbas, Amal A. Abdel Wahid, W. Paul Quick, Gaber M. Abogadallah

Abstract

Proline is an important component of salt stress responses of plants. In this study the role of proline as part of salt stress signalling in the desert plant Pancratium maritimum L. was examined. The data showed that salt stress brought about a reduction of the growth and protein content, particularly at 300 mM NaCl, that was significantly increased by exogenous proline. In the leaves, salt stress up regulated ubiquitin, a small protein targeting damaged proteins for degradation via the proteasome, up to 5 fold as detected by western blotting. This change was also affected by proline even in non stressed leaves. However, salt stress resulted in a decrease in the amount of ubiquitin conjugates, particularly in the roots, and this effect was reversed by exogenous proline. Severe salt stress resulted in an inhibition of the antioxidative enzymes catalase and peroxidase as revealed by spectrophotometric assays and activity gels, but the activity of these enzymes was also maintained significantly higher in the presence of proline. Salt stress also up regulated several dehydrin proteins, analysed by western blotting, even in non stressed plants. It is concluded that proline improves the salt tolerance of Pancratium maritimum L. by protecting the protein turnover machinery against stress damage and up regulating stress protective proteins.