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 signi®cantly 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 signi®cantly 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.