ACCUMULATION OF A 22-KDA PROTEIN AND ITS MESSENGER-RNA IN THE LEAVES OF RAPHANUS-SATIVUS IN RESPONSE TO SALT STRESS OR WATER-DEFICIT

The response of 10-day-old seedlings of Raphanus sativus L. cv. Fakir to salt stress (100 mM to 200 mM NaCl) was investigated. Three weeks a fter initiation of salt treatment, the fresh weight of the shoots of s alt-treated plants was half that of untreated plants. The salt stress resulted in the accumulation of Na+, preferably in the old leaves. The K+ level was reduced by as much as 50% in the old leaves of NaCl-trea ted plants, whereas this reduction was only 20-25% in the young leaves . Free proline accumulated in all aerial organs, and the highest level s were found in the young leaves. Patterns of total proteins extracted from the leaves of control or salt-treated plants were compared. The most obvious change concerned a 22-kDa, pI 7.5 polypeptide, which accu mulated after exposure of the plants to NaCl. The appearance of this p olypeptide was also mediated by a rapid drought stress, and sequencing indicated that it is related to the Kunitz protease inhibitor family. A cDNA clone corresponding to the radish 22-kDa polypeptide was obtai ned and sequenced. Northern blot analysis showed that salt stress indu ces a large accumulation of this mRNA in the leaves of radish.