EFFECTORS FOR THE OSMOINDUCED PROLINE RESPONSE IN HIGHER-PLANTS

Rape leaf discs incubated in vitro in the presence of some osmoticums in concentration superior to 0.4 M (i.e. pi # -1 MPa) accumulate proli ne at a high rate after a 4 h induction period. This response provides the opportunity investigate factors involved in the control of the pr oline response. With NaCl 300 mM as osmoticum, the final amount of pro line is determined by that of sugars available in the tissues. Sucrose , D-glucose and D-fructose used as osmoticums are more efficient than mannitol and sorbitol. D-galactose proves to be a good inductor wherea s D-mannose and L-sorbose are inoperative. D-xylose induces a response whereas D (-)ribose and D (-)arabinose are inefficient. The compatibl e solutes, xylitol, arabitol, glycerol and glycine betaine induce only low amplitude responses. The role of sucrose has been particularly st udied. When proline accumulation was provoked by NaCl, this accumulati on was further enhanced by transfer to sucrose. In contrast, the sucro se induced response is inhibited by transfer to NaCl. Thus sucrose beh aves like a positive effector for proline accumultation. Its effect ca n be prevented by glycine betaine, when leaf discs are treated with th is compound before, during, or after sucrose application. Glycine beta ine behave also like an inhibitor when proline accumulation is provoke d with mannitol, PEG 6000, sodium chloride or sodium nitrate. Its inhi bitory effect was visible at concentrations between 1 and 25 mM. Dimet hyl sulfonium propanoic and pipecolic acids are also found to be poten t inhibitors of the stress induced proline response.