|
Résumé :
|
Rape leaf discs incubated in vitro in the presence of some osmoticums in concentration superior to 0.4 M accumulate proline at a high rate after a 4 h induction period. This response provides the opportunity investigate factors involved in the control of the proline response. With NaCl 300 mM as osmoticum, the final amount of proline 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 whereas D-mannose and L-sorbose are inoperative. D-xylose induces a response whereas D (-)ribose and D (-)arabinose are inefficient. The compatible solutes, xylitol, arabitol, glycerol and glycine betaine induce only low amplitude responses. The role of sucrose has been particularly studied. When proline accumulation was provoked by NaCl, this accumulation was further enhanced by transfer to sucrose. In contrast, the sucrose induced response is inhibited by transfer to NaCl. Thus sucrose behaves like a positive effector for proline accumultation. Its effect can be prevented by glycine betaine, when leaf discs are treated with this compound before, during, or after sucrose application. Glycine betaine behave also like an inhibitor when proline accumulation is provoked with mannitol, PEG 6000, sodium chloride or sodium nitrate. Its inhibitory effect was visible at concentrations between 1 and 25 mM. Dimethyl sulfonium propanoic and pipecolic acids are also found to be potent inhibitors of the stress induced proline response.
|
