A method of generating a plant tolerant of environmental stress conditions, the method comprising the step of expressing within the plant exogenous polynucleotides encoding enzymes capable of catalyzing proline production, wherein the exogenous polynucleotides are expressed in a manner so as to allow accumulation of the enzymes within a subcellular organelle of the plant. The invention further describes novel polynucleotides and nucleic acid constructs useful in implementing the methods and a transgenic plant resultant therefrom.