Provided are methods of increasing tolerance of a plant to abiotic stress, and/or increasing biomass, growth rate, vigor and/or yield of a plant. The methods are effected by expressing within the plant an exogenous polynucleotide encoding a polypeptide comprising an amino acid sequence at least 90% homologous to the amino acid sequence selected from the group consisting of SEQ ID NOs:201, 207, 212, 202-206, 208-211, 213-391, 1655, 961-1529, and 1660-1663. Also provided are polynucleotides, nucleic acid constructs, polypeptides and transgenic plants expressing same which can be used to increase tolerance of a plant to abiotic stress, and/or increase biomass, growth rate, vigor and/or yield of a plant.