A method of increasing biomass, vigor and/or yield of a plant is disclosed. The method comprises expressing within the plant an exogenous polypeptide comprising a UGGPase activity. The polypeptide may comprise an amino acid sequence at least 90% homologous, and/or at least 80% identical to SEQ ID NO: 33 as determined using the BlastP software of the National Center of Biotechnology Information (NCBI) using default parameters. Polynucleotides encoding same and plants expressing same are also disclosed.