A process for the production of transgenic plants that have a high starch content and yield and a high amylose/amylopectin ratio. The alpha-1,4-glucan phosphorylases (GPs) catalyze the reversible cutting of bonds α-1,4 of the non-reducing ends of homopolysaccharides with at least 5 glucose molecules such as starch, maltodextrin and glycogen, leading to production of glucose-1-phosphate. The GPs in bacteria and animal cells are responsible for the breakdown of glycogen. Although the increase in GP activity leads to a reduction in intracellular levels of glycogen in bacteria and animal cells, this invention discloses the production of plants that have high starch levels and yields and high amylose/amylopectin ratio, as result of the expression of genes coding for GPs.