Nucleic acid sequence known herein as SEQ. ID. No. 1 capable of targeting a further coding sequence to a plant plastid, method of increasing or decreasing in a plant the activity of an enzyme in the pathway of starch biosynthesis or degradation comprising the steps of stably incorporating into a plant genome a chimaeric gene comprising a nucleic acid sequence encoding a plastid targeting sequence for beta-amylase； and regenerating a plant having an altered genome, wherein the sequence of nucleic acid already comprises the mentioned sequence. A method of targeting proteins or enzymes to a plant plastid, a method of altering of enzyme in a transgenic plant, a chimaeric gene, plant cells, seed of the transformed plant and the plants.Nucleic acid sequence known herein as SEQ. ID. No. 1 capable of targeting a further coding sequence to a plant plastid, method of increasing or decreasing in a plant the activity of an enzyme in the pathway of starch biosynthesis or degradation comprising the steps of stably incorporating into a plant genome a chimaeric gene comprising a nucleic acid sequence encoding a plastid targeting sequence for beta-amylase； and regenerating a plant having an altered genome, wherein the sequence of nucleic acid already comprises the mentioned sequence. A method of targeting proteins or enzymes to a plant plastid, a method of altering of enzyme in a transgenic plant, a chimaeric gene, plant cells, seed of the transformed plant and the plants.
