Provided is a method for producing transgenic monocotyledonous plants, plant cells, plant parts, seeds, and reproduction material with modified 5-aminolevulinic acid biosynthesis. This is achieved by stably integrating one or several nucleic acid molecules coding for a protein with a 5-aminolevulinic acid synthase function (ALAS) isolated from the alpha group of purple bacteria, an active fragment thereof or an antisense or complementary sequence thereof, into tie plant genome in stable form. This method can also be used to control undesired vegetation Also provided is a method for producing transgenic plants or plant cells whose glutamate-1-semialdehyde transferase (GSAAT) expression is suppressed or inhibited by stable integration of at least one nucleic acid molecule encoding an ALAS isolated from the alpha group of purple bacteria into the plant plastome by plastid transformation.