Abstract: This invention pertains to novel protocols for the screening and rapid identification of compounds that specifically inhibit a predetermined enzyme or metabolic target site or pathway that is specific to plants. Enzymes which are specifically or indirected affected by the novel screens include glutamine synthetase (GS), 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAHP), dihydrodipicolinate synthase (DHPS), acetohydroxyacid synthase (AHAS) and phosphoribosyl anthranilate transferase (PAT). The enzymatic pathways targeted by the novel screening protocols are unique to plants, bacteria and fungi and are present at low levels. Thus, inhibiting these enzymes should present little or no toxicity to humans or animals. The screens provide an efficient and rapid method for assessing the herbicidal potential of test compounds. Lead compounds identified by the novel screening protocols can be used as herbicides to inhibit growth.