Compositions including phenylalanine, analogues, and phenylalanine precursors protect plants against environmental stressors. Delivery systems and methods of treating are provided. A method of protecting plants against environmental and/or biological stressors includes administering a composition including phenylalanine, a phenylalanine precursor or other skikimate pathway or phenylpropanoid pathway compound, or an amino acid that can be converted to phenylalanine to at least one root, at least one germinating seed, or at least one epidermal surface of a plant. Administration of the composition to the root, seed, or plant improves or restores at least one growth characteristic of the plant when the plant is exposed to an environmental stressor such as ultra-violet radiation, cold, drought, salt, heat, fungus, beetles (e.g., Japanese beetles), hormones, bacteria, arthropods, and worms (e.g., soybean cyst nematode) or products of biotic organisms. Another method of protecting plants against environmental and/or biological stressors includes coating a plant (e.g., soybean) seed with a composition including phenylalanine, a phenylalanine precursor or other skikimate pathway or phenylpropanoid pathway compound, or an amino acid that can be converted to phenylalanine such that the composition protects the seed and a plant that grows from the seed from ultra-violet radiation, cold, drought, salt, heat, fungus, beetles (e.g., Japanese beetles), hormones, bacteria, arthropods, and worms (e.g., soybean cyst nematode) or products of biotic organisms. Plants and plant cells including an isolated nucleic acid encoding at least one prephenate dehydratase operably linked to a promoter are described herein.