I found the following article (1) interesting because it discusses that very question. In this case the plant is Urtica pilulifera or Roman Nettle. This plant is widely used in folk medicine to treat hyperglycemia, hypertension and inflammation. The plant extract is used in ointment as an agent for skin regeneration and to treat benign prostate hyperplasia.
Amino acids are the building blocks of protein within the plant and are particularly important for cell growth stimulation. Besides being the building blocks of protein they have other life giving functions in the biosynthesis of other organic compounds such as, pigments, vitamins, alkaloids, enzymes and terpenoids. Amino acids have the greatest importance in plant nutrition for obtaining higher yields with improved quality. They give more abundant and more uniform flowering by taking part in the physiological activities of the plant. Around the root system they improve the microflora, facilitating the assimilation of nutrients. Certain amino acids are the precursors or activators of hormones and growth substances.
In recent years researchers have applied foliar sprays of amino acids and obtained remarkable enhancement in plant growth and chemical composition of some medicinal plants. Here are some of their findings:
The medicinal plant Hyocyamus muicus contains alkaloids that are useful in pharmaceuticals. It is used locally as a painkiller and a recreational drug. It’s vegetative growth was significantly increased by foliar application of the amino acids ornithine, proline and cysteine.
A popular medicinal plant, Echinacea, increased its plant weight, number of branches and root weight by application of amino acids asparatic, glutamic and tryptophan.
Ocimum basilicum commonly known as sweet basil, has been used as a traditional medicinal plant for the treatment of headaches, coughs, diarrhea, constipation, warts, worms and kidney malfunctions. Researchers found increased yield, increased plant height, fresh and dry weight of herb as well as number of branches following foliar applications of the amino acid, lysine.
Catharanthus roseus, commonly known as periwinkle, a source of drugs used to treat cancer, foliar applications of phenylalanine and methionine produced significant increment in plant height, number of branches, fresh and dry weight of plant as well as herb yield.
Turning our attention to Urtica pilulifera, foliar application of all amino acids significantly enhanced all growth parameters , plant height , number of branches , fresh and dry weight of herb and flowers and yield. Tryptophan had the highest effect on the chemical compositions, total carbohydrate (brix), lipid content and caffein acid derivatives.
Mighty Plant products are rich in amino acids for the added value they give the cultivator of medicinal gardens.
Source: Growth and chemical composition of Urtica pilulifera L. plant as influenced by foliar application of some amino acids H. E. Wahba, H. M. Motawe , A. Y., Ibrahim Medicinal and Aromatic Plants Research Dept., Pharmacognosy Dept., National Research Centre. Dokki ,Cairo,Egypt.