Amino acids in plants: regulation and functions in development and stress defense

In the last decades, the importance of amino acids in plant development and stress defense has become increasingly evident, attracting growing interest in basic and applied plant science. Here we present novel findings on amino acid research and propose a picture, as up-to-date as possible, of the current knowledge on this fascinating aspect of plant physiology. Besides being building blocks for protein synthesis, many amino acids, including some not involved in protein synthesis, turned out to have active roles in plant development and participate in the plant’s response to environmental stresses. In addition, amino acids serve as precursors for many primary and secondary metabolites and have pivotal roles in human nutrition, either as a source of nutraceutical compounds or as essential dietary components. Indeed, nine out of twenty-one proteinogenic amino acids cannot be synthesized in animals, including human beings, and three or more others are not synthesized in sufficient quantities to satisfy the metabolic needs . These nutritionally essential amino acids must be taken up from the diet and by far the greatest share is derived from plants. In contrast to humans and animals, plants synthesize all twenty-one proteinogenic amino acids themselves