The technique that would be best to improve the deficiency of certain amino acids in cereals and legumes would be protein engineering. Protein engineering is a powerful tool that can be used to manipulate the amino acid sequence of proteins, including those found in cereals and legumes, to improve their nutritional content.
By modifying the genes responsible for the production of specific proteins in cereals and legumes, researchers can alter the amino acid composition of these proteins to increase the content of essential amino acids, such as lysine, methionine, and tryptophan. This can be achieved through techniques such as gene editing or recombinant DNA technology.
Plant tissue culture, vegetative propagation, and adding fertilizers to the soil are not effective methods for improving the nutritional content of cereals and legumes at the genetic level. Plant tissue culture and vegetative propagation are useful for producing large numbers of plants with desirable traits, but they do not allow for genetic modification of the plant's DNA. Adding fertilizers to the soil can improve plant growth and yield, but it does not alter the plant's genetic makeup.