Despite wide variation in their detailed structures, all seed storage
proteins have a number of common properties. First, they
are synthesized at high levels in specific tissues and at certain
stages of development. In fact, their synthesis is regulated
by nutrition, and they act as a sink for surplus nitrogen. However,
most also contain cysteine and methionine, and adequate
sulfur is therefore also required for their synthesis. Many seeds
contain separate groups of storage proteins, some of which
are rich in sulfur amino acids and others of which are poor