7S Globulins of Cereals

Abstract

Storage proteins of the 7S globulin class have been identified in seeds of a number of cereals. In contrast to the situation in legumes, however, these proteins are present in relatively small amounts in cereals. In those cases where they have been examined, the cereal 7S globulins accumulate primarily in the embryo and aleurone layer (Yupsanis et al., 1990). This is in contrast to the situation with the prolamins, the primary storage proteins of most cereals, which accumulate in the starchy endosperm. The 7S cereal globulins probably serve a role as seed storage proteins, and their hydrolysis during germination may provide an immediate source of nitrogen and carbon to the young seedling (Khavkin et al., 1978; Kriz, 1989). Their role as storage proteins is consistent with the observation that in maize mutants such as opaque2 and floury2, which condition a reduction in grain prolamin content, the levels of globulins are increased relative to those in normal seeds (Puckett and Kriz, 1991; Dierks-Ventling, 1982). It is presumed that this increase in globulins occurs to compensate for the decrease in levels of the primary storage proteins in the seed. The globulins are, however, not absolutely required for normal seed functions, as maize mutants completely lacking in 7S globulins exhibit normal patterns of seed development and germination (Kriz and Wallace, 1991).