Shoot Apical Meristems and Mutation: Stratified Meristems and Angiosperm Evolution

Abstract

Although apical meristems with a tunica-corpus organization occur in some gymnosperms and in practically all angiosperms, the adaptive significance of such meristems is unknown. Mathematical modeling and computer simulation studies have shown that such stratified meristems promote the long-term retention of many categories of somatic mutation (selectively advantageous, neutral, and disadvantageous). These mutations are maintained primarily as periclinal chimeras. The individual component meristems of a stratified apex have relatively small populations of apical initials. Thus, in long-lived genets, the individual component meristems of the stratified meristems of the ramets would be expected to accumulate mutations due to the operation of Muller's Ratchet. In angiosperms the accumulation of mutants and the associated loss in reproductive capacity (sexual) is compensated for by developmental selection that promotes the loss of defective genotypes without proportionate losses in reproductive capacity.