The recessive nuclear gene iojap of Zea mays conditions a permanent, heritable deficiency in the ability of the plastid to differentiate. iojap-affected plastids contain a normal genome as evidenced by comparison of the restriction endonuclease digestion patterns of affected and normal plastids. iojap-affected plastids contain neither detectable ribosomes nor high molecular weight RNA; the affected plastids do not incorporate exogenous amino acids into protein. The lesion in plastid ribosome content occurs early in organ ontogeny because iojap-mediated albino stripes can occupy entire clones within affected leaves.