[Sieve-tube plastids of monocotyledons : Comparative investigations of the fine structure and distribution of specific plastids].

Fine-structural investigations of 24 monocotyledons from 21 families and all but one order succeeded in revealing a plastid with cuneate proteinaceous inclusion bodies as being typical of monocot sieve-tubes. Inclusion bodies originate in large numbers during plastid differentiation; they concentrate in the matrix and aggregate around an invisible centre, that mostly lies at one end of the elongated ameboid proplastid. The inclusion-free part of the young plastid contains countless vesicles and short membranes, presumably invaginations of the inner plastid envelope. Proteinaceous inclusion bodies show a crystal-like structure composed of 50-60 Å subunits in straight and parallel order. Besides these crystal-like inclusion bodies sieve-tube plastids of many monocotyledons also contain starch. - Sieve-tube plastids of Nuphar luteum and Nymphaea alba look like plastids in dicotyledon sieve-tubes, starch being their only inclusion.