The general occurrence of “plastid initials” and their development into plastids in cortical cells of woody plants in winter

Summary

Electron microscopic studies revealed that “plastid initials”, presumed precursors of plastids, occur in cortical cells of the following plants studied in February and March: Betula ermanii Cham.; Prunus sargentii Rhed.; Pyrus communis L.; Ribes sinanense F. Maekawa; Salix matsudana Koidz. forma tortuosa Rhed.; and Sambucus sieboldiana var. miquelii Hara. Since “plastid initials” were found previously in Malus pumila Mill., Morus bombycis Koidz. and Populus euramericana cv. gelrica (Sagisaka 1991), “plastid initials” have been found in all woody plants examined to date. In P. euramericana cv. gelrica, at later stages of the development of the initials in March, the conglomerates of plastid initials became heterogeneous in terms of size, extent of thylakoid formation and ability to form starch granules. The formation of prolamellar structures was frequently observed in cells of Magnolia kobus var. borealis Sarg., which was sampled on April 19. These observations suggest the course of events in the development of the “plastid initial” and the continuity of the life of amyloplasts over a year in the life of woody plants.