Chloroplast Development in the Germinating Safflower (Carthamus Tinctorius) Cotyledon

Abstract

Proplastids in the mesophyll cells of the cotyledons of mature seeds of safflower are irregular in shape and compressed in narrow corners between the large inclusion bodies, oil vacuoles and protein bodies. The proplastids contain a few irregular internal membranes. During dark germination, sheets or sac‐like membranes are produced by the activity of the inner component of the proplastid envelope. These continuous membranes become reticulate and aggregate to the center of the proplastid to form after seven days' germination a quasicrystalline prolamellar body. The membranes are at first irregularly arranged and are of two sorts: those found in the interior of the developing prolamellar body, composed of laterally connected spherical profiles, and those on the periphery of the prolamellar body, which are continuous smooth sheets. The prolamellar body in these dark‐germinated proplastids reverts after 3 hr of illumination to the irregularly arranged membranous structure of the 5‐day dark germination stage. After 6 hr of illumination membranes grow from the prolamellar body forming concentric loops which, in cross section, appear as concentric circles. These membranes must be nested semi‐spheroids. Small grana appear immediately on these looped membranes close to the prolamellar body. With further illumination additional grana develop along the looped membranes in close proximity to the slowly disappearing prolamellar body. Grana increase in size and number along the looped intergranal membranes. The prolamellar body disappears after 15 hr of illumination. The interconnecting fret membranes, sparse at the 15‐hr stage, increase and after 24‐hr illumination result in the typical grana fretwork system of the mature chloroplast. Membranes are continuously being produced by the invagination of the inner member of the plastid envelope.

Changes Induced by Low Light Intensities on the Prolamellar Body of 8‐day, Dark‐grown Seedlings

“…Weier and Brown (1970) have followed the development of etioplasts in Phaseolus vulgaris from 3 to 8 days. They concurred with the report of Engelbrecht and Weier (1967) that sheets of membranes, rather than vesicles, arise from the inner component of the plastid envelope. In Phaseolus vulgaris these lamellae are porous and the prolamellar body arises through a contraction of these porous lamellae and the formation of interconnecting tubules linking each lamella to the one above it and the one below it.…”

STRUCTURE AND ULTRASTRUCTURE OF PLASTIDS IN LIGHT‐AND DARK‐GROWN ZAMIA FLORIDANA DC. SEEDLING ROOTS IN VITRO

“…Vesicles produced by the inner membrane of the plastid envelope have also been thought to contribute to thylakoid formation (Blackwell et al, 1969;Engelbrecht and Weier, 1967;Schnepf, 1980). In this study, vesicles were visible in the peripheral stroma and appeared to show contemporary continuity with the inner plastid envelope membrane.…”

“…The plastid thylakoids appeared to originate from prolamellar bodies. The origin of thylakoids from prolamellar bodies in developing chloroplasts has been reported for aspen tissue culture cells (Blackwell, Laetsch and Hyde, 1969), safflower cotyledon mesophyll cells (Engelbrecht and Weier, 1967) and sugar-cane mesophyll cells (Laetsch and Price, 1969). Prolamellar bodies have also been associated with light-induced plastid membrane formation in a variety of other angiosperms (Whatley, 1977).…”

Prolamellar Body Formation under Different Light and Temperature Conditions

“…In the dark, however, the vesicles are assembled to form a crystalline lattice structure called "prolamellar body." In the dark-grown plastids containing prolamellar body, drastic structural rearrangement of the vesicles takes place upon illumination (Eriksson et al, 1961;von Wettstein, 1958 ;Engelbrecht and Weier, 1967), while etiolated prolamellar bodies exhibit only slower response to the change of light as regards their formation from vesicles as well as their transformation into lamellae.…”