Early stages in the development of plastid fine structure in red and far-red light

Abstract

Developmental changes in finc structure were studicd in plastids of etiolated bean leaves during the time required for thc protochlorophyllidc-chlorophyllide transformation and the following lag phase prior to chlorophyll accumulation. In agreement with some othcr workers, two distinct stages of change in the fine structure of proplastids werc found to occur upon illumination during this period. The first involves a dissociation of the previously fused units in the prolamellar bodies of the proplastids and occurs simultaneously with the protochlorophyllidc-chloroph)dlidc conversion in light of 655 m μ, but not of 682, 700, or 730 m/z. Thc effect of the rod light could not be rcversed by a simultaneously supplicd stronger far-red irradiation. The energy requirements for these structural changes parallel those for the pigment conversion. During the following step the vesicles which arose from the fused units of the prolamcllar body were dispersed in rows through the stroma, and the prolamellar bodies themselves disappeared. For these changes to occur, higher light energies were rcquircd and the leaves had to be illuminated for longer periods. A red preillumination seemed to acceleratc the development somewhat. The structural changes could be induccd by light of 655 m/z, but also, to a lesser degree, of 730 m μ. No measurablc additional chlorophyll accumulatcd during this pcriod. Thus, the structural changes obscrved were independent of major changes in pigment content. © 1964, Rockefeller University Press., All rights reserved.