The Fine Structure of Chloroplast Stroma Following Aldehyde Osmium-Tetroxide Fixation

Abstract

Markedly improved fixation of leaf tissues is obtained by means of a glutaraldehyde (or acrolein)-osmium tetroxide procedure, as compared with the results of potassium permanganate or osmium tetroxide fixation methods. The procedure has proved useful in all species so far examined. Chloroplasts are particularly well preserved. In this paper details of components of the ground-substance of Avena sativa plastids are presented. They include the following :--(i) The "stromacentre" is an area of aggregated fibrils, each 85 A in diameter, and of uncertain length. Individual fibrils may be composed of subunits. The whole aggregate is usually up to 1 # in diameter, and is visible in thin sections in the light microcope. It is present at all stages of plastid development, and, under conditions of rapid synthesis in the plastid, it may be up to 2 ~ in diameter. Evidence that it is proteinaceous is presented. Osmiophilic globules are often associated with it. (ii) Areas which resemble bacterial and blue-green algal nucleoplasms, containing fibrils approximately 30 A wide. These regions are smaller than the stromacentre and, like that structure, they occur in all stages of plastid development. Unlike it, there are several such areas per chloroplast. (iii) Particles which have some of the morphological and staining characteristics of ribosomes. Present at all stages of development, they are approximately two-thirds the size of the cytoplasmic ribosomes. They can occur in groups, thus resembling polyribosomes. (iv) The remaining material is granular, and may include dissociated portions of stromacentre material. The validity of the observations and their significance is discussed.

The Glycolytic Enzyme Phosphofructokinase-1 Assembles into Filaments

“…Data are representative of three independent cell preparations. When assembled into filaments, acetyl-CoA carboxylase (Meredith and Lane, 1978;Beaty and Lane, 1983) and β-glucosidase (Gunning, 1965;Kim et al, 2005) are enzymatically active; however, bacterial CTP synthase is enzymatically inactive in polymers, likely because of conformational constraints imposed by the filament assembly interactions (Barry et al, 2014).…”

Lipid Synthesis and Ultrastructure of Isolated Barley Chloroplasts

“…The homogenate was squieezed through 4 layers of cheese cloth an-l a 480 X g pellet removed by centrifulgation in a Sorvall RG-2 centrifuge at 2000 rpm for 1 minutte. From the supernataant a 1080 X g pellet (hereafter referred to as 1000 X g pellet) Mwas obtained by centriftuging at 3000 rpm for 10 mill- (16,38) or 0.5 M sucrose solutions (13,20) (15). These crystals or stroma centers are believed to result from damage caused by air pollutants such as organic peroxides (33).…”

Macromolecular Physiology of Plastids V

“…Chloroplast ribosomes isolated from mature leaf chloroplasts are more efficient at protein synthesis, when used in cell-free systems than the corresponding cytoplasmic ribosomes (BOARDMAN et al, , 1966. Ribosome-like particles are present in proplastids of dark grown oat leaves and believed to increase in number during chloroplast development (GUNNING, 1965). There is also some evidence that these plastid ribosomes during greening form clusters, which may be interpreted as poly-ribosomes (BROWN and GUNNING, 1966).…”