Structure, composition, and distribution of plastid nucleoids in Narcissus pseudonarcissus

Abstract

The size, frequency and distribution of the nucleoids of chloroplasts (cl-nucleoids) and chromoplasts (cr-nucleoids) of the daffodil have been investigated in situ using the DNA-specific fluorochrome 4'6-diamidino-2-phenylindole. Chromoplasts contain fewer nucleoids (approx. 4) than chloroplasts (> 10), and larger chromoplasts (cultivated form, approx. 4) contain more than smaller ones (wild type, approx. 2). During chromoplast development the nucleoid number decreases in parallel with the chlorophyll content. Each nucleoid contains 2-3 plastome copies on average. In chloroplasts the nucleoids are evenly distributed, whereas they are peripherally located in chromoplasts. The fine structure of isolated cl-and cr-nucleoids, purified either by Sepharose 4B-CL columns or by metrizamide gradients, was investigated electron microscopically. The cl-nucleoids consist of a central protein-rich core with 'naked' DNA-loops protruding from it. In cr-nucleoids, on the other hand, the total DNA is tightly packed within the proteinaceous core. The protein-containing core region of the nucleoids is made up of knotty and fibrillar sub-structures with diameters of 18 and 37 nm, respectively. After proteinase treatment, or incressing ion concentration, most of the proteins are removed and the DNA is exposed even in the case of cr-nucleoids, the stability of which proved to be greater than that of cl-nucleoids. The chemical composition of isolated plastid nucleoids has been determined qualitatively and quantitatively. Chromoplast-nucleoids contain, relative to the same DNA quantity, about six times as much protein as cl-nucleoids. Accordingly the buoyant density of cr-nucleoids in metrizamide gradients is higher than that of cl-nucleoids. In addition to DNA and protein, RNA could be found in the nucleoid fraction. No pigments were present. The cr-and cl-nucleoids have many identical proteins. There are, however, also characteristic differences in their protein pattern which are possibly related to the different expression of the genomes of chloroplasts and chromoplasts. Nucleoids of both plastid types contain some proteins which also occur in isolated envelope membranes (probably partly in the outer membrane) and thus possibly take part in binding the DNA to membranes.

New insights into plastid nucleoid structure and functionality

“…Initial reports from electron microscopic studies, which showed that the de-proteinized spinach plastid chromosome is organized in a folded form around a central body composed of proteins which are not extractable by usual procedures (Herrmann et al 1974;Yoshida et al 1975), were soon followed by biochemical data that confirmed the observation that proteins are either firmly bound to DNA in a central region or are more loosely bound to the peripheral DNA fibrils. These observations led to the proposal of a layered structure of plastid nucleoids (Briat et al 1982;Hansmann et al 1985; reviewed by Sakai et al 2004) (see Fig. 1).…”

“…An estimated 30-50 % of the ptDNA is incorporated in the central body. Surprisingly, ultrastructural studies revealed that the DNA loops protruding from the core of chloroplast nucleoids are lacking in nucleoids from chromoplasts of Narcissus pseudonarcissus (Hansmann et al 1985). Even though this indicates that the layered structure is not static but rather under developmental control, it is unclear what determines the relative proportions and degrees of compaction in the nucleoid layers and whether the observed changes have functional consequences.…”

Expression of Amyloplast and Chloroplast DNA in Suspension-Cultured Cells of Sycamore (Acer pseudoplatanus L.)

“…In view of the fact that amyloplasts are the sites of starch synthesis in storage organs such as seeds and roots (21), it is imperative to examine the structure and function of the amyloplast genome and to elucidate the regulatory mechanism(s) which control its expression (10). It is frequently postulated that amyloplasts and chloroplasts are ontogenically related (9), although neither the functional nor the structural nature of the former organelle has been substantively characterized in comparison with that of the latter which has been studied by numerous ' Supported by the grants from the Mnistry ofEducation, Science and Culture (Monbusho) (6,7,22).…”

“…It is thus reasonable to conclude that the amyloplast DNA in the wild sycamore cells is not actively transcribed. Hansman et al (10) have sus that DNA of the chromoplast, another type of differentiated plastid, is also not active.…”

DNA Methylation Occurred around Lowly Expressed Genes of Plastid DNA during Tomato Fruit Development

“…The transformation of etioplasts (proplastids) to chloroplasts upon illumination of dark-grown seedlings and that of chloroplasts to chromoplasts in fruit tissues, such as tomato and Capsicum spp., are well characterized examples of organelle differentiation (1, 3,6,7,19,20,26). Several investigators have reported that the restriction profiles of DNA isolated from the chromoplasts are identical with those of chloroplast DNA (6,8,9,24).…”