Prolamellar bodies

PARK H, KREUNEN s s, cuTTRiss A J, DELLAPENNA D and POGSON B (2002) Identification of the carotenoid isomerase provides insight into carotenoid biosynthesis, prolamellar body formation and photomorphogenesis . Plant Cell, 14, 321-32. 

In 1980 it was pointed out that the prolamellar body is a perfect example of a Cp structure [4]. (Later, more detailed, analyses have revealed that it may also be a Cd structure cf. section 7.2.) Following work on the structure of cubic phases, it was also realised that two-dimensional analogues are possible. This in turn suggested that a phase transition involving changes in the intrinsic curvature of membranes might be possible [29, 30]. Such a mechanism has far reaching implications. Clear evidence for such transitions between bilayer conformations has been reported [9]. This membrane bilayer model will be described below. 

The whole prolamellar body thus has the structure of a cubic phase, as discussed in detail in Chapter 7. 

Other possible areas of application of the periodic surfaces, or of disordered relatives of these, include structure of superconductors in the intermediate state (Shal nikov 1941), sintering kinetics (Hench and Ulrich 1984), fluid flow through porous media (e.g., Zick and Homsy 1982), the topology of spacetime at the scale of Planck length (Wheeler 1957), the structure of the prolamellar body in certain plastics (Gunning 1965), certain phase-segregated block copolymers (Thomas et al. 1986 Anderson and Thomas 1988)) semiconductor-... 

The fact that we can observe photoreduction already in 1-day old leaves with similar kinetics as in older leaves shows that the formation of the active Pchlide does not require long etiolation periods and is not correlated directly with the formation of the prolamellar body since the latter is only detected after 3 days (17). 

Antibodies to iTOR Rabbits were immunized with the enzyme isolated from prolamellar bodies of 7-day-old etiolated barley leaves and purified by chromatography on DEAE-cellulose in the presence of exogenous NADPH and protoohlorophyllide (Pchlde) /5/ For ELISA, either rabbit antiserum diluted in the ratio of 1 8 (Pig.l) or the fraction of immunoglobulin a isolated from the antiserum on DEAE-cellu-lose 6ind diluted several times (Pig. 2) were used. 

In etiolated leaves the majority of PChlide is connected to the PChlide reductase enzyme which, according to the ternary complex model, bounds NADPH molecule(s), too (4). This complex is an integral unit of prolamellar bodies (PLB) and in vivo can be characterized with a 650 nm absorption and 657 nm low-temperature fluorescence emission maximum (5). However, PChlide or PChl molecules must be connected to other components of the etioplast inner membranes, these molecules can regenerate the phototransphormed PChlide or cannot be phototransformed at all (2). These molecular complexes have absorption maxima at 628-630 and 635-637 nm (6). 

The Phase Structure of Galactolipids and Their Role in the Formation of the Prolamellar Body 843... 

There were two increases in novo synthesis of fatty acids during greening of Avena leaves (Fig.lA). The first rise occurred 3 hour after illumination in which the prolamellar bodies are degenerated. The second... 

ELECTRON MICROSCOPY AND X-RAY SCATTERING STUDIES OF THE STRUCTURAL ORGANISATION OF PROLAMELLAR BODIES ISOLATED FROM Zea mays. 

Etioplasts, the plastids in leaves of dark-grown seedlings, are more or less uniform at the same stage of immaturity. They generally contain one or two paracrystalline, prolamellar bodies (Fig. 2). They occasionally have a few more vesicular-looking membrane structures within them and, like mature chloroplasts, contain ribosomes and DNA. The etioplasts also contain a small amount of a near precursor of chlorophyll a called protochlorophyllide a. 

Dramatic structural changes occur within the chloroplast during greening. The paracrystalline prolamellar body becomes disorganized into... 

Fig. 2. Electron micrograph of an etioplast in thin section. Leaf tissue from a dark-grown Zea mays plant was fixed and stained as in Fig. 7.1. Many ribosomes are seen in regions marked R. Regions marked PB show the paracrystalline prolamellar body. Strands of DNA are seen in the clear areas below each D not all the sites of DNA are marked.

Table IV. Molecular Weights of the Most Prominent Polypeptides in Prolamellar Bodies and Thylakoids of Maize Plastids... 

Polypeptide number Nominal molecular weight Prolamellar bodies of etioplasts Plastid membranes after 4 cycles of illumination Thylakoids of chloroplasts Changes during development of thylakoids from prolamellar bodies... 

Unlike the prolamellar body of higher plants, the structure found in Chlamydomonas has a noncrystalline disorganized core (Fig. lOB), which does not show fast changes and is not completely transformed into thylakoids, even after several hours of illumination. ... 

Finally, the response to illumination of the prolamellar body-like structure present in the dark-grown cells is extremely sluggish a fact which... 

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