Chloroplast lamellae

Phenols are present in chloroplasts (23, 24) and in vacuoles (25) of plant cells. The enzyme polyphenol oxidase and other enzymes of the phenolase complex are bound to the chloroplast lamellae or stroma 27) and in the cytoplasm (26). Although... 

J.P. Thomber, J.C. Stewart, M.W.C. Hatton and J.L. Bailey, Studies on the nature of chloroplast lamellae, II, Chemical composition and further physical properties of two chlorophyll-protein complexes, Biochemistry 6 (1967) 2006-2014. 

Figure 2. Schematic of photoinduced electron transport and phosphorylation reactions considered to occur in chloroplast lamellae [from Moreland and Hilton (2)]. Open arrows indicate light reactions solid arrows indicate dark reactions and the narrow dashed line represents the cyclic pathway. Abbreviations used PS I, photosystem I PS II, photosystem II Y, postulated electron donor for photosystem II Q, unknown primary electron acceptor for photosystem II PQ, plastoquinones cyt b, b-type cytochromes cyt f, cytochrome f PC, plastocyanin P700, reaction center chlorophyll of photosystem I FRS, ferredoxin-reducing substance Fd, ferredoxin Fp, ferredoxin-NADP oxidoreductase FeCy, ferricyanide asc, ascorbate and DPIP, 2,6-dichloropheno-lindophenol. The numbers la, lb, 2, 3, and 4 indicate postulated sites of action by...

Bend all in 1960 takes into consideration the results of many investigators and has become generally accepted as an overall description of electron flow in chloroplast lamellae. After introducing the concept of redox potential in Chapter 6 (Section 6.1 C), we will portray the energetics of the series representation (see Fig. 6-4, which includes many of the components that we will discuss next). 

Chloroplast lamellae contain different types of quinone. A quinone becomes a semiquinone when one hydrogen atom (H+ + e ) is added (a semiquinone is a free radical because of the presence of an unpaired electron) and a hydroquinone when two are added (a hydroquinone is also called a hydroquinol, or simply a quinol) ... 

One of the most striking pieces of evidence in support of the chemiosmotic hypothesis was obtained in the 1960s by Andre Jagendorf and Ernest Uribe. When chloroplast lamellae are incubated in a solution at pH 4—in which case pH1 presumably attains a value near 4 — and then rapidly transferred to a solution with a pH° of 8 containing ADP and phosphate, the... 

E Gantt and SF Conti (1966) Ultrastructure of Porphyridium cruentum. J Cell Biol 26 36-38 E Gantt and SF Conti (1966) Granules associated with the chloroplast lamellae of Porphyridium cruentum. J Cell Biol 29 423-434... 

JP Thornber, RPF Gregory, CA Smith and JL Bailey (1967) Studies on the nature of the chloroplast lamellae. I. Preparation and some properties of two chlorophyll-protein complexes. Biochemistry 6 391-395 JM Anderson, JC Waldron and SW Thorne (1978) Chlorophyll-protein complexes of spinach and barley thylakoids. Spectral characteristics of six complexes resolved by an improved electrophoretic procedure. FEES Lett 92 227-233... 

Fig. 9 shows the titration results for the following samples chloroplast lamellae and TSF-1 particles, both measured at 820 nm, and the CPI complex measured at 820 as well as 703 nm. Each sample was titrated oxidatively (starting with 100 pM ferrocyanide and adding ferricyanide to a maximum concentra tion of 10 mM) and reductively (starting with 1-5 mM ferricyanide and adding ferrocyanide to a maximum concentration of 10 mM). The titration is a plot of the light-induced AA V5. the actual redox-potential of the medium or the ferri-/ferrocyanide ratio as shown in Fig. 9. The plot of the data points clearly show that the titration was completely reversible and that P700 was in redox equilibrium with the ferri-/ferro-cya-nide couple. The solid line is the theoretical Nernst curve for a one-electron transition and the data points agree well with the theoretical course. The titration curve for both the chloroplast lamellae and the TSF-1, as well as D144 (data not shown here), yielded an value of+492 mV.

In contrast, when the CPI complex was titrated both oxidatively and reductively and monitored at both 820 and 703 nm, the data points also fell on a theoretical Nemst curve for a one-electron transition, but the results yielded a lower value of-i-427 mV, 65 mV less positive than that ofthe chloroplast lamellae or TSF-I particles. These results indicate that chloroplast particles obtained by harsher detergent treatment or samples that have been altered through aging, for example, would result in a lower redox potential. This finding probably can explain many (although perhaps not all) ofthe discrepancies in the redox-potential values reported by various groups over a period of forty years. 

P S0tifand P Mathis (1980) The oxidation-reduction potential of P-700 in chloroplast lamellae and subchloroplast particles. Arch Biochem Biophys 204 477-485... 

Chloroplast cytochrome b-559 was first described by Lundegardh 255-258) under the name cytochrome ba which had been designated as a soluble microsomal cytochrome with the a band at 559 nm 277). This cytochrome is tightly bound to chloroplast lamellae 232,241). It has been obtained by Garewal et al. 259) in 95% pure state as judged from... 

Leech arid Kirk (1968), using a differential centrifugation technique, showed the presence of NAD-dependent GDH in mitochondrial ffactions of V. faba leaves, but also NADP-linked GDH activity in chloroplast fractions. NADP-dependent enzyme was tightly bound to the chloroplast lamellae, and could not be released by osmotic shock. Isolated chloroplasts were also shown to be capable of synthesizing glutamate when supplied with 2-oxoglutarate. Lea and Thurman (1972) also showed association of GDH activity with both the mitochondrial and chloroplast fractions of Lactuca saliva. The NADH/NADPH activity ratio of the mitochondrial enzyme was 7 1, while that for the chloroplast enzyme was 1 1. Solubilization of the chloroplast enzyme required detergent treatment. Chloroplast GDH differed from the mitochondrial enzyme in its values for certain substrates, and... 

Diacylgalabiosylglycerol also contains a very high amount of linolenic acid, but palmitic acid usually represents a significant component (Table XXI). This saturated acid appears to be present at the C-2 position in higher proportions in diacylgalabiosylglycerol from plants of low taxonomic positions as well as 16 3 plants (Tulloch et al., 1973). In diacylgalabiosylglycerol from membranes other than chloroplast lamellae, the proportion of linolenic acid is significantly lower (e.g., Mackender and Leech, 1974). 

Quantosome the smallest structural unit of photosynthesis small elementary units of the thylakoid measuring 18 x 15 x 10 nm, M, 2 million, containing 230 chlorophyll molecules, cytochromes, copper and iron. Q. are obtained by ultrasonic disinte ation of isolated chloroplasts, and they can be visualized in the electron microscope. They can also be observed as granular units in the chloroplast lamella. The functional status of Q. is not clearly defined they may be involved in both electron transport and photophos-phorylation, and therefore analogous to the electron transport particles of the respiratory chain. 

Z. Combos, K. Barabas, F. Job and L. Vigh Lipid saturation induced microviscosity increase has no effect on the reducibility of flash-oxidized Cytochrome in pea thylakoids. Plant.Physiol. (1988) 335-337 B. Szalontai, M. Droppa, L. Vigh, F. Job, and G. Horvath Selectivity of homogeneous catalytic hydrogenation in saturation of double bonds of lipids in chloroplast lamellae, Photobiochem.Photobiophys. (1986) 233-240... 

The ultrastructure of Stichococcus diplosphaera in squamules of Endo-carport pusillum is very similar to that of Trebouxia. Stichococcus has a chloroplast which almost fills the cell and contains a central pyrenoid. Ten parallel chloroplast lamellae pass through the pyrenoid. Pyrenoglobuli were found at the periphery of the pyrenoid and in the stroma of the chloroplast. Starch was present also (Ahmadjian and Jacobs, 1970). 

Arntzen CJ. Dynaimic structural features of chloroplast lamellae. Curr Top Bioenerg 1978 8 111-160. 

The results of both these experiments with intact cells and our previous ones with isolated chloroplasts, can be interpreted by the following model PSI and PSII proteins are synthesized on cytoplasmic ribosomes. The PSII protein is known to be encoded in nuclear DNA. It is, therefore, reasonable to expect it to be synthesized on cytoplasmic ribosomes. The PSII protein enters the developing chloroplast and is incorporated into the growing lamellae this process is not dependent on the activity of chloroplast ribosomes. The PSI protein, on the other hand, cannot be incorporated into the chloroplast lamellae unless the chloroplast ribosomes can synthesize proteins. Perhaps one role of the chloroplast ribosomes is to synthesize proteins, such as peak D, which are concerned with immobilizing proteins entering the chloroplast from the cytoplasm PSI protein and cytochrome / are two such entering proteins. 

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