Thylakoid system

Photosynthesis in all photosynthetic organisms is blocked by triazines, as well as by other PS II herbicides, when isolated thylakoid systems are tested. However, in intact plants, they express either different inhibitory potency or no inhibition. This shows that the specificity of these photosynthesis herbicides to certain weeds is not related to a difference in the chemistry of their primary target, but rather is attributed to degradative mechanisms, translocation, and translocation mechanisms. 

Colligative Protection. The principles of colligative protection were first outlined by Lovelock (35) for the red blood cell. These principles are also valid for the thylakoid system (14,21,68). If only one solute is present in a membrane suspension, its concentration, regardless of its initial concentration, will rise dining freezing to a level determined solely by the final freezing temperature. If the solute is a cryotoxic compound, this final level may be sufficient to cause membrane inactivation. When several solutes are present and only one is a cryotoxic solute, the same... 

Thomasset B, Friboulet A, Barbotin JN et al. Modulation by a high citrate concentration of kinetic parameters and of functional stability of two immobilized thylakoid systems. Biotechnol Bioeng 1986 28 1200-1205. 

In photosynthesis, ADP is phosphorylated uid NADP reduced at the expense of light energy. The NADPH and ATP formed by the chloroplast thylakoid system serve to reduce OO2 in the chloroplast stroma. The product of the phosphorylation potential (ATP/ADP Pj ) and the redox ratio (NADPH hVnadp ) is termed assimilate force (Fj ). It is instrumental in driving carbon reduction. The reaction... 

Mineral deficiency strongly affects the development of leaves and of the photosynthetic apparatus. We were interested to know whether carbon flux is more restricted in mineral deficient leaves by the thylakoid system or the Calvin cycle. Spinach was grown under mineral deficiency as shown in Tab. 1. Leaves of different age were detached and photosynthesis and F was measured. Rates of photosynthesis were on a unit leaf area basis consistently higher in the control leaves than in leaves deficient in phosphorus, sulfur or nitrogen. Sulfur and old nitrogen deficient leaves were chlorotic. F was increased under all deficiency conditions and particularly so in old leaves of phosphate and nitrogen starved plants and in young leaves of sulfur-deprived plants. The increase in F clearly correlated with the development of pronounced deficiency symptoms and reduced rates of photosynthesis. The data indicate that mineral deficiency introduces flux limitations in the Calvin cycle. 

Because both oxidative and photophosphorylation occur at large sub-entities in organelles of heterotrophic and autotrophic cell, the plasma membrane, the mitochondria inner membrane or the chloroplast thylakoid system, and in a cooperative fashion - one thylakoid contains about 10 CF CF complexes -, in reconstitution experiments the danger of misinterpretation is always inherent The reappearence of catalytic activity of the membrane system may be due to "structural reconstitution", i.e. repair of H leakeness by the added soluble component (Schatz et al., 1967, McCarty, Racker, 1967). 

DEVELOPMENT OF A CHEMILUMINESCENCE DETECTION OF HERBICIDES RELATIVE TO THE MEDIATED INHIBITION OF THYLAKOIDS IN A ji-FLUIDIC SYSTEM... 

Plant cells contain a unique family of organelles, the plastids, of which the chloroplast is the prominent example. Chloroplasts have a double membrane envelope, an inner volume called the stroma, and an internal membrane system rich in thylakoid membranes, which enclose a third compartment, the thylakoid lumen. Chloroplasts are significantly larger than mitochondria. Other plastids are found in specialized structures such as fruits, flower petals, and roots and have specialized roles. 

Characteristic of all chloroplasts, however, is the organization of the inner membrane system, the so-called thylakoid membrane. The thylakoid membrane... 

The vertebrate retina contains two classes of light-sensitive receptor cells called rods and cones. The rod is an elongated cylindrical cell containing several hundred thylakoids which support the visual pigment. The pigment system in the rod is confined to internal membranes situated close to the outer membrane of the cell. In the other type of visual receptor, the cone, the pigment is situated in the external membrane itself. In the cone the external... 

Fig. 10. Redox systems of the photosynthetic electron transport chain incorporated in the thylakoid membrane. Irradiation causes the generation of a proton gradient (after Trebst and Hauska135))...

The physical separation of PS II and PS I permits the chloroplasts to respond to changes in illumination. The relative amount of light absorbed by these two systems varies with the distribution of light harvesting complexes (LHCs) between the stacked and unstacked portion of the thylakoid membrane. 

For the formation of one 02 molecule four electrons have to be transferred. This requires a "quantum storage device". In the photosynthetic system of green plants this is achieved with two photosystems that are linked through an electron transport chain, Fig. 10.2, and by means of the thylakoid-membrane that enables the separation of the photoproducts 02 and the reduced form of nicotinamide adenine dinucleotide phosphate, NADPH. 

Most of the arguments described in the sections on bacterial signal peptides and membrane proteins seem to be valid for the eukaryotic systems, as well as the translocation phenomena across the ER membrane (Sakaguchi, 1997). They seem to be also true for the translocation system across the mitochondrial inner membrane protein into the intermembrane space and the system across the thylakoid membrane in chloroplasts. Although the TAT-dependent pathway has not been found in the ER, it exists on the thylakoid membrane (and possibly on the inner membrane of mitochondria). 

Chloroplasts are a typical type of plastid that performs various metabolic reactions as well as photosynthesis. Their envelope consists of two membranes the outer envelope membrane and the inner membrane (Fig. 7). The space between these two membranes is called the intermembrane space, and the space enclosed by the inner envelope membrane is called the stroma. In addition, chloroplasts have another membrane system within the stroma the thylakoid membrane forms the lumen. Therefore, there are six different localization sites and, of course, multiple pathways to each site. Naturally, their sorting mechanisms are very complicated. 

Mn was first shown to play an important role in photosynthetic 0 evolution by nutritional studies of algae (7). The stoichiometry of Mn in photosystem II was determined by quantitating Mn released from thylakoid membranes by various treatments (8). These experiments established that Mn is specifically required for water oxidation and that four Mn ions per photosystem II are required for optimal rates of 0 evolution (9). More recently, photosystem II preparations with high rates of Oj evolution have been isolated from a variety of sources (for a review see 10). The isolation of an O2-evolving photosystem II has proved to be a major step forward in both the biochemical and spectroscopic characterization of the O2-evolving system. These preparations contain four Mn ions per photosystem II (11), thus confirming that four Mn ions are functionally associated with each O2-evolving center. 

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