Plant cell organelles

Starch is stored in plant cells in the form of granules in the stroma of plas-tids (plant cell organelles) of two types chloroplasts, in which photosynthesis takes place, and amyloplasts, plastids that are specialized starch accumulation bodies. When starch is to be mobilized and used by the plant that stored it, it must be broken down into its component monosaccharides. Starch is split into its monosaccharide elements by stepwise phosphorolytic cleavage of glucose units, a reaction catalyzed by starch phosphorylase (Figure 7.23). This is formally an a(1 4)-glucan phosphorylase reaction, and at each step, the prod-... 

Structure of Cellular Membranes Plant Cell Organelles ... 

PLANT CELL ORGANELLES STRUCTURE-FUNCTION RELATIONSHIPS... 

One striking advance in modem subcellular biology is a more complete understanding of the interrelationship of certain plant cell organelles (Fig. 2A-F). Rather than existing as discrete entities in physiological and biochemical isolation of one another, it is now generally accepted... 

Halliwell B. Marker enzymes of plant cell organelles, in Methodological Developments in Biochemistry. 4. Subcellular Studies (Reid E, ed.), Longman, London, pp. 357-366. 

Photosynthesis occurs in the plant cell organelle called the chloroplast. During the process of photosynthesis, electrons are transferred from H20 to NADP+ via an electron carrier system. The energy released by electron transport is converted into the form of a proton gradient and coupled to ADP phosphorylation. In this experiment a method is introduced to demonstrate the formation of the proton gradient across the chloroplast membranes. 

Initially plant cell culture techniques progressed more slowly than those for animal cells, as did procedures for the isolation of plant cell organelles. Technical difficulties have now largely been overcome and culturing plant embryos has now found important commercial applications. 

Several observations concerning the lipids of plant cell organelles have suggested that lipid exchange can occur between the different membranes of plant cells. (1) Numerous analyses of cell membranes have been realized since refined chromatographic techniques were first developed, and all results have pointed out a real uniformity in the phospholipid and fatty acid contents of all cell membranes, within the same species, except for chloro-plast membranes (Mazliak et al., 1975 Mazliak, 1977). (2) Membrane lipids were proved to turn over continuously in cell organelles with half-lives varying from 3 days in microsomes to 10 days in mitochondria (Mazliak et al., 1968 Ben Abdelkader and Mazliak, 1971). However, carefully purified mito-... 

To determine which organelles were involved in lipid synthesis, plant cell organelles (mitochondria, microsomes, peroxisomes, plasmalemma, nuclei) were isolated in vitro and fed with various radioactive precursors ([ C]ace-tate or [ C]acetyl-CoA, [ K ]malonate or [ K ]malonyl-CoA, [ P]phos-phate, [ C]glycerol or [ K]l]glycerophosphate, [ C]choline or [ CJethanola-mine, etc.). The biosynthetic capacities of each organelle were thus evidenced (see Mazliak, 1975, 1977) in an effort to locate the sites of lipid synthesis in plant cells. The following points appeared clearly from the experiments ... 

The higher plant cell contains numerous distinct organelles or membra-nes, but only some of these have been properly purified and characterized. Determination of the jji vivo glycerollpld composition of these plant cell organelles or membranes, and their role In lipid metabolism Is not simple. In contrast to what Is often believed. 

The purpose of this article Is to summarize results obtained In our laboratory on plant cell organelles or membranes that we are able to prepare In highly purified and metabollcally competent forms. The methods we have developed allowed a better understanding of the specific properties and composition of each membrane system within the plant cell. 

GENERAL CONSIDERATIONS FOR THE ISOLATION OF PLANT CELL ORGANELLES... 

Glyaerolipid oompoaition of plant cell organelles from various plants... 

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