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Plant cells are compartmentalized into organelles enveloped by membranes impermeable to coenzyme A or its derivative Acyl-CoA. Coenzyme A is involved in anabolic and catabolic pathways at various compartments of the plant cell (Somerville et al., 2000). Thus, there may be multiple plant coenzyme A biosynthetic pathways in different sub-cellular compartments, unlike in yeast and bacteria. Plant pantothenate synthetase identified by Genschel, et al. (1999) lacked a signal sequence that targets it to chloroplast or mitochondria. Besides, contrary to the characteristic strong similarity of chloroplastic proteins with cynobacteria proteins, the Lotus and rice pantothenate synthetase showed greater similarity with pantothenate synthetase (panC) from E.coli than cynobacterium Synechosystis. They inferred that the Lotus and rice pantothenate synthetase is cytosolic. Earlier work on spinach by Falk and Guerra (1993) and Julliard (1994), however, indicated presence of pantothenate biosynthesis in chloroplast to which pantoyl-lactone is the substrate instead of pantoate.
Several biosynthetic pathways in the various plant sub-cellular compartments use coenzyme A or Acetyl-CoA. Acetyl-CoA in the plastid is precursor for fatty acid synthesis whereas in the cytosol it is substrate for fatty acid elongation and desaturation, lignin, isoprenoids and flavonoid synthesis. In mitochondria and peroxisome/glyoxisome, it is a substrate in the energy yielding process of TCA cycle and storage lipid catabolism, respectively. Coenzyme A activity in the various sub-cellular compartments is likely to be well coordinated in response to the plant developmental and growing condition changes (Podkowinski et al., 2003).
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Last Updated on Monday, 12 October 2009 |
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