Plastids interrelationships

Sapozhnikov, D.I., Kransovskaya, T.A., and Maevskaya, A.N. 1957. Change in the interrelationship of the basic carotenoids of the plastids of green leaves under the action of light. Dokl. Acad. Nauk USSR 113 465 167. 

The mevalonate-independent pathway is present in most bacteria and all phototropic organisms. In higher plants and most algae both pathways run independently. The mevalonate pathway is located in the cytoplasm and is responsible for the biosynthesis of most sesquiterpenoids. The mevalonate-independent pathway, in contrast, is restricted to the chloroplasts where plastid-related isoprenoids such as monoterpenes and diterpenes are biosynthesised via this pathway [43-45]. Figure 4.2 illustrates the interrelationships of both biosynthetic pathways connected to Fig. 4.1 [46]. 

Whatley, J. B. 1978. A suggested cycle of plastid development interrelationships. New Phytol. 80, 489-502. 

In photosynthetic tissues, or example, novo fatty acid synthesis is Localised in the chloroplast where the central cofactor/cosubstrate for carbon-8 to carbon-18 fatty acid synthesis is acyl carrier protein. There is some evidence that fatty acid chain length and fatty acid distribution within the different cellular organalles may be regulated by isoform structure of acyl carrier protein. In the developing oil seed, on the other hand, the most probable site of acyl carrier protein-mediated fatty acid synthesis is the plastid. The complex interrelationship between de novo fatty acid synthesis and the Kennedy pathway will need to be understood before genetic manipulation of the acyl carrier protein gene can be contemplated on a rational basis. 

Further research activities have included the partial characterization of the plant HMG-CoA reductase and the study of the interrelationship between the cytoplasmic and organelle me-valonate pathways. He has also showed that mitochondrial biomembranes of most plants simultaneously contain two or more homoiogues of ubiquinones as electron carriers. More recently his research has been concerned with the de novo fatty acid and lipid biosynthesis as affected by xenobiotics. Here Hartmut LIchtenthaier has presented evidence that the plastidic acetyl-CoA carboxylase is the target for various classes of new herbicides. 

Wien we leave photosynthesis we also leave the area in which it is easy to distinguish what each part of the cell does. As do all other organelles, the chloroplast lives in a complex environment which is controlled largely by the activity of the nucleus but to which the metabolic activities of the other organelles— including the mitochondria, the Golgi apparatus, etc., as well as the chloroplasts themselves— undoubtedly contribute. These interrelationships must be resolved before the control of plastid development will be understood. In the meantime, in order to be able to proceed with any sort of discussion, we must recall that one of the functions of the chloroplast appears to be its own maintenance. Here we must eventually come to the questions How independent is the chloroplast in maintaining itself How dependent is the plastid on activities of other portions of the cell or on information available within the nucleus in a particular species or strain ... 

Many characters that affect chloroplast development are known to be inherited in a Mendelian manner they are readily detected as aberrations in the normal greening pattern. On the other hand, it is well known that some plastid characters are inherited in a non-Mendelian manner (Rhoades, 1955 Granick, 1955). Thus, if we restrict ourselves to a few cases in which chloroplast development is controlled by nuclear genes, and in which the nature of the lesion occasioned by transmission of defective information is understood, we should see some examples of the interrelationship between the nuclear genome and chloroplast development. 

Fig. 2.15. The interrelationships of plastids. Only pro-plastids and mature chloroplasts are known to divide. (From F. A. L. Clowes and B. E. Juniper, Piawt CeUs, Blackwell Scientific Publications, Oxford, 1968.)...

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