Chloroplast transfer

Genetic techniques for obtaining chloroplast-encoded herbicide resistance in crop plants are reviewed. These are based on the use of cell culture methods and Include mutant selection in cultured cells, chloroplast transfer via protoplast fusion, and genetic recombination between chloroplast genomes. The first two methods are described in detail using trlazine resistance as an example. 

The chloroplasts of triazine-resistant weed species are a potential source of herbicide resistance for treinsfer into crop plants. Chloroplast transfer, that is the combination of desirable chloroplasts and nuclei, can be achieved by crossing or by protoplast fusion. Chloroplast transfer by crossing is carried out using the line with the desirable chloroplasts as the maternal parent and the line with the desirable nuclear background as the pollen parent. Repeated crossing results in substituting the chromosomes (nucleus) of the chloroplast source with those of the recurrent pollen parent as chloroplasts in crops are only inherited by the maternal parent. This strategy has been used to introduce the triazine-resistant chloroplasts from bird s rape (a weed, Brassica campestris) into cultivated B. campestris and B. napus... 

Protoplast fusion provides ein alternative method for chloroplast transfer (17,18). Transfer is based on the independent segregation of chloroplasts eind nuclei in heterokaryons obtained by protoplast fusion. Efficiency of recovery for specific combinations of chloroplasts and nuclei has been facilitated by using selectable chloroplast markers such as streptomycin or linoomyoin resistance, or by using maternal pigment-deficient mutants to visually differentiate between clones carrying donor and recipient chloroplasts. Elimination of the nucleus of the chloroplast donor is facilitated by irradiation of donor protoplasts prior to fusion. Methods of chloroplast transfer by protoplast fusion have been reviewed (17,18). In this review only transfer of triazine-resistant chloroplasts will be covered. Work in Nicotiana is more recent than in rapeseed ( 9) and potato (, 1 ), but serves to Illustrate the methodology of chloroplast transfer by protoplast fusion. 

Chloroplast transfer into potato. Transfer of atrazine-resistant planum nigrum chloroplasts into S. tuberosum has been attempted by protoplast fusion (20,21 ). In the absence of irradiating the chloroplast donor S. nigrum, only somatic hybrids were obtained... 

Acyl-(acyl-carrier protein) glycerol-3-phosphate acyl transferase (glycero-P acyltransferasc) in higher-plant chloroplasts transfers the acyl group from acyl-(acyl-carrier protein) to the C-1 position of glycerol 3-phosphate to synthesize 1-acylglycerol 3-phosphate. Since this reaction is the first step of glycerolipid synthesis in the chloroplasts, it is of special interest to study this enzyme. 

Assuming that the concentrations of ATP, ADP, and P in chloroplasts are 3 mM, 0.1 mM, and 10 mM, respectively, what is the AG for ATP synthesis under these conditions Photosynthetic electron transport establishes the proton-motive force driving photophosphorylation. What redox potential difference is necessary to achieve ATP synthesis under the foregoing conditions, assuming an electron pair is transferred per molecule of ATP generated ... 

Both the intracellular and the plasma membranes are actively involved in the cell s vital functions. In the surface membranes of axons, processes of information transfer in the form of electrical signals (nerve impulses) lake place. Bioenergy conversion processes occur at the intracellular membranes of the mitochondria and chloroplasts. 

It has been suggested that trapping of this delocalized excitation by low-energy impurity molecules could play an important role in the photophysics of chloroplasts. After trapping the excitation energy, it could be transferred to a reactant or an electron transfer reaction could occur/351... 

Fig. 10.11 The modified tree of life still has the usual tree-like structure and also confirms that the eukaryotes originally took over mitochondria and chloroplasts from bacteria. It does, however, also show a network of links between the branches. The many interconnections indicate a frequent transfer of genes between unicellular organisms. The modified tree of life is not derived, as had previously been assumed, from a single cell (the hypothetical primeval cell ). Instead, the three main kingdoms are more likely to have developed from a community of primitive cells with different genomes (Doolittle, 2000)...

Chlorella zofingensis cells are transferred to a growth medium, with a low nitrogen concentration (10% of normal concentration). After approximately 6-8 wk they develop a red colour, due to the decomposition of chlorophylls and synthesis of secondary carotenoids (stored in lipid droplets within the cytoplasm of the cells). At this stage the chloroplast are intact, although the surface area of thylacoids is mostly reduced. 

In plants, the photosynthesis reaction takes place in specialized organelles termed chloroplasts. The chloroplasts are bounded in a two-membrane envelope with an additional third internal membrane called thylakoid membrane. This thylakoid membrane is a highly folded structure, which encloses a distinct compartment called thylakoid lumen. The chlorophyll found in chloroplasts is bound to the protein in the thylakoid membrane. The major photosensitive molecules in plants are the chlorophylls chlorophyll a and chlorophyll b. They are coupled through electron transfer chains to other molecules that act as electron carriers. Structures of chlorophyll a, chlorophyll b, and pheophytin a are shown in Figure 7.9. 

The integration of PS I and PS II in chloroplasts occurs as shown in Figure 7.10 [37,39]. The overall reaction of the transfer of electrons starting from water takes place in three stages. 

---