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| Author(s): |
Reinaldo Montrazi Barata
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 1999-07-02 |
| Advisor: | Marcio de Castro Silva Filho |
| Abstract | |
Oxygen is essential for respiration and also participates in the primary and secondary metabolism of plant cells. Severa! attempts have been made to alter the aerobic metabolism in plants, especially those related to the oxygenation or carboxylation of Rubisco (ribulose 1,5-bisphosphate carboxylase-oxygenase). However, designing a more effective Rubisco protein is rather problematic since its structural manipulation leads frequently to an enhancement of oxygenase activity, which is responsible for photorespiratory losses. ln order to reduce oxygen availability inside chloroplasts a chimeric gene, consisting of a soybean leghemoglobin cDNA (Iba) bound to the chloroplast targeting signal sequence of the Rubisco small subunit gene was introduced and expressed in Nicotiana tabacum. Leghemoglobin was efficiently imported and correctly processed inside the chloroplasts in transgenic tobacco plants. Furthermore, the maximum level of Lba expression in leaf tissue ranged from 0,01 a 0,1%. Analysis of photosynthesis, metabolite production (sucrose and starch) and enzymes involved in aerobic metabolism in plants cells (catalase [CAT], glutathione reductase [GR] and superoxide dismutase [SOD]) revealed that despite of high affinity of leghemoglobin to oxygen, no difference was observed in relation to contrai plants. These results suggest that higher Lba concentrations must be present inside the organelle in arder to act as an oxygen carrier or facilitate diffusion. (AU) | |