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| Author(s): |
Bertha Dévora Agurto Berdejo
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2010-03-11 |
| Examining board members: |
Ricardo Antunes de Azevedo;
Gerhard Bandel;
Renato Rodrigues Ferreira;
Leonardo Oliveira Medici;
Marcio José da Silva
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| Advisor: | Ricardo Antunes de Azevedo |
| Abstract | |
Maize which is the staple food in many countries in Africa, Asia and Latin America, has ~10% of protein in the seeds. Maize seeds protein presents low contents of essential amino acids, such as lysine and tryptophan. Since the discovery of the opaque-2 maize, a recessive mutation that results in high concentrations of lysine and tryptophan, the major challenge has been to develop better quality protein maize to increase the rate of amino acids consumed by population. The QPM (quality protein maize), originally produced and breeded at CIMMYT in Mexico, came to solve the issue. The QPM protein has twice as much lysine and tryptophan, with the same yield of normal maize. The EMBRAPA, Maize and Sorghum, has bred two QPM varieties that are already commercialized (BR 451 and BR 473), but to increase the quality of the Brazilian QPM, EMBRAPA developed a new QPM line, the 161, whose storage proteins were biochemically analyzed in this study. Line 161 exhibited a higher lysine concentration than BR 451, but about the same concentration of that exhibited by BR 473. Further analyses conducted in this research involved the study of immature seeds (14, 20 and 24 DAP) of line 161, and the wild-type W22+ and its counterpart mutants W22o10, W22o11 and W22o13, and the characterization of the enzyme homoserine kinase (HK). HK is a key enzyme of the threonine biosynthetic pathway. The high HK activity was shown to be related to the increased threonine concentration in the maize seeds. HK activity was shown to reach the highest level in the first developmental stage, whereas in the last developmental stage the activity is lower and so is the rate of threonine. Therefore, it is necessary more studies on HK regulation to improve the mature maize seeds with the best rate of lysine and threonine. (AU) | |