Targeting of the soybean leghemoglobin to tobacco chloroplasts: effects on aerobic metabolism in transgenic plants.
Several attempts have been made to alter the aerobic metabolism of plants, especially those related to the oxygenation or carboxylation of Rubisco. However, designing a more efficient Rubisco protein is rather problematic since its structural manipulation leads frequently to an enhancement of oxygenase activity, which is responsible for photorespiratory losses. In order to reduce oxygen availability inside the chloroplast, a chimeric gene consisting of a soybean leghemoglobin cDNA (lba) ligated to the chloroplast targeting signal sequence of the Rubisco small subunit gene, was introduced and expressed in Nicotiana tabacum. Lb was efficiently imported and correctly processed inside the chloroplasts of transgenic tobacco plants. Furthermore, the level of Lb expression in leaf tissue ranged from 0.01 to 0.1%. Analysis of photosynthesis, starch, sucrose and enzymes involved in aerobic metabolism, revealed that despite the high affinity of Lb for oxygen, no significant difference was observed in relation to the control plants. These results suggest that higher Lb concentrations would be required inside the chloroplasts in order to interfere on aerobic metabolism.
Barata
RM
Departamento de Genética, Escola Superior de Agricultura 'Luiz de Queiroz', Universidade de São Paulo, Av. Pádua Dias, 11, Caixa Postal 83, 13400-970, Piracicaba, SP, Brazil
Chaparro
A
Chabregas
SM
González
R
Labate
CA
Azevedo
RA
Sarath
G
Lea
PJ
Silva-Filho
MC