[Recent advances in the study of Vitreoscilla hemoglobin(VHb) and related proteins - cloning, expression and physiological actions in heterologons hosts and in transgenic tobacco plants].

The first bacterial hemoglobin(VHb) was found in a strictly aerobic bacterium, Vitreoscilla strain C1, occurring in marshes low in oxygen, but rich in organic matter. The hemoglobin gene is induced under low oxygen tension and may amount to 20 times as high. The expression of VHb promotes cell growth, protein biosynthesis and primary and secondary metabolism of the host cells, because the increased intracellular oxygen accelerates both the function of respiratory chain and terminal oxidases. The serial action of increased oxygen concentration is elucidated through yeast two hybrid system and a model is proposed. In addition, novel globin proteins known as flavohemoglobins have been isolated from various procaryotes and eucaryotes, with a N-terminal similar to VHb and C-terminal with reductase activity. Primary study shows that flavohemoglobin proteins exhibit similar function as VHb and also protection effect to nitrosative stress. Further work is needed to learn more about the physiology of these flavohemoglobins. The most remarkable physiological effects of VHb are exihibited in transgenic tobacco plants, including accelerated seed germination and growth in plant, increased synthesis of chlorophyll and dry weight. Without doubt, these effects are brought about through the increased oxygen supply to plant cells. It is deemed that VHb transgenic tobacco is a forerunner for transgenic crops and VHb may be a valuable route for staple seed crops.