Biochemical and Physiological Characterization of Nonsymbiotic Plant Hemoglobins

University dissertation from Lund University

Abstract: Hemoglobins (Hb) are usually associated with blood in humans. However, these proteins are widely distributed among living organisms. In plants the most known group are the leghemoglobins. Still, other Hbs that not participate in symbiosis are also found. They are known as nonsymbiotic Hbs (nsHbs). NsHbs are divided into class-1 and class-2. In this thesis three nsHbs from sugar beet (BvHb1-1, BvHb1-2, and BvHb2) and one class-1 nsHb from poplar (PttHb1) have been studied. Additionally, the possibility of using nsHbs for biotechnological application is explored. A holistic expression study of the three BvHbs was done. Following the recombinant production of the three BvHbs, their kinetics and binding affinities to oxygen and CO were determined. Concerning PttHb1, its role as a NO scavenger was investigated by expressing it in roots and mutant yeast. We conclude that, even though differential roles have been given to both class-1 and class-2 nsHbs, a specific function can not be given to each group. On the contrary we found that for some nsHbs their roles may be complementary and overlapping. However, some class-1 nsHbs seem to have a clear NO dioxygenase function. In this study we demonstrate that PttHb1 alleviates NO toxicity in cells when expressed together with PtthFNR, a reductase. To finalize, given that nsHbs have a variety of potential roles, the possibility of being interesting biotechnological targets is studied. Early results regarding the expression of class-2 nsHbs in the model plant A. thaliana and in a potential crop Lepidium campestre are presented.