Phytomonas spp: superoxide dismutase in plant trypanosomes.

In 1909, Donovan [1] proposed the creation of a new genus, Phytomonas, to differentiate plant from animal trypanosomatids. Phytomonas spp. live in the latex, sap, sieve tubes, and fruit of many plant species [2]. At first, considerable controversy surrounded the pathogenicity of phytomonads in plants, as initially these parasitic protozoans were not thought to be particularly harmful. However, evidence from a number of plants of great economic significance, such as coffee, coconut, and palm, has shown that Phytomonas infections can have devastating economic consequences [3]. The defence mechanisms of trypanosomatids against the toxic products of O2 reduction – e.g. superoxide anion, hydrogen peroxide or hydroxyl radicals – are not completely understood. Trypanosomatids are protected from the damaging effects of reactive oxygen intermediates by scavengers such as trypanothione and specific enzymes such as superoxide dismutase (SOD, EC 1.15.1.1) and trypanothione peroxidase. Catalase, involved in the elimination of hydrogen peroxide, is absent from most trypanosomatids, although it has been detected in Crithidia luciliae [4] and in Phytomonas spp. [5]. Cyanide-insensitive SOD activity has been reported in Trypanosoma cruzi [6], as well as in other trypanosomatids such as Crithidia fasciculata [7] and Trypanosoma brucei [4]. The SOD activities of Leishmania tropica and T. cruzi are also cyanide-insensitive but peroxide-sensitive [7]. SOD of C. fasciculata is located in the cytosol and exists in three forms, which may represent three distinct isozymes. Comparisons of the amino-acid sequence of this SOD with those of SODs from other sources suggest that the crithidial enzyme is closely related to bacterial FeSOD of the alga Euglena gracilis. SOD activity has also been detected in L. dono ani and Phytomonas spp., although its nature has not been determined [8,9]. Most of the information on the biochemistry of plant flagellates has come from experiments in which the flagellates were used as instruments in biochemical research rather than from studies investigating the biochemistry of the plant flagellates themselves. Probably for this reason, these studies are scattered through a variety of subjects, and, despite the amount of information gathered in recent years, our knowledge of the biochemistry of Phytomonas remains fragmentary [3]. In this sense, the detoxifying mechanisms of oxygen radicals in plant trypanosomatids are unknown. From previous studies [10], we know that plant flagellates have SOD activity, but we have yet to identify the role of this enzyme in the destruction of the superoxide radicals, and there is no information available on the enzyme itself. In the present work, we confirm and quantify the SOD activity in three trypanosomes isolated from different plants: from phloem of the Coco nucifera (Hartrot disease) [11], from latex vessels of Euphorbia characias [12], from the fruits of Lycopersicon esculenAbbre iations: Cu/ZnSOD, copper/zinc-containing superoxide dismutase; FeSOD, iron-containing superoxide dismutase; ME, malic enzyme; MnSOD, manganese-containing superoxide dismutase; NBT, nitro-blue tetrazolium salt; PK, pyruvate kinase; PFK, 6-phospho fructose kinase; SOD, superoxide dismutase. * Corresponding author. Tel.: +34-958-242369; fax: +34-958243174. E-mail address: [email protected] (M. Sánchez-Moreno).