The role of lichenized algae in the production of Cladonia verticillaris depsidones, revealed by using alginate-immobilized cells

The mycobiont of the lichen Cladonia verticillaris produces two depsidones, protocetraric and fumarprotocetraric acids, in the nature. This last compound is produced from the former depsidone. To study the role of the algal partner in the production of these depsidones in the lichen thallus, fungal and algal partners were separated and immobilized in calcium alginate. The fungal immobilizates, as lichenized or isolated mycobiont, produced both depsidones, preferently fumarporotocetraric acid from acetate as a precursor. However, when algal immobilizates were co-incubated on acetate with the fungal ones, protocetraric acid was over-produced during the first 11 days of incubation to be later converted into fumarprotocetraric acid. We hypothesized about the algal production of a diffusible metabolite that inhibits the transformation of a depsidone into the other one

La ciencia de las plantas aprendida en jardines, casas, patios y azoteas

La ciencia impregna prácticamente todos los aspectos de nuestra vida gracias a la rapidez con la que se genera el conocimiento científico, la velocidad con la que dicho conocimiento se transmite y la profunda tecnificación de nuestra vida cotidiana. Velocidad que muchas veces no permite ese instante de reflexión que es necesario para que el concepto se comprenda correctamente y se incorpore al acervo cultural de nuestra persona. En este trabajo se analizan las fuentes de información, su credibilidad y la disponibilidad de fuentes de conocimiento que nuestra vida diaria pone a nuestra disposición en relación con la ciencia de las plantas

Effects of concanavalin A on the germination of smut teliospores and on the hyphal growth

Sporisorium scitamineum cells, that causes smut disease in sugar cane, respond to Concanavalin A (ConA). This lectin stimulates the cytoagglutination of teliospores, an excessive elongation of germinative tubes and induces morphological changes in hyphae, in the same way that it occurs in other cellular types. These events seem to play a defensive role in plants against pathogenic infections. In fact, ConA prevents S. scitamineum germination. Binding assays reveal that the distribution of ConA specific receptors is heterogeneous in both location and stage of cycle. Generally, it seems that the lectin activates mitotic events during the life cycle of cells that have been previously able to germinate. For example, increased cell budding is observed in released sporidia after contact with high concentration of the lectin. Moreover, desorption assays indicate that bound ConA is partially desorbed by methyl-mannose and by sugar cane glycoproteins, suggesting that important polysaccharide ligands involved in the defensive response against smut disease could be contained in sugar cane juice produced by resistant varieties

An elicitor isolated from smut teliospores (Sporisorium scitamineum) enhances lignin deposition on the cell wall on both sclerenchyma and xylem in sugarcane leaves

Sugarcane leaf shows the classical arrangement of cells which defines a C4 species. Vascular bundles consist of xylem, phloem and fibres, surrounded by an outer layer of sclereids and an inner ring of stone cells associated with the phloem. Some sclereids located below and above the vascular bundles act as docking cells and connect the vascular bundle to the internal surfaces of upper and lower layers of the epidermis. A compact mass of sclereids occupies the total internal volume of the leaf edge. Neither docking cells nor the internal mass of sclereids in the edge were markedly coloured by acriflavin or phloroglucinol, indicating the absence of lignin in their cell walls. However, such staining indicated that fibres of the vascular bundle and the external layer of sclereids were strongly lignified. Incubation of leaf discs with an elicitor produced by the pathogen Sporisorium scitamineum increased the thickness of the lignified cell walls of sclereids as well as the mid and small xylem vessels, as a possible mechanical defense response to the potential entry of the pathogen

Physiological basis of smut infectivity in the early stages of sugar cane colonization

Sugar cane smut (Sporisorium scitamineum) interactions have been traditionally considered from the plant’s point of view: How can resistant sugar cane plants defend themselves against smut disease? Resistant plants induce several defensive mechanisms that oppose fungal attacks. Herein, an overall view of Sporisorium scitamineum’s mechanisms of infection and the defense mechanisms of plants are presented. Quorum sensing effects and a continuous reorganization of cytoskeletal components, where actin, myosin, and microtubules are required to work together, seem to be some of the keys to a successful attack

Algal-fungal mutualism: cell recognition and maintenance of the symbiotic status of lichens

Lichens are specific symbiotic associations between photosynthetic algae or cyanobacteria and heterotrophic fungi forming a double entity in which both components coexist. Specificity required for the lichen establishment can be defined in this context as the preferential, but not exclusive, association of a biont with another, since the algal factor susceptible to be recognized is an inducible protein. Recognition of compatible algal cells is performed by specific lectins produced and secreted by the potential mycobiont. Some lectins from phycolichens and cyanolichens are glycosylated arginases which bind to an algal cell wall receptor, identified as a a-1, 4-polygalactosylated urease. However, other ligands exist which bind other lectins specific for mannose or glucose. This implies that, after recognition of a potential, compatible partner, other fungal lectins could determine the final success of the association. Since the fungus can parasitize non - recognized partners during the development of the association, the success after the first contact needs of a set of algal cells, the number of which was sufficient to prevent that the death of a certain number of them makes fail the symbiosis. Fungal lectins act as chemo tactic factors in such a way that algae and cyanobacteria move towards the hyphae, to acquire that critical size of the colony, by means of successive contractions and relaxation of the actomyosin cytoskeleton in absence of any motile appendages

Production of bioactive lichen compounds by alginate-immobilized bionts isolated from Cladonia verticillaris: an in vitro study

Bionts isolated from thalli of Cladonia verticillaris, immobilized in calcium alginate, produce two depsidones, fumarprotocetraric and protocetraric acids, and the depside atranorin, that exhibit antimicrobial activity against Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae. Organic lichen extract (acetone/ether/chloroform) shows the highest antimicrobial activity due to a possible synergism between these substances. Antioxidant capacity of soluble metabolites secreted from the immobilisates to the bath medium of incubation during the first 12 days of immobilization has been found (˃80% oxidation inhibition). The concentration of soluble phenolic substances depends on the immobilization time (during 32 days), exogenous supply of acetate (1.0m mM sodium or calcium acetate) and on the type of isolated biont (phycobionts, mycobionts, whole thallus or immobilized phycobionts co-incubated with the mycobionts ones). The role of phycobionts in phenol production has been interpreted as a possible modification of the polymalonyl pathway; for example, atranorin is actively produced and secreted during immobilization while it is not detected in thallus in natura. Co-incubated bionts secrete higher amounts of atranorin to the media during the first 12 days of immobilization. Immobilization of isolated bionts could be used as a biotechnological technique to obtain a potential source of biological active compounds. On the other hand, the physiological state detected of C. verticillaris in the Cerrado is much better for experimentation than that of the specimens collected in Caatinga since, in this case, the thalli showed the fragility that the extreme environmental conditions of the semi-arid region of NE Brazil impose on this lichen species. To date, no priority has been defined for lichen conservation in Brazilian ecosystems. It is therefore suggested that it imust important to include lichen ecophysiology studies in public conservation policies

Biologically-active compounds from Brazilian lichens and their affinity with ether

It can be obtained from lichens biologically-active extracts and pure substances, many of them of phenolic nature. They are usually obtained by using organic solvents, such as diethyl ether. In this paper the usefulness of ether for the obtainment of crude extracts and the subsequent purification of pure substances from Brazilian lichen is reviewed, as well as alternatives to their production through cells or thallus immobilization in bioreactors and their entrapment in inert matrix

Xanthan production by Xanthomonas albilineans infecting sugarcane stalks

Xanthomonas albilineans is the causal organism of leaf scald, a bacterial vascular disease of sugarcane. Xanthomonas may invade the parenchyma between the bundles and cause reddened pockets of gum, identified as a xanthan-like polysaccharide. Since xanthan contains glucuronic acid, the ability of Xanthomonas to produce an active UDP glucose dehydrogenase is often seen as a virulence factor. X. albilineans axenically cultured did not secrete xanthans to Willbrink liquid media, but the use of inoculated sugarcane tissues for producing and characterizing xanthans has been required. A hypothesis about the role of sugarcane polysaccharides to assure the production of bacterial xanthan is discussed.Depto. de Farmacia Galénica y Tecnología AlimentariaFac. de VeterinariaTRUEpu