Kelly Simões

Purification and characterization of a phytoalexin elicitor from spores of the saprobe Mucor ramosissimus

Plantas acumulam compostos antimicrobianos (fitoalexinas) em resposta a uma grande variedade de microorganismos. Mucor ramosissimus Samutsevitsch e um fungo saprobio capaz de induzir a producao de fitoalexinas em soja e em Rubiaceae nativas, sobre a superficie das quais ele e encontrado. Neste estudo, o eliciador de esporos de M. ramosissimus foi parcialmente purificado e sua atividade comparada ao glucano isolado de Phytophthora sojae. O otimo de isolamento do eliciador (baseado no crescimento do fungo, no rendimento dos esporos e na atividade eliciadora) foi obtido a partir de esporos autoclavados de culturas do fungo com nove dias de idade. O eliciador foi precipitado com etanol e purificado por cromatografia de troca ionica, a qual reteve o eliciador, e por uma matriz de afinidade em Concanavalina-A, a qual o eliciador nao se ligou. A purificacao resultou em consideravel aumento (seis vezes) de atividade especifica do eliciador. Analises de acucares neutros por HPLC revelaram a predominância de manose, seguida de glucose e galactose, enquanto que a quantificacao por colorimetria mostrou a presenca de acidos uronicos. Analises do eliciador por GC-MS indicaram a predominância de acido glucuronico e manose. Esses resultados sugerem que fragmentos de um polissacarideo do tipo mucorano sao os eliciadores de fitoalexinas presentes nos esporos de M. ramosissimus. Os resultados tambem indicam, pela primeira vez, que os tecidos de cotiledones de soja reconhecem fragmentos de heteropolimeros de acidos uronicos como eliciadores de fitoalexinas.

Potential allelopathic effects of the tropical legume Sesbania virgata on the alien Leucaena leucocephala related to seed carbohydrate metabolism

Allelopathy has been considered a key mechanism to explain the invasiveness of some species. It is well known that invasive plants can affect native plants by producing novel allelochemicals but some exotic plant species may be also sensitive to allelochemicals released by native species, providing a tool to reduce growth and impacts of invasive exotic species. Here, using growth chamber experiments we tested the mutual potential allelopathic effects of Sesbania virgata (a native dominant species) and the alien Leucaena leucocephala seeds. S. virgata was unaffected by seed leachates of L. leucocephala, indicating that, under lab conditions, this legume presents resistance to the phytotoxic compounds produced by seeds of this alien species. In contrast, germination and seedling growth of L. leucocephala were strongly affected by the phytochemicals produced by seeds of S. virgata. A delay in endospermic mobilization of storage carbohydrates (raffinose-family oligosaccharides and galactomannan) was observed in the alien species. These potential allelopathic effects could not be attributed sole to the presence neither of the phytoxic catechin nor of ABA in seed leachates of S. virgata. Our findings indicate that the in vitro behavior of S. virgata is consistent with its aggressiveness in natural environment and suggest sesbanimide as a potential candidate as implicated in the noxious effects of S. virgata on the alien species.

Phytotoxic effect of Sesbania virgata (Cav.) Pers. on seeds of agronomic and forestry species

Sesbania virgata (Cav.) Pers. is a pioneer species native to South America able to release allelochemicals that affect germination and development of other plant species. The aim of this work was to evaluate the allelopathic effect of S. virgata on the germination and development of co-occurring species from gallery forest and on agronomic species. Two forest native species, Enterolobium contortisiliquum (Vell.) Morong and Sapindus saponaria L., and two agronomic species (these as control), Oryza sativa L. and Solanum lycopersicum L. were used in the lab and greenhouse assays with seeds and leaf extracts of S. virgata. Agronomic species were more affected than native species when co-germinated with seeds of S. virgata. The germination percentage and speed germination index of the agronomic species were reduced in both in vitro and greenhouse assays. In the same assays, the seeds of native species showed no significant differences in the parameters mentioned. However, the initial growth of the four species assayed was affected, with reduction in plant length and shoot diameter followed by significant reduction in plantlet shoot and root weights. In the assays with irrigation of S. virgata leaf extracts, no significant inhibitory effects on germination were observed for all species. Height and shoot diameter of the native species were not affected by the leaf extracts, nor were fresh and dry weights. However, these parameters increased in the agronomic species as they were irrigated with leaf extracts. Based on our data we conclude that seed leachates of S. virgata affect germination and seedling development of other species, suggesting that its invasive behavior is due mainly to seed allelochemicals. Although with less pronounced effects on native species, allelopathy of S. virgata might also influence Interspecific competition in its natural environment.

Substâncias antifúngicas constitutivas e induzidas em folhas e suspensões celulares de Rudgea jasminoides (Cham.) Müll. Arg. (Rubiaceae)

Rudgea jasminoides (Cham.) Mull. Arg. is a woody Rubiaceae species from tropical forest that synthesized antifungal secondary metabolites when challenged by fungi. Members of the Rubiaceae are among the few plants that are easily taken into cell cultures to produce substantial amounts of secondary products that surpass those of the whole plant. In this work we analyzed the presence of constitutive and induced antifungal compounds produced by leaves and cell suspension cultures of this species. Oligogalacturonides (OGAs), salicylic acid (AS), nitric oxide (NO), and yeast β-glucan fragments were used as elicitors. Constitutive compounds with antifungal activity were detected in cell suspension cultures of R. jasminoides, mainly during the stationary growth phase. They were found in higher diversity and amounts than those present in leaves. Treatment with β-glucan fragments increased the production of constitutive compounds and induced the synthesis of antifungal metabolites absent in non-elicited cultures (phytoalexins), mainly during the exponential growth phase. OGAs derived from R. jasminoides leaf cell walls showed similar effect. Under our experimental conditions, the endogenous signaling molecules salicylic acid and nitric oxide were toxic to the cells and did not act as elicitors of antifungal compounds in suspension cultures of R. jasminoides. Our data indicate that cell suspension cultures of R. jasminoides are able to synthesize antifungal compounds and their production can be enhanced by fungal or plant elicitors.

Carbohydrate mobilisation in germinating seed of Enterolobium contortisiliquum and Peltophorum dubium (Fabaceae), two tropical trees used for restoration

Enterolobium contortisiliquum (Vell.) Morong. and Peltophorum dubium (Spreng.) are two leguminous species native to Brazil that are frequently used to restore degraded areas. Seed of E. contortisiliquum are exalbuminous, whereas seed of P. dubium have a mucilaginous endosperm and both are orthodox, dormant and have a water-impermeable seed coat. There is little information about the dynamics of their germination and understanding this process is important for propagation, conservation and satisfactory practices for restoration of degraded areas. Thus, in this study we evaluated and compared the carbohydrate mobilisation of the seed of both species during germination and early seedling development. Data obtained showed differences in the composition and in the mobilisation of the storage carbohydrates in the studied species. Whereas the main storage of the E. contortisiliquum embryo is starch, the main reserve found in P. dubium is the galactomannan stored in the endosperm. The carbohydrates first hydrolysed in both species are raffinose family oligosaccharides that are used in the embryo development during germination. Starch found in cotyledons of E. contortisiliquum or accumulated after galactomannan degradation in the embryo of P. dubium is not used during germination and early seedling growth in either species.