Marcia R. Braga

Elevated CO2 atmosphere promotes plant growth and inulin production in the cerrado species Vernonia herbacea

Carbon allocation in biomass is an important response of plants to the increasing atmospheric [CO2]. The effects of elevated [CO2] are scarcely reported in fructan-accumulating plants and even less in tropical wild species storing this type of carbohydrate. In the present study, the effects of high [CO2] atmosphere was evaluated on growth, biomass allocation and fructan metabolism in Vernonia herbacea (Vell.) Rusby, an Asteraceae from the Brazilian cerrado, which accumulates inulin-type fructans in the underground organs (rhizophores). Plants were cultivated for 120 days in open-top chambers (OTCs) under ambient (~380 μmol mol–1), and elevated (~760 μmol mol–1) [CO2]. Plant growth, photosynthesis, fructan contents, and the activities of fructan metabolising enzymes were analysed in the rhizophores at Time 0 and 15, 30, 60, 90 and 120 days. Plants under elevated [CO2] presented increases in height (40%), photosynthesis (63%) and biomass of aerial (32%) and underground (47%) organs when compared with control plants. Under elevated [CO2] plants also presented higher 1-SST, 1-FFT and invertase activities and lower 1-FEH activity. Although fructan concentration remained unchanged, fructan productivity was higher in plants maintained under elevated [CO2], due to their higher rhizophore biomass. This is the first report on the effects of elevated [CO2] on a plant species bearing underground organs that accumulate fructans. Our results indicate that plants of V. herbacea can benefit from elevated atmospheric [CO2] by increasing growth and carbon allocation for the production of inulin, and may contribute to predict a future scenario for the impact of this atmospheric condition on the herbaceous vegetation of the cerrado.

Mitochondrial Nitric Oxide Synthesis During Plant–Pathogen Interactions: Role of Nitrate Reductase in Providing Substrates

Nitric oxide (. NO) is an important signaling molecule that regulates plant metabolism and mediates defense responses against biotic and abiotic stresses. Although the cellular mechanisms by which .NO is generated in plants have been intensively investigated, they still remain controversial, particularly those implicated in plant resistance to pathogens. .NO can be synthesized in plants via the oxidation of l-arginine into l-citrulline by a nitric oxide synthase (NOS) that has no homology with the animal NOS family. In addition to l-arginine, nitrite is also an important source for .NO in plants. Since nitrate reductase (NR) activity is required for .NO production, reduction of nitrite catalyzed by the enzyme has been considered a major .NO source in plants. Recent experimental data, however, indicate that NR-defective mutant plants can synthesize .NO from exogenous nitrite. Nevertheless, NR-deficient plants lack enough endogenous substrates (l-arginine and nitrite) for adequate .NO synthesis, resulting in an impaired hypersensitive response (HR). These findings indicate that NR activity is an important source of substrates for .NO production. The main pathways for .NO production from l-arginine and nitrite in plants are located in mitochondria, suggesting that these organelles play a central role in .NO signaling.

Differential sugar uptake by cell suspension cultures of Rudgea jasminoides, a tropical woody Rubiaceae

The primary utilization of carbohydrates by cell suspension cultures of Rudgea jasminoides, a native woody Rubiaceae from tropical forests, was investigated. Sucrose, glucose + fructose, glucose, or fructose were supplied as carbon sources. The growth curves of R. jasminoides cultured in glucose + fructose, glucose, or fructose showed similar patterns to that observed when sucrose was supplied to the cells, except that an increase in dry mass was observed at the beginning of the stationary growth phase in the media containing only one monosaccharide. The increase in hexose levels in the media during the early stages of the cultures indicated extracellular hydrolysis of sucrose, which was further supported by the increase in the activity of acid invertase bound to the cell wall. Glucose was preferentially taken up, whereas uptake of fructose was delayed until glucose was nearly depleted from the medium. Measurements of intracellular sucrose content and cytoplasmatic and vacuolar invertases indicate that the enzymatic activity seems to be correlated with a decrease in the hexose flux into the cells of R. jasminoides. Our results indicate that the behavior of cell suspension cultures of R. jasminoides regarding sugar utilization seems to be similar to other dicotyledonous undifferentiated cell suspension cultures.

Woronin bodies in Penicillium janczewskii Zaleski

Penicillium janczewskii Zaleski is an efficient microorganism for the production of extracellular inulinases and grows rapidly on medium containing sucrose or inulin as carbon source. Maintenance of this filamentous fungus on inulin medium induces secretion of large amounts of inulinases, but the resulting mycelium has thinner cell walls that easily collapse and break. Woronin bodies in hyphae of P. janczewskii grown on sucrose and inulin substrates were observed. No significant differences in the number, location, size and shape of Woronin bodies and level of plugging were observed in cultures of the fungus grown on the two carbon sources. The data indicate that the presence of Woronin bodies in P. janczewskii could not be associated with more easily damaged hyphae, although the function of these organelles in pore plugging has been confirmed.