Joséli Schwambach

When stress and development go hand in hand: main hormonal controls of adventitious rooting in cuttings.

Adventitious rooting (AR) is a multifactorial response leading to new roots at the base of stem cuttings, and the establishment of a complete and autonomous plant. AR has two main phases: (a) induction, with a requirement for higher auxin concentration; (b) formation, inhibited by high auxin and in which anatomical changes take place. The first stages of this process in severed organs necessarily include wounding and water stress responses which may trigger hormonal changes that contribute to reprogram target cells that are competent to respond to rooting stimuli. At severance, the roles of jasmonate and abscisic acid are critical for wound response and perhaps sink strength establishment, although their negative roles on the cell cycle may inhibit root induction. Strigolactones may also inhibit AR. A reduced concentration of cytokinins in cuttings results from the separation of the root system, whose tips are a relevant source of these root induction inhibitors. The combined increased accumulation of basipetally transported auxins from the shoot apex at the cutting base is often sufficient for AR in easy-to-root species. The role of peroxidases and phenolic compounds in auxin catabolism may be critical at these early stages right after wounding. The events leading to AR strongly depend on mother plant nutritional status, both in terms of minerals and carbohydrates, as well as on sink establishment at cutting bases. Auxins play a central role in AR. Auxin transporters control auxin canalization to target cells. There, auxins act primarily through selective proteolysis and cell wall loosening, via their receptor proteins TIR1 (transport inhibitor response 1) and ABP1 (Auxin-Binding Protein 1). A complex microRNA circuitry is involved in the control of auxin response factors essential for gene expression in AR. After root establishment, new hormonal controls take place, with auxins being required at lower concentrations for root meristem maintenance and cytokinins needed for root tissue differentiation.

Pre and post-severance effects of light quality on carbohydrate dynamics and microcutting adventitious rooting of two Eucalyptus species of contrasting recalcitrance

Adventitious rooting is a complex developmental response affected by genetic and environmental factors. Radiation quality effects on adventitious rooting depend on characteristics such as species, growth stage, irradiance, spectral quality, and time of exposure. Eucalyptus is an essential genus for the paper industry, and high yield plantations depend on adventitious rooting of selected genotypes. This work addressed two hypotheses: (1) radiation quality equally affects adventitious rooting in Eucalyptus species of different recalcitrance; (2) adventitious rooting outcome depends on both donor plant and cutting radiation quality treatments. To that end, the easy-to-root Eucalyptus grandis and the recalcitrant Eucalyptus globulus were evaluated. The effect of white, blue, red and far-red radiation enrichment on microcuttings and donor plants of both species was evaluated in relation to rooting. There was no effect of radiation quality on adventitious rooting of E. grandis or when radiation treatments were applied to E. globulus microcuttings. In contrast, donor plants of E. globulus, grown in medium devoid of sucrose and exposed to far-red radiation, yielded microcuttings showing higher rooting percentage, even in the absence of exogenous auxin in the rooting medium. Sucrose in donor plant medium abolished the positive effect of far-red radiation. An increase in endogenous soluble sugars and starch contents in basal microcuttings was associated with far-red radiation treatment of donor plants. These results underline the importance of appropriate carbohydrate partitioning in donor plants for adventitious rooting of cuttings and provide a basis for understanding and overcoming rooting recalcitrance in E. globulus clones.

Genus Mikania: chemical composition and phytotherapeutical activity

The genus Mikania ranks high in the list of best-selling natural products in the world. Its main distribution is in South America, but some species are found in Asia, North America and Africa. It is used for treating fever, rheumatism, colds and respiratory diseases, as well as snake bites and scorpion stings, due to its broad spectrum of action. There are approximately 430 species of this genus and only 12% have been studied, highlighting their chemical and pharmacological diversity. The main chemical groups are: coumarins and derivatives, sesquiterpenes, sesquiterpenes lactones, diterpenes, phytosterols/terpenoids and flavonoids. This review aims to supply useful references for scientists interested in natural products and the search for new compounds, from over the 300 already described for the genus.

Environmental control of adventitious rooting in Eucalyptus and Populus cuttings

Key messageConcerted control of irradiance, temperature, water availability, mineral nutrition and beneficial root-associated microorganisms significantly improves adventitious rooting in eucalypts and poplars, essentially by modulating auxin and carbohydrate metabolism.AbstractEucalyptus and Populus are among the most economically relevant tree genera. Clonal propagation allows fast genetic gain obtained using elite genotypes. Adventitious rooting (AR), a complex and multifactorial process, is often the main limiting factor for tree cloning. Herein, practical and basic approaches to optimize clonal propagation of eucalypts and poplars, focusing on the main environmental control factors affecting it, are explored. Auxin homeostasis and function are central to AR. Irradiance quality and quantity, as well as temperature, can effectively modulate auxin availability, transport and activity. The interaction of carbohydrates, irradiance and temperature is also at the core of AR. Root architecture may be effectively modified by different N sources. Several macro and micronutrients impact on central factors of rhizogenesis, including energy metabolism, gene expression and enzymatic activities regulating auxin and other phytohormonal steady-states driving AR. Appropriate mineral nutrition is often determinant for successful AR and survival. Microbial associations with the root system and the rhizosphere, both bacterial and fungal, can have a role in auxin availability to cuttings, as well as improve disease resistance, nutrition and water relations. Significant cost reduction in clonal propagation systems of eucalypt and poplar are attainable with an adequate control of environmental factors, particularly for donor plants. Future studies should extend the molecular and physiological findings of basic research to the commercial propagation systems, and these, by their turn, should be explored to provide further advances in the basic understanding of this crucial developmental process for human economy.

In vitro antifungal activity of four chemotypes of Lippia alba (Verbenaceae) essential oils against Alternaria solani (Pleosporeaceae) isolates

Several volatile natural compounds produced by plant secondary metabolism have been proven to present antimicrobial action, enabling their use in phytopathogen control. They also present low environmental impact when compared to conventional pesticides. Essential oils contain these compounds and can be found in several plant species, such as Lippia alba (Mill.) N.E. Brown (Verbenaceae). Essential oils of four chemotypes of L. alba, characterized by their major compounds, namely camphor, citral, linalool and camphor/1,8-cineole, were tested against the phytopathogen Alternaria solani Sorauer (Pleosporaceae), which causes early blight on tomatoes and is responsible for great economic losses regarding production. Essential oils antifungal action was tested in vitro using potato dextrose agar medium with essential oil concentrations at 0.1, 0.5, 1.0, 1.5 and 2.0 µL mL-1. The chemotype that had the best performance was citral, showing significant inhibition compared to the others, starting at the 0.5 µL mL-1 concentration. The essential oil belonging to the linalool chemotype was efficient starting at the 1.5 µL mL-1 concentration. Conversely, the camphor chemotype did not show any action against the phytopathogen. Moreover, the essential oils had no remarkable effect on tomato germination and growth. In conclusion, these essential oils presented fungicidal action against A. solani.

Checkmite!? Is the Resistance to Phytophagous Mites on Short and Stocky Wild Oryza Species?

Graduate Program in Biotechnology, University of Taquari Valley, Univates, Lajeado, Brazil, 2 Biological Sciences and Health Center, University of Taquari Valley, Univates, Lajeado, Brazil, Graduate Program in Biotechnology, University of Caxias do Sul, Caxias do Sul, Brazil, Graduate Program in Agrobiology, Federal University of Santa Maria, Santa Maria, Brazil, Graduate Program in Cell and Molecular Biology, Federal University of Rio Grande do Sul, Porto Alegre, Brazil

High infestation levels of Schizotetranychus oryzae severely affects rice metabolism

High levels of Schizotetranychus oryzae phytophagous mite infestation on rice leaves can severely affect productivity. Physiological characterization showed that S. oryzae promotes a decrease in chlorophyll concentration and the establishment of a senescence process in rice leaves. Late-infested leaves also present high levels of superoxide radical and hydrogen peroxide accumulation, along with high levels of membrane integrity loss, which is indicative of cell death. To better understand the rice molecular responses to high levels of mite infestation, we employed the Multidimensional Protein Identification Technology (MudPIT) approach to identify differentially expressed proteins. We identified 83 and 88 proteins uniquely present in control and late-infested leaves, respectively, along with 11 and one proteins more abundant in control and late-infested leaves, respectively. S. oryzae infestation induces a decreased abundance of proteins related to translation, protease inhibition, and photosynthesis. On the other hand, infestation caused increased abundance of proteins involved in protein modification and degradation. Our results also suggest that S. oryzae infestation interferes with intracellular transport, DNA structure maintenance, and amino acid and lipid metabolism in rice leaves. Proteomic data were positively correlated with enzymatic assays and RT-qPCR analysis. Our findings describe the protein expression patterns of late-infested rice leaves and suggest several targets which could be tested in future biotechnological approaches aiming to avoid the population increase of phytophagous mite in rice plants.

Phytotoxic effects of extract and essential oil of Eucalyptus saligna (Myrtaceae) leaf litter on grassland species

Under Eucalyptus plantations in the South Brazilian grassland region, few plants establish, and allelopathy may be involved in shaping this pattern. We aimed to assess the phytotoxicity of essential oil and aqueous extract of Eucalyptus saligna Sm. leaf litter on grassland species. We tested the effects of E. saligna pure oil and extract on germination, seedling growth, H2O2 levels and electrolyte leakage of seedling membranes of Paspalum notatum Flugge, Eragrostis plana Ness (Poaceae), Trifolium repens L. and Lotus corniculatus L. (Fabaceae). Essential oil and aqueous extract of E. saligna affected all recipient species, even at the lowest amounts/concentrations, inhibiting germination and initial growth, and also increasing H2O2 levels and electrolyte leakage of seedling membranes. Essential oil consisted mainly of monoterpenes and presented α-pinene and 1,8-cineole as the major compounds. The extract contained phenolics, and lower levels of these compounds in the extract were associated with decreased phytotoxicity. We conclude that E. saligna contains phytotoxic compounds in leaf litter that generate oxidative stress and lead to membrane damage, affecting seeds and seedling growth. In addition, we relate E. saligna phytotoxicity to monoterpenes that may be released from leaf litter by volatilisation, and phenolics that may be leached by rainfall. Our study indicates that E. saligna has allelopathic potential on the tested grassland species.

Nitrogen Sources and Adventitious Root Development in Eucalyptus globulus Microcuttings

In previous studies, it has been shown that nitrate supply may favor adventitious rooting in the rooting recalcitrant Eucalyptus globulus. Herein, the impact of various N sources on adventitious rooting and root branching in microcuttings of E. globulus was investigated. The positive effect of nitrate on adventitious root development was confirmed and extended to root branching. Urea yielded a rooting response comparable to that observed in presence of nitrate. Urease activity was observed, displaying two peaks: one at the root induction and another at the root formation step. The use of glutamic acid, glutamine or asparagine promoted higher root number, but yielded shorter roots. Rooted microcuttings derived from all nitrogen (N) sources were successfully acclimated to ex vitro conditions. The manipulation of N sources in adventitious rooting media can be a tool for improving new root density, length and branching in this species.

Oryza brachyantha A. Chev. et Roehr

The growing interest in the Oryza genus comes from the feasibility of studying genome evolution of these closely related species, as well as the direct impact of identifying desirable phenotypes that could be transferred to Oryza sativa, one of the world’s most important cereals. Among the Oryza species, Oryza brachyantha is unique: it is highly divergent, has the smallest genome in the genus and is the only FF species, and has several traits that could be useful to improve Oryza sativa. However, our understanding of the basic biology of O. brachyantha and conservation of its diversity in germplasm are still preliminary. In this chapter, we summarize the current knowledge on O. brachyantha, especially on its recently published genomes (nuclear and chloroplastidic), basic genetics, and sequence comparisons with other Oryza species. The information gathered here should be useful to guide efforts to conserve and explore O. brachyantha diversity, a necessary step in order to achieve both basic and applied science goals in the future.