Hélio Nitta Matsuura

Oxidative stress and production of bioactive monoterpene indole alkaloids: biotechnological implications

Monoterpene indole alkaloids (MIAs) encompass plant natural products with important pharmacological relevance. They include the anti-tumoral MIAs found in Catharanthus roseus and Camptotheca acuminata. The often low yields of bioactive alkaloids in plants has prompted research to identify the factors regulating MIA production. Oxidative stress is a general response associated with biotic and abiotic stresses leading to several secondary responses, including elicitation of MIA production. These changes in secondary metabolism may take place directly or via second messengers, such as Ca2+ and reactive oxygen species (ROS). H2O2 is the main ROS that participates in MIA biosynthesis. This review analyzes the links between oxidative stress, elicitation of bioactive MIA production and their potential roles in antioxidant defense, as well as exploring the implications to developing biotechnological strategies relevant for alkaloid supply.

The major indole alkaloid N,β-D-glucopyranosyl vincosamide from leaves of Psychotria leiocarpa Cham. & Schltdl. is not an antifeedant but shows broad antioxidant activity

N,β-D-glucopyranosyl vincosamide (GPV), a major alkaloid of Psychotria leiocarpa, constitutes up to 2.5% of the dry weight in leaves. Alkaloid content was not elicited by mechanical wounding or jasmonate. At concentrations found in natural conditions or 2.5 fold higher, GPV did not inhibit herbivory in two unrelated generalist models (Helix aspersa and Spodoptera frugiperda) or in a specific interaction model (Heliconius erato fed with Passiflora suberosa). In situ staining assay showed quenching activity of hydrogen peroxide by GPV. Exposure of P. leiocarpa to acute UV-B stress did not change GPV or chlorophyll content, indicating high tolerance to this stress by the species. In vitro antioxidant tests against singlet oxygen, superoxide anions and hydroxyl radicals showed efficient quenching activity of the alkaloid. GPV was not effective as antifeedant, but it may act indirectly in P. leiocarpa protection against oxidative stress generated upon wounding, UV exposure and perhaps other environmental stresses.

Photoelicitation of Bioactive Secondary Metabolites by Ultraviolet Radiation: Mechanisms, Strategies, and Applications

As sessile organisms, plants are exposed to various environmental factors that lead to changes in physiology and morphology. One of these factors is ultraviolet radiation. Plants have protective mechanisms, both constitutive and induced, or can activate repair responses to cope with UV-B stress. One of the most common protective responses is the accumulation of secondary metabolites capable of absorbing radiation in the ultraviolet wavelength range, such as anthocyanins, flavonols, and flavones. These compounds can also scavenge free radicals, mainly reactive oxygen species (ROS). Examples of UV-induced accumulation of compounds belonging to virtually all classes of secondary metabolites are available. Exposure to UV-B radiation stimulates expression of an array of genes involved in defense responses. Increased input of UV light has been shown to increase ROS production, activity of antioxidative enzymes, and secondary metabolite pathways in different plant species. UV is a powerful tool to modulate secondary metabolism pathways in plants. Besides field level manipulation of UV-B incidence, the use of acute treatments and UV-C pulses may be useful strategies for changing profiles and yields of plant secondary compounds of medicinal interest at commercial scale.

Events Associated with Early Age-Related Decline in Adventitious Rooting Competence of Eucalyptus globulus Labill

The development of adventitious roots is affected by several factors, including the age of the cutting donor plant, which negatively affects rooting capacity. Eucalyptus globulus quickly loses rooting capacity of cuttings as the donor plant ages, although the molecular and biochemical mechanisms behind this process are still unclear. To better understand the bases of rooting competence loss in E. globulus, the time required for a significant decline in rhizogenic ability without exogenous auxin was determined in microcuttings derived from donor plants of different ages after sowing. Tip cuttings of donor plants were severed before and after loss of rooting competence of microcuttings to test the hypothesis that auxin and carbohydrate homeostasis regulate rooting competence decline. There were no significant changes in concentration of carbohydrates, flavonoids, or proteins before and after the loss of rooting capacity. Peroxidase (EC 1.11.1.7) total activity increased with loss of rooting competence. Auxin concentration showed the opposite pattern. In good agreement, TAA1, a key gene in auxin biosynthesis, had lower expression after loss of rooting capacity. The same applied to the auxin receptor gene TIR1, suggesting reduced auxin sensitivity. On the other hand, genes associated with auxin response repression (TPL, IAA12) or with the action of cytokinins, the rhizogenesis inhibitor-related ARR1, showed higher expression in plants with lower rooting competence. Taken together, data suggest that age negatively affects E. globulus rooting by a combination of factors. Decreased endogenous auxin concentration, possibly caused by less biosynthesis, lower auxin sensitivity, higher expression of genes inhibiting auxin action, as well as of genes related to the action of cytokinins, appear to play roles in this process.

Specialized Plant Metabolism Characteristics and Impact on Target Molecule Biotechnological Production.

Plant secondary metabolism evolved in the context of highly organized and differentiated cells and tissues, featuring massive chemical complexity operating under tight environmental, developmental and genetic control. Biotechnological demand for natural products has been continuously increasing because of their significant value and new applications, mainly as pharmaceuticals. Aseptic production systems of plant secondary metabolites have improved considerably, constituting an attractive tool for increased, stable and large-scale supply of valuable molecules. Surprisingly, to date, only a few examples including taxol, shikonin, berberine and artemisinin have emerged as success cases of commercial production using this strategy. The present review focuses on the main characteristics of plant specialized metabolism and their implications for current strategies used to produce secondary compounds in axenic cultivation systems. The search for consonance between plant secondary metabolism unique features and various in vitro culture systems, including cell, tissue, organ, and engineered cultures, as well as heterologous expression in microbial platforms, is discussed. Data to date strongly suggest that attaining full potential of these biotechnology production strategies requires being able to take advantage of plant specialized metabolism singularities for improved target molecule yields and for bypassing inherent difficulties in its rational manipulation.

In vitro antioxidant activity of alkaloids from southern Brazilian Psychotria: a comparative analysis.

Background Monoterpene indole alkaloids (MIAs) comprise a class of secondary metabolites of dual biosynthetic origin, characterized by the presence of an indole and a terpene portion. MIAs are widely studied because of their bioactive properties and pharmacological potential. In this study, major MIAs from native species of Psychotria of southern Brazil were used: P. brachyceras, P. umbellata and P. leiocarpa share the same habitat and accumulate the alkaloids brachycerine, psychollatine and N,b-D-glucopyranosyl vincosamide, respectively. The three MIAs are related and have structural similarities. Previous work identified antioxidant properties of these alkaloids and induction of their accumulation by oxidative stress, suggesting that they play roles as antioxidant compounds, something regarded as unusual for this metabolite class [1]. MIAs may have a role on control of oxidative burst generated by stress, aiming at reducing the reactive oxygen species’ harmful effects and promoting the maintenance of plant fitness. Herein, the antioxidant potential of the three alkaloids against superoxide anions and singlet oxygen is comparatively evaluated, and putative structure-activity relations are considered.