ABSTRACT: In this work, we compared nitrate-supplied plants (non-nodulated) with non-nitrate-supplied plants (nodulated) under oxygen privation of root system (hypoxia) and re-oxygenation (post-hypoxia; recovery) in order to verify whether N sources affect the antioxidant system during oxidative stress caused by hypoxia and post-hypoxia conditions. Antioxidant enzymatic activities, ascorbate redox state, and reactive oxygen species (ROS) levels were analyzed in roots and leaves of two soybean genotypes, Fundacep 53 RR and BRS Macota at reproductive stage R2, during hypoxia and post-hypoxia in an experiment carried out in a hydroponic system. The antioxidant system was strongly induced in roots of nitrate-supplied plants of both genotypes, with high activity of superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase and guayacol peroxidase. It also increased reduced ascorbate and ascorbate redox state and decreased ROS production under hypoxia and recovery, while in leaves of nodulated and non-nodulated plants, a slight increase on antioxidant system was observed. Nitrate may benefit soybean plants under hypoxic conditions and subsequent re-oxygenation by inducing the antioxidant system mainly in roots to cope with ROS production and reduce oxidative damage.

Este trabalho investiga o efeito do ácido salicílico (um elicitor abiótico) sobre a atividade antioxidante e produção de betacianinas em folhas de Alternanthera tenella cultivada in vitro. As plantas foram cultivadas em meio MS líquido e vermiculita como substrato. Após 35 dias, o ácido salicílico foi adicionado ao meio. Conteúdo de betacianinas, fenóis totais e flavonoides e a capacidade antioxidante não-enzimática foi determinada em folhas de A. tenella após 0, 12, 36 e 48h de tratamento. Após 36h, a concentração de betacianinas e fenóis totais aumentaram. Em contrapartida, o aumento no tempo de exposição causou uma ligeira diminuição nos teores de flavonoides totais e inibição da atividade do radical livre DPPH. Como resultado, a atividade antioxidante de folhas de A. tenella é promovida pelo ácido salicílico e pode ser atribuída ao aumento do conteúdo de betacianina, os quais são compostos com ação antioxidante reconhecida.

This research investigates effects of salicylic acid (an abiotic elicitor) on the antioxidant activity and betacyan production from leaves of Alternanthera tenella cultured in vitro was evaluated. Plants were grown in a liquid MS medium and vermiculite substrate. After 35 days salicylic acid was added to the medium. Content of betacyanins, total phenols and flavonoids and non-enzymatic antioxidant capacity were determined in leaves of A. tenella after 0, 12, 36 and 48h of treatment. After 36h, concentration of betacyanins and total phenols increased. On the other hand, the increase of the treatment time caused a slight decrease in total flavonoids and reduced the DPPH free radical activity. As result the antioxidant activity of the leaves of A. tenella is promoted by salicylic acid and can be attributed to the increase in betacyanin content, which are compounds with recognized antioxidant action.

A espécie Achillea millefolium L., conhecida como mil-folhas, é uma planta herbácea, rizomatosa e perene. Sua importância medicinal deve-se às suas atividades antibacterianas, antiinflamatórias, antitumorais, analgésicas e antioxidantes. O efeito da disponibilidade de luz e do nitrogênio sobre o crescimento e produção dessa espécie é pouco conhecido. O objetivo deste trabalho foi avaliar a resposta de A. millefolium L., cultivada sob diferentes níveis de sombreamento e doses de nitrogênio, quanto ao crescimento e à produção de pigmentos fotossintéticos. As plantas foram cultivadas sob três doses de nitrogênio (0, 75 e 150kg uréia ha-1) e submetidas a dois níveis de sombreamento 0% (luz plena) e 75% (sombrite 75%). Adotou-se o delineamento experimental de blocos casualizados com quatro repetições em um fatorial 3x2 (doses de nitrogênio x níveis de sombreamento). O sombreamento influenciou a maioria dos caracteres avaliados, causando uma redução significativa no acúmulo de massa seca da parte aérea (caule + folha + flor), caule, folhas e flores e aumento nos teores de clorofila a, b, total e carotenóides. Os resultados sugerem que a espécie A. millefolium L. possui adaptação à baixa intensidade luminosa, devido às alterações nas características foliares, relacionadas aos teores de pigmentos fotossintéticos.

Achillea millefolium L., known as yarrow, is an herbaceous, rhizomatous and perennial plant. Its medicinal importance is attributed to antibacterial, anti-inflammatory, antitumoral, analgesical and antioxidant activities. The effect of light availability and nitrogen on growth and production of this species is little known. The objective of this study was to evaluate the growth and production of photosynthetic pigments in A. millefolium L. grown under different levels of shading and nitrogen levels. Plants were cultivated under three nitrogen levels (0, 75 and 150kg urea ha-1) and subjected to two levels of shading 0% (full light) and 75% (75% black). The experimental design was delineated in randomized blocks with four replicates in a factorial 3 x 2 (nitrogen levels x levels of shading). The shading influenced most parameters evaluated, causing a significant reduction in dry mass accumulation of shoot (stem + leave + flower), stem, leaves and flowers and increase in levels of chlorophyll a, b, total and carotenoids. Results suggest that Achillea millefolium L. has adaptated to low light intensity, due to changes in leaf traits related to photosynthetic pigments content.