Abstract Heavy metals are natural non-biodegradable constituents of the Earth's crust that accumulate and persist indefinitely in the ecosystem as a result of human activities. Since the industrial revolution, the concentration of cadmium, arsenic, lead, mercury and zinc, amongst others, have increasingly contaminated soil and water resources, leading to significant yield losses in plants. These issues have become an important concern of scientific interest. Understanding the molecular and physiological responses of plants to heavy metal stress is critical in order to maximize their productivity. Recent research has extended our view of how plant hormones can regulate and integrate growth responses to various environmental cues in order to sustain life. In the present review we discuss current knowledge about the role of the plant growth hormones abscisic acid, auxin, brassinosteroid and ethylene in signaling pathways, defense mechanisms and alleviation of heavy metal toxicity.

O estudo dos efeitos do vigor das sementes sobre os estádios iniciais do desenvolvimento das plântulas de soja é importante, já que compreendem o período de estabelecimento da cultura. Sementes de baixo vigor podem provocar reduções na velocidade de emergência e na produção de biomassa seca de plântulas, podendo afetar o estabelecimento da cultura. Este estudo teve por objetivo quantificar os componentes químicos e avaliar a capacidade de mobilização de reservas, na germinação de sementes de soja de alto e baixo vigor. Foram utilizadas três cultivares: BRS 243RR, BRS 246RR e CD 219RR. A caracterização do vigor foi por meio do teste de envelhecimento acelerado. Para determinação da composição química das sementes, foram quantificados os teores de proteínas, amido e açúcar solúvel, além da atividade da isoenzima alfa amilase. A capacidade de mobilização das reservas na germinação foi avaliada por meio da massa seca e do comprimento das plântulas. De acordo com os resultados desse trabalho, em sementes mais vigorosas há maiores conteúdos de proteínas solúveis, amido e açúcares solúveis, bem como maior capacidade de mobilização de reservas na germinação, resultando em plântulas de soja com melhor desempenho inicial.

The study of vigour effect on the initial stages of soybean seeds development is important, once it includes the period of crop establishment. Seeds with low vigour may result in reduction of emergence rate and dry matter production, which may affect the crop establishment. The aims of this study were to quantify chemical components and to evaluate the capacity of seed reserve mobilization in germination of soybean seeds with high and low vigour. Three cultivars, BRS 243RR, BRS 246RR and CD 219RR were studied. The characterization of seed vigour was performed by the accelerated aging test. To determine seed chemical composition, soluble sugar, starch and soluble protein were quantified; in addition alpha amylase isoenzyme activity was also evaluated. The capacity of seed reserve mobilization during germination was evaluated by seedling dry matter and length. According to the results of this study, high vigour soybean seeds exhibit higher content of soluble proteins, starch and soluble sugars. Besides, they showed higher capacity of seed reserve mobilization during germination, resulting in a better performance for seedlings development.