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Six S5 lines of maize, with differences for lysine and oil contents in grains, were used to carry out a complete series of diallelic crosses. The resulting 15 hybrids were grown in a field at two nitrogen levels (10 and 130 kg N ha-1). The general combining ability (GCA) and specific combining ability (SCA) were obtained by using the method 4, model I of Griffing for grain yield, and grain lysine and oil contents. Significant (p < 0.001) interaction was observed between GCA and N levels for grain yield, indicating the selection of different lines for each N level. This interaction was not significant for lysine content, but there were significant effects of GCA for this trait at both N levels (p < 0.1). Significant effects were not observed for GCA or SCA for oil content, however a positive correlation was observed between lysine and oil contents in the hybrids, in the lines and even in the control cultivars. The results indicate the effectiveness of selection for lysine content, irrespective of N level, in the studied non-opaque maize lines, and the possibility of achieving both high lysine and oil content in grains.Seis linhagens S5 de milho, com diferenças para conteúdos de óleo e de lisina nos grãos, foram usadas para realizar uma série completa de cruzamentos dialélicos. Os 15 híbridos resultantes foram cultivados em campo com dois níveis de nitrogênio (10 e 130 kg N ha-1). A capacidade geral de combinação (CGC) e a capacidade específica de combinação (CEC) foram obtidas com o método 4, modelo I de Griffing para produtividade de grãos e concentração de lisina e óleo nos grãos. Interação significativa (p < 0.001) foi observada entre CGC e níveis de N para produtividade de grãos, indicando seleção de diferentes linhagens para cada nível de N. Esta interação não foi significativa para conteúdo de lisina, mas existiu efeito significativo (p < 0.1) da CGC nos dois níveis de N para esta variável. Os efeitos de CGC e CEC foram não significativos para conteúdo de óleo, contudo, foi observada correlação positiva entre conteúdos de lisina e óleo nos híbridos, nas linhagens e mesmo nas cultivares utilizadas como controle. Os resultados indicam a efetividade da seleção para conteúdo de lisina nas linhagens não opaco de milho estudadas, independente dos níveis de N, e a possibilidade de atingir concomitantemente maiores níveis de óleo e lisina nos grãos.

ABSTRACT: In general, the effects of Cadmium (Cd) on crop quality are evaluated solely by Cd accumulation in the edible plant parts; thus, the potential effects on several nutritional features are not often taken into account. This study evaluated Cd effects on the enzymatic activities of lysine (Lys) metabolism, storage protein and amino acid profile in maize. Stress parameters were also assessed. In vegetative organs, Cd was accumulated in the following decreasing order: roots > stems > leaves. Cadmium accumulation in grains decreased at grain maturity (from 0.25 to 0.07 µg g−1 DW). In leaves, neither hydrogen peroxide content nor superoxide dismutase, catalase, ascorbate peroxide and guaiacol peroxidase activities did not change in Cd-treated plants compared to control plants. Lipid peroxidation was not detected in immature grains and leaves of plants under Cd exposure, indicating that Cd accumulation mainly in the roots is a mechanism to avoid oxidative stress in aboveground parts of the plant. However, Lys metabolism in immature grains was modified, showing increases in the specific activities of aspartate kinase (AK) and dihydrodipicolinate synthase (DHDPS) after Cd exposure. AK sensitivity to Lys feedback inhibition increased, but decreased in DHDPS in Cd-treated plants, suggesting differential regulation for these enzymes. In mature grains, the Lys content did not change, while the proline content increased by 54 % in Cd-treated plants. This is the first report on Cd effects on amino acid profile, storage protein contents and enzymes from Lys metabolism in grains of a cereal plant species.