Termos para indexação: nutrientes, Zea mays, mucuna anã, guandu anão, Crotalaria spectabilis, feijão-de-porco.(1) Suporte financeiro FAPESP. Recebido para publicação em agosto de 2002 e aprovado em dezembro de 2004.
Nickel (Ni) toxicity has been reported to decrease productivity in soybean (Glycine max L.). However, soybean responses to Ni toxicity are not well understood. The aim of the present study was to describe Ni toxicity in soybean plants through physiological, nutritional, and ultrastructural analyses. Plants were grown in nutrient solution containing increasing Ni concentrations (0, 0.05, 0.1, 0.5, 10, and 20 μmol L −1), and nutritional, anatomical, physiological and biochemical features were determined. The results revealed previously unreported detrimental effects of Ni toxicity on soybean plants. CO 2 assimilation rates, stomatal conductance and transpiration decreased, resulting in lower biomass in soybean plants exposed to the highest Ni levels. Nitrate reductase activity increased with up to 0.05 μmol L −1 Ni and then decreased, indicating halted N-metabolism. Urease activity increased with increasing Ni availability in the nutrient solution, and peroxidase and superoxide dismutase activities were higher in plants grown at higher Ni levels. Leaf epidermal thickness (abaxial and adaxial), as well as root xylem and phloem diameter, decreased starting at 0.1 μmol L −1 Ni. Mean Ni concentrations varied from 77.5 to 17,797.4 mg kg −1 in roots and 2.3 to 16,774.5 mg kg −1 in shoots. Soybean plants exhibited symptoms of Ni toxicity starting at 0.1 μmol L −1 Ni, presenting mean shoot Ni concentration of 28.9 mg kg −1 , along with leaf water loss until complete drying. The results contribute to our understanding of several physiological, biochemical and histological mechanisms of Ni toxicity in soybean, which is still poorly understood.
Aluminium (Al) is a toxic element for plants living in soils with acidic pH values, and it causes reductions in the roots and shoots development. High Al concentrations can cause physiological and structural changes, leading to symptoms of toxicity in plant tissue. The aim of this study was to describe the Al toxicity in soybean plants through physiological, nutritional, and ultrastructure analyses. Plants were grown in nutrient solution containing increasing Al concentrations (0; 0.05; 0.1; 1.0, 2.0 and 4.0 mmol L). The Al toxicity in the soybean plants was characterized by nutritional, anatomical, physiological, and biochemical analyses. The carbon dioxide assimilation rates and stomatal conductance were not affected by the Al. However, the capacity for internal carbon use decreased, and the transpiration rate increased, resulting in increased root biomass at the lowest Al concentration in the nutrient solution. The soybean plants exposed to the highest Al concentration exhibited lower root and shoot biomass. The nitrate reductase and urease activities decreased with the increasing Al concentration, indicating that nitrogen metabolism was halted. The superoxide dismutase and peroxidase activities increased with the increasing Al availability in the nutrient solution, and they were higher in the roots, showing their role in Al detoxification. Despite presenting external lesions characterized by a damaged root cap, the root xylem and phloem diameters were not affected by the Al. However, the leaf xylem diameter showed ultrastructural alterations under higher Al concentrations in nutrient solution. These results have contributed to our understanding of several physiological, biochemical and histological mechanisms of Al toxicity in soybean plants.
RESUMO-Este trabalho buscou avaliar a aplicação dos fitorreguladores químicos na qualidade tecnológica do sorgo sacarino. O ensaio foi realizado na Usina Cerradinho, localizada em Catanduva-SP. O delineamento experimental utilizado foi em blocos casualizados, no esquema de parcelas subdivididas, em que os tratamentos foram constituídos pela combinação de dez tratamentos envolvendo as aplicações dos fitorreguladores químicos: 5; 10; 20 g ha-1 sulfometuron-methyl; 0,10; 0,20; 0,40 L ha-1 glifosate; 0,2; 0,4; 0,8 L ha-1 ethyl-trinexapac e testemunha. Nos subtratamentos, foram realizadas as amostragens para as avaliações da qualidade tecnológica em épocas distintas após aplicação dos maturadores químicos. A área foi dividida em quatro repetições, cada parcela foi formada de cinco linhas espaçadas de 0,75 m entre si, por 10 m de comprimento, constituída pela cultivar de sorgo sacarino Biomatrix 535. Foram avaliadas qualidades tecnológicas como: pureza (% caldo); açúcares redutores; açúcares redutores totais; brix (% caldo); pol (% caldo); açúcares teóricos recuperáveis; e fibra (%). Os fitorreguladores químicos glifosate na dose de 0,40 L ha-1 e ethyltrinexapac nas dosagens de 0,20; 0,40 e 0,80 L ha-1 promoveram maior incremento na qualidade tecnológica do sorgo sacarino. As épocas de colheita não influenciaram nas características tecnológicas do sorgo sacarino.
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