Resumo

ALMANZA M., Pedro José et al. Foliar nickel application to Cucurbita ficifolia Bouché for crystalline urease (EC 3.5.1.5) production  . Agron. colomb. [online]. 2009, vol.27, n.1, pp.33-40. ISSN 0120-9965.

The effect of nickel foliar application to plants of Cucurbita ficifolia (tropical squash) was evaluated at 1.0, 2.5 and 5.0 mg L^-1 concentrations, and on a control experiment, in terms of later extraction of crystalline urease from the seeds. This work is intended to contribute to studies that aim at increasing the production of this enzyme, which is closely related to nickel. Thus, after determining seed nickel and urease contents, the extracted enzyme was lyophilized. The effects of enzyme and substrate concentrations, temperature and pH on extracted urease catalytic activity were analyzed and compared to conventional clinical urease, by testing their performance on urine samples. Nickel applications were found to cause phytotoxicity on all plants. Plant growth and vegetative development were registered from the initial application through fructification. Fruit and seed growth were indirectly proportional to the concentrations used. The 5.0 mg L^-1 Ni concentration caused flower senescence in 100% of the plants, therefore preventing fructification. The 1.0 and 2.5 mg L^-1 concentrations were tolerated by the plants, but intervein chlorosis was observed. Contrarily, extracted urease amounts were directly proportional to applied Ni concentrations. In all cases, urease catalytic response to Ni concentration was maximum at 1.0 mg L^-1, medium for the control treatment, and minimum at 2.5 mg L^-1. The extracted urease had a weaker performance when compared to the commercial one.

Palavras-chave : catalytic activity; enzymes; seeds; phytotoxicity; lyophilization.

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