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Tithonia diversifolia, a ruderal weedy species utilized in agroforestry, is widely distributed in the tropics, often being found in wasteland, margins of polluted city rivers and roadsides. The objective of this study was to compare plants sampled at a light and heavy traffic roadside for metal concentration and foliar compounds which may be related to senescence and/or detoxification of metals. The field survey was followed by an experiment in pots of Pb-acetate-supplemented soil to verify if the same response is obtained under controlled conditions with regard to Pb. The concentration of Pb in leaves and roots of plants sampled at a heavy traffic roadside was higher than in samples from a light traffic site. The content of Cr, Al, Fe, Cu and Ni was also higher in leaves but not of roots in plants from the pollutedsite. No significant differences were found in the concentrations of chlorophyll, carotenoids, UV-absorbing compounds and proteins, nor in the chlorophyll a/b ratio and lipid peroxidation of leaves collected at both sites. On the other hand, Pb-contaminated leaves and roots showed higher acid phosphatase activity while the foliar nitrate reductase activity and specific leaf mass were lower. An increase of leaf phenol concentration, thought to be involved in the detoxification of metals, was observed in the polluted field plants and in roots in the pot experiment, where Pb-acetatewas supplied to the soil, but the changes observed in acid phosphatase and specific leaf mass in the field were not found in the pot experiment. Tithonia diversifolia, uma espécie ruderal utilizada em sistemas agroflorestais, amplamente distribuída nos trópicos, é freqüentemente encontrada em locais de descarte, margens de rios poluídos próximos a cidades e ao longo de rodovias. O objetivo deste estudo foi comparar plantas coletadas de rodovias com pouco e com intenso tráfego em relação à concentração de metais e compostos foliares que podem estar relacionados à senescência e/ou à destoxificação de metais. Também fez-se um experimento com vasos contendo solo suplementado com chumbo para verificar se a mesma resposta é obtida sob condições controladas usando esse metal. A concentração de Pb nas folhas e raízes de plantas amostradas em rodovia de tráfego intenso foi maior que nas amostras de rodovia de pouco tráfego. As concentrações de Cr, Al, Fe, Cu e Ni foram maiores nas folhas, mas não nas raízes de plantas da rodovia de tráfego intenso. Não houve diferença significativa nos conteúdos de clorofila, carotenóides, compostos absorvendo no UV e proteínas, como também na razão clorofilas a/b e peroxidação de lipídeos das folhas coletadas em ambas as rodovias. Por outro lado, folhas de plantas contaminadas com Pb mostraram maior atividade de fosfatase ácida, enquanto a atividade foliar da redutase do nitrato e a massa foliar específica foram menores. Aumento na concentração de fenóis, o que se pensa estar envolvido na destoxificação de metais, foi observado nas plantas coletadas na rodovia de tráfego pesado e nas raízes do experimento com vasos, no qual Pb foi adicionado ao solo. Todavia, as alterações de fosfatase ácida e massa foliar específica não foram observadas nesse experimento

The effect of lead on the phytochemistry of Tithonia diversifolia exposed to roadside automotive pollution or grown in pots of Pb-supplemented soil