Photosynthesis, gas exchange and antioxidative response in Canavalia ensiformis and Stizolobium aterrimum exposed to toxic levels of arsenic / Fotossíntese, trocas gasosas e respostas antioxidativas em Canavalia ensiformis e Stizolobium aterrimum submetidas a níveis tóxicos de arsênio

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Canavalia ensiformis and Stizolobium aterrimum species grown in nutrient solution, pH 5.5, were treated with arsenic (As) at 0.0; 1.5; 2.5 and 3.5 mg L-1 concentrations during five days. After plant treatment As content and dry mass yield were determined. Arsenic effect on physiological and antioxidative parameters were also studied in the two species exposed to 0 and 1.5 mg L-1 As concentrations. Arsenic contents in plant roots and shoots increased with the increase in As in the nutrient solution, always at higher rates in C. ensiformis. Wilting of leaves was observed in C. ensiformis at 2.5 and 3.5 mg L-1 As concentrations, but not in S. aterrimum. Both species showed As toxicity symptoms in the roots. S. aterrimum showed darkening and diameter increase of lateral roots. C. ensiformis showed root yellowing only when exposed to 1.5 mg L-1 As concentration, followed by an increase in toxicity symptoms intensity and root system disintegration as As concentration was increased. Reduction of root hair number occurred in both species, with higher intensity in C. ensiformis. The species showed dry mass reduction in both plant parts, especially in the shoots. Chlorophyll a, b and total and carotenoids contents increased in C. ensiformis, but did not change in S. aterrimum with As treatment. Arsenic reduced CO2 assimilation rate, transpiration rate (E), stomatal conductance (gs), internal to external CO2 concentration ratio (Ci/Ca) and internal CO2 concentration (Ci) in both species, especially in C. ensiformis. Initial fluorescence (F0) and variable fluorescence to maximum fluorescence ratio (Fv/Fm) did not change in both species exposed to As. Plants exposure to As resulted in superoxide dismutases (SODs) activity increase in roots and leaves in both species. Peroxidases (POXs) activity decreased in both plant parts of S. aterrimum, but increased in C. ensiformis with As treatment. Glutathione reductases (GRs) activity increased in the roots of both species, especially in S. aterrimum. In the leaves, however, GRs activity increased only in C. ensiformis, while in S. aterrimum enzyme activity reduced. Lipid peroxidation in roots and leaves increased in both species after As treatment, especially in S. aterrimum. Under the experimental condition used in this research S. aterrimum was considered more tolerant to the toxic effects of As than C. ensiformis.

ASSUNTO(S)

stress estresse arsênio fisiologia vegetal fitorremediação arsenic toxicity toxidez phytoremediation

ACESSO AO ARTIGO

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