Alterações fisiológicas em sementes e plantas de feijão carioca resultantes da contaminação por rejeitos de mineração

Abstract

Environmental disasters, like the one that happened at Mariana (state of Minas Gerais), are among the main reason for soil residue accumulation, caused by many types of heavy metals, such as iron oxide (Fe2O3) and zinc oxide (ZnO). The objective of this research was to evaluate changes, induced by different concentrations of Fe2O3 and ZnO, in the physiological quality of seeds and in the metabolism of Phaseolus vulgaris L. plants. The study was divided into two experiments; in the first one, the effect of the compounds on the physiological potential of seeds and initial growth of the seedlings was estimated. Pinto bean seeds were submitted to different Fe2O3 (0.0; 5.0 10.0 and 20.0mg L-1) and ZnO (0.0; 5.0; 7.5 and 10.0mg L-1) concentrations. Subsequently, in the second experiment, the plants were cultivated in substrate and upon reaching growth stage V2, were moved to a hydroponic system and subjected to the same Fe2O3 e ZnO concentrations. After a fourteen-day period, analysis were performed, in order to evaluate growth parameter, chloropyll indicators, flavonoids, anthocyanins, nitrogen balance, gas exchange, chlorophyll a transient fluorescence, activity of antioxidant enzymes and the mineral profile of the plants during the work. Results attested that the two oxides caused reduction in the growth parameters, but did not interfere in the germination potential of the seeds. Chloropyll and flavonoid indicators experienced an increase, whereas the nitrogen balance and anthocyanin levels showed no changes. There was a significant decline on the photosynthetic rate, CO2 assimilation, stomatal conductance and transpiration measurements, even though the water usage efficiency and water intrinsic efficiency levels went up. Chlorophyll a transient fluorescence rates showed damage to photosystem I. It was also observed a growth reduction of the aerial part of the plants and their root system. Regarding the antioxidant enzymes, values remained close to the control. The mineral profile displayed that heavy metals generate a dramatic nutritional imbalance. Therefore, it can be concluded that iron and zinc oxide metals at high levels cause damage to growth and physiological metabolism in pinto bean plants.