Respostas fisiológicas e bioquímicas de duas cultivares de batata (solanum tuberosum l.) expostas ao cádmio

Abstract

In much agricultural farmland, cadmium (Cd) concentrations are above the natural levels mainly due to anthropogenic actions such as metal liberation from industrial and agricultural sources. Therefore, it is necessary to study the toxicity and accumulation of this metal in plants used as food sources such as the potato (Solanum tuberosum L.). This study was carried out with the objective of identifying and characterizing physiologic and biochemical aspects of Cd toxicity such as growth analysis, mineral nutrient content and oxidative stress of two potato cultivars, Asterix and Macaca. The in vitro plantlets were exposed to five concentrations of Cd (0, 100, 200, 300, 400 and 500 μM) for 22 days to evaluate the effects on growth parameters and mineral nutrition. In the hydroponic system, the plantlets were exposed to four concentrations of Cd (0, 50, 100, 150 e 200 μM) for 7 days to evaluate the effects on growth parameters, mineral nutrition and oxidative stress. In both systems, in vitro and hydroponics, both potato cultivars, Asterix and Macaca, showed a reduction in shoot length, number of nodal segments, number of leaves, and number of roots with increasing Cd levels in substrate. The results mainly related to root length and to the production of fresh biomass of both potato cultivars grown in both systems allow us to infer that cv. Macaca is more sensitive to Cd than cv. Asterix when grown in vitro. However, in the hydroponic system, the opposite was verified. Cd concentrations in roots and shoot of potato plantlets grown either in vitro or hydroponically increased progressively with increasing Cd levels in substrate. Although Cd content in the potato tissues grown in hydroponics exhibited a linear behavior, in the plantlets grown in vitro the increase in Cd content showed an erratic behavior. This may be due to the fact that an increase in dry biomass was observed at the lowest Cd level, whereas a strong reduction of biomass was observed at the highest Cd level. In general, macro and micronutrient content was not altered by Cd in the plantlets grown hydroponically. However, in vitro, high Cd concentrations caused drastic reductions in the content of these mineral nutrients. In addition, the Macaca cultivar showed an increase in the content of some nutrients only when cultivated in vitro and exposed to low Cd levels, corroborating with the results observed for dry biomass production. The presence of Cd in the hydroponic system decreased the carotenoid content only in the Macaca cultivar, however it reduced the aminolevulinate dehydratase activity and chlorophyll content in both potato cultivars, indicating that Cd interferes negatively in processes related to photosynthesis. Cd increased malondialdehyde levels in the shoot and roots of both potato cultivars, and increased the carbonyl groups in the shoot of both potato cultivars at the highest Cd level. The increase in the hydrogen peroxide concentration indicates that Cd altered the production of reactive oxygen species leading to lipid peroxidation of the membranes and to protein oxidation in these plantlets. Cd caused alterations in the activity of antioxidant enzymes such as catalase and superoxide dismutase, besides altering the content of non-enzymatic antioxidants such as ascorbic acid and non-protein thiol groups. The alterations observed in the antioxidant defense system and mineral nutrient content of potato plantlets exposed to Cd indicate that this metal promoted oxidative stress and a nutritional imbalance in this species, which contributed to the negative effects observed in relation to its growth.