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Miguel Pedro de Freitas Barbosa Mourato (isa2559)
Site pessoal
Potentially toxic elements (PTE), like heavy metals, certain metalloids and some salts, can affect plant development and production yields of food crops. The stress induced by these PTE is a worldwide problem due to the increased soil and water pollution. Basil (Ocimum basilicum) is a culinary herb that has been increasingly used in modern cuisine. In this work, irrigation experiments were conducted in order to evaluate the basil’s phenotype response and cumulative capacity when exposed to stress induced by PTE through the determination of biomass, dry matter, chlorophyll content and mineral composition. Basil plants with 20 days growth were exposed to solutions containing 50 µM of Cd, 50 µM of As, 100 µM of Cu, and 25 mM of NaCl. This irrigation experiment lasted 100 days from sowing, with data collection and harvesting at the 52nd, 72nd, 86th and 100th day. The biomass of plants contaminated with As and NaCl was strongly affected, with less 40.7 % and 64.1 %, respectively, compared to control plants on the last day of the experiment,. However, only the leaves contaminated by Cd showed a considerable decrease in the dry matter content (7.2 %) when compared with the control (11.1 %). This implies a decrease in water intake and hence can also affect nutrient uptake. On the other hand, leaves contaminated with As showed a significantly higher dry matter content (12,8 %), indicating a stimulation of water uptake. Regarding the chlorophyll content, it was observed a significant decrease in the plants contaminated by Cd, evidenced by the manifestation of chlorosis in the leaf samples, mostly in young leaves. The same effect was also observed in Cu contaminated plants, although to a lesser extent. Thus, Cu and Cd seem to affect the plants photosynthetic system. This effect was not observed in samples contaminated with As and NaCl. Leaves contaminated with As and NaCl showed a darker but healthy colouring, probably because of a reduced leaf area. Regarding the mineral composition of Basil leaves, we concluded that As affected the uptake of essential elements to a greater extent. A lower absorption of Ca, Mg, Mn, K and Zn, compared to the control, was observed. The contamination with Cd, appears to stimulate the absorption of Ca, Mn and K only at the 86th and 100th days and to reduce the absorption of Cu, Fe and Zn. Copper contamination appears to reduce the absorption of Mg, Zn and Fe, while not significantly stimulating the absorption of any element. In the experiments with NaCl, the absorption of Fe was stimulated and the absorption of Ca, Mg, Zn and Mn was reduced. We thus confirmed that the contamination with Cd, As, Cu and NaCl has affected the composition of other important elements in basil plants. At the last day of the experiment, basil was able to uptake 6.29 mg Cd per kg leaf fresh weight (FW); 39.4 mg As per kg leaf dry weight (DW); 102.9 mg Cu per kg leaf DW and 10.92 g of Na per kg leaf DW. The levels of Cd are high when compared with the limits established by European regulations for leaf vegetables and fresh herbs (0.2 mg of Cd kg-1 FW [1]). Basil plants exposed to NaCl showed visible changes in their growth and development, but these changes are not sufficient to induce a rejection by the consumer because the plants still appear to be healthy. Plants contaminated with As also looked healthy throughout the experiment, although some visible differences could be detected comparing with the control. Plants contaminated with Cd and Cu, for more than 87 days, had high levels of Cd and Cu in the leaves but also presented visible chlorotic effects which could lead to a rejection by the consumer.