Ivna Štolfa Čamagajevac

S-metolachlor promotes oxidative stress in green microalga Parachlorella kessleri - A potential environmental and health risk for higher organisms

The estimation of the toxic influences of herbicide products on non-target aquatic organisms is essential for evaluation of environmental contamination. We assessed the effects of the herbicide S-metolachlor (S-MET) on unicellular green microalga Parachlorella kessleri during 4-72 in vitro exposure to concentrations in the range 2-200μg/L. The results have shown that S-MET had a significant effect on algae, even in doses 10 and 20 times lower than the EC50 values obtained for P. kessleri (EC50-72h=1090μg/L). It generates reactive oxygen species in algae, decreases their growth and photosynthetic pigment concentration, changes their ultrastructure and alters the cellular antioxidant defence capacities. The levels of protein adducts with the reactive aldehyde 4-hydroxy-2-nonenal (HNE), the end-product of lipid peroxidation, were significantly elevated in S-MET treated cells revealing the insufficient effectiveness of P. kessleri antioxidant mechanisms and persistent lipid peroxidation. Since algae are fundamental aquatic food component, the damaged algal cells, still capable of dividing while having persistently increased content of HNE upon S-MET contamination could represent an important environmental toxic factor that might further affect higher organisms in the food chain.

Abiotic Stress Response in Plants: The Relevance of Tocopherols

In the natural environment, plants are continuously exposed to a variety of abiotic stresses yielding higher concentrations of reactive oxygen species (ROS), which may cause strong oxidation of cellular structures. To cope with oxidative stress plants have evolved very efficient antioxidant machinery, among which, lipophilic tocopherols represent an important nonenzymatic component. Tocopherol exists in four isomeric forms (α-, β-, γ-, δ-) and its composition depends on plant genotypic features and tissue type. It plays a crucial role together with other antioxidants (e.g., ascorbic acid, carotenoids, glutathione) in detoxifying ROS that emerge during stress conditions. As a component of thylakoid membranes, tocopherol acts as an important scavenger of singlet oxygen and other ROS thereby preventing lipid peroxidation and maintaining stable redox status in plant cells. In addition, tocopherols may protect the embryo from ROS during germination, under both aging and stress conditions. In this chapter, the role of tocopherols in the regulation of abiotic stress responses in plants will be emphasized.