Timing of Selenium Application Modulates Antioxidant Performance and Nutrient Balance in Micro-tom Plants Under Cadmium Stress

Abstract

Cadmium (Cd) is a highly toxic heavy metal for plants. This contaminant is responsible for damaging the plant’s metabolism due to the overproduction of reactive oxygen species (ROS) and systemic oxidative stress. The selenium (Se) supply to plants exposed to this heavy metal is an efficient strategy to alleviate stress and lessen the adverse physiological outcomes of Cd exposure, by regulating the cellular redox homeostasis via antioxidant mechanisms. Although the biochemical responses of plants to Se application have been widely reported in the literature, there is no information available about the appropriate time to supply Se to improve the plant’s antioxidant system and restorage nutritional balance under Cd stress. Therefore, this study aimed to determine the most efficient timing of Se application to tomato plants exposed to Cd to improve their overall antioxidant responses performance. Micro-tom plants were submitted to 1 mM of CdCl2 and 1 μM of Na2SeO3 under different application regimes: the Se application before the Cd-induced stress; the simultaneous application of Se and Cd; the Se application after the Cd-induced stress; plants receiving only Se or Cd; and finally, the control plants receiving no Se/Cd. Overall, the results demonstrated that supplying Se before and during the contamination is more efficient in alleviating the stress compared to other approaches, by enhancing the activity of ROS-scavenging enzymes and other non-enzymatic antioxidant responses.