Early activation of antioxidant responses in Ni-stressed tomato cultivars determines their resilience under co-exposure to drought

Abstract

Throughout their life cycle, plants are subjected to a variety of environmental constraints, including abiotic stresses. The present study aimed at characterizing the responses of the two tomato cultivars Gold Nugget (GN) and Purple Calabash (PC) exposed to a combination of nickel (Ni) and drought. The following hypotheses were pursued: (i) the activation of responses to one stressor eases further adjustments to a second stressor; and (ii) the two tomato cultivars are differentially susceptible to drought and heavy metal-stress. Besides biometrical evaluations, the distribution of Ni in tissues and the redox homeostasis in both cultivars were compared in response to Ni-stress, polyethylene glycol (PEG)-induced drought, and to their combination. Regarding single stresses, Ni caused more harmful effects to plants than PEG-induced drought, in terms of growth inhibition and production of reactive oxygen species. Ni was mostly accumulated in the roots. The GN cultivar promptly activated antioxidant defenses under Ni-stress, while, in PC, such antioxidants were more strongly induced under combined stress. Stress co-exposure led to a drastic proline accumulation, resembling a signal of stress sensitivity. Overall, the GN cultivar seemed to be less susceptible to the combined stress than PC, as it could activate stronger antioxidant defenses under single Ni toxicity, possibly easing further adjustments demanded by the later co-exposure to drought. This study showed that the two cultivars of the same species had different levels of perception and responsiveness to Ni-induced stress, which translated into different susceptibilities to the combined exposure to PEG-induced drought.