Salt Pretreatment-Mediated Alleviation of Boron Toxicity in Safflower Cultivars: Growth, Boron Accumulation, Photochemical Activities, Antioxidant Defense Response

The study aims to elucidate alleviant effects of boron (B) toxicity by salt pretreatment (SP) on growth response, phytoremediation capacity, photosynthesis, and defense mechanisms in two safflower cultivars (Carthamus tinctorius L.; Dincer and Remzibey-05). Eighteen-day-old plants were divided into two groups: SP (75 mM NaCl for 5 days) and/or B treatment (C, 2, 4, 6, and 8 mM B for 10 days). Depending on the applied B toxicity, B concentrations in roots and leaves of both cultivars, necrotic areas of leaves, ion leakage (RLR), and H2O2 synthesis increased, while shoot and root length as well as biomass, water, chlorophyll a+b, and carotenoid content decreased. In addition, chlorophyll a fluorescence results revealed that every stage of the light reactions of photosynthesis was adversely affected under B toxicity, resulting in decreases in performance indexes (PIABS and PITOT). However, the cultivars tended to induce the synthesis of anthocyanins and flavonoids and increase the activity of antioxidant enzymes (SOD, POD, APX, and GR) to detoxify reactive oxygen species (ROS) under B toxicity. SP mitigated the negative effects of toxic B on biomass, water and pigment content, membrane integrity, photosynthetic activity, and defense systems. Considering all results, Remzibey-05 was able to better overcome the biochemical and physiological changes that may be caused by B toxicity by more effectively rendering B harmless, although it accumulated more B than Dincer.