Selenium mitigates boron toxicity in <i>Nicotiana tabacum</i> via altering root anatomy, accumulation of boron, biochemical and physiological aspects

There is limited knowledge regarding the reduction of boron(B)-induced stress/toxicity in <i>Nicotiana tabacum</i> caused by selenium (Se), particularly about the effects on root anatomy, photosynthetic functions, as well as antioxidative responses. This study aimed to evaluate the effect of Se on B toxicity and the related mechanisms. Various levels of boric acid were administered to the soil. Every B treatment consisted of two Se treatments, which included a control group and Se treatment. The findings of our study indicate that the presence of high B levels resulted in a reduction in the growth of roots, as well as in the areas of the cortical parenchyma (CP) and vascular cylinder (VC). This, in turn, affected the ratio of VC/CP, the dry weight of shoots, relative water content (RWC) of both leaves and roots and concentration of indole-3-acetic acid (IAA) in roots. Treatments also increased length of specific roots, shoot/root ratio, and levels of 1-aminocyclopropane-1-carboxylic acid (ACC) and abscisic acid (ABA) in roots. Se addition resulted in an increase in various plant growth parameters, including shoot/root ratio, relative water content (RWC), specific root length, VC and CP areas, total root area, and IAA/ACC and IAA/ABA ratios. Se enhanced structure of xylem, plant growth regulator IAA, and reduced ACC and ABA, which promote plant aging, hence promoting the growth in presence of B-induced stress. Se exhibited statistically significant alleviating effect on growth when applied at a concentration of 100 mg B kg⁻¹. However, it did not exhibit a significant alleviating effect at a concentration of 300 mg B kg⁻¹. Nevertheless, the administration of Se did not result in a decrease in the accumulation of plant tissue B. Net photosynthetic rates were not considerably affected by the presence of B or Se. Se did not appreciably ameliorate the oxidative damages induced by high B.