Foliar application of nano-silicon enhances drought tolerance rate of pot marigold (Calendula officinalis L.) by regulation of abscisic acid signaling

Pot marigold (Calendula officinalis L.) is an herbaceous ornamental and medicinal plant. Climate models predict a reduction of precipitations and increasing the average temperature. Therefore, agricultural plants will be more frequently exposed to water deficit stress. To investigate the influence of nano-silicon foliar application (0, 50, 100, and 200 mg L^{- 1}) on the alleviation of drought stress (100, 75, and 50% Field capacity (FC)) adverse effects on marigold plant characteristics, a factorial experiment was conducted based on a completely randomized design with three replications. The chlorophyll content of plants treated with nano-silicon 200 mg L^{- 1} decreased by 8.39% when drought stress increased from 100 to 50% FC. In line with electrolyte leakage percentage, the highest malondialdehyde and H₂O₂ content was measured in non-treated plants under a drought level of 50% FC. The activity of peroxidase and superoxide dismutase enzymes increased with increasing nano-silicon concentration and drought stress severity. Under all levels of nano-silicon treatment, the cell's abscisic acid content increased with increasing drought severity. Also, the highest abscisic acid content was measured in plants treated with nano-silicon 100 and 200 mg L^{- 1}. There was a significant negative correlation between electrolyte leakage, malondialdehyde and H₂O₂ content, and morphological characteristics, photosynthetic pigments content, total protein, and antioxidant enzymes activity. The positive effect of nano-silicon application is correlated with enhancing antioxidant enzymes activity, membrane stability, and cell osmotic potential. Also, one of the most critical mechanisms of silicon's effect on the alleviation of stress damage is the regulation of abscisic acid signaling. As a result, foliar application of nano-silicon could be introduced as a promising and influential technique to overcome the adverse effects of drought stress on morpho-physiological and biochemical characteristics of the marigold plant.