Understanding the interplay between strigolactone and nitric oxide in alleviating cadmium-induced toxicity in Artemisia annua

Abstract

Metal stress severely limits the development and productivity of medicinal plants like A. annua. Strigolactone (SL), a relatively new plant hormone, and nitric oxide (NO) have demonstrated potential in mitigating HM-related symptoms in plants. Both SLs and NO are regulatory signals that play different roles under stressful conditions. At the moment, it is unclear how SLs and NO interact in plants under cadmium (Cd) stress. In this study, Artemisia annua was utilized to study the role and interaction of SL and NO for Cd stress tolerance. To investigate this, we undertook a detailed physiological, anatomical, and histochemical examination to determine the mechanisms by which SLs and NO reduce the effects of Cd stress on A. annua plants. Cadmium exposure hindered the growth of A. annua plants, influenced several chlorophyll fluorescence attributes, altered antioxidant enzyme activity, lowered cell viability, and caused lipid peroxidation, oxidative damage, and chloroplast ultrastructure abnormalities. A. annua plants grew better when treated with 4 μM synthetic SL analogue GR24 and 200 μM NO donor sodium nitroprusside. Meanwhile, under Cd stress, GR24 and/or SNP spray effectively boosted chlorophyll and carotenoid content, increased antioxidant enzyme activity, and elevated proline and glutathione levels. Treatment with SNP and/or GR24 improved chloroplast ultrastructure and chlorophyll fluorescence characteristics in plants under Cd-stress, resulting in better photosynthetic performance. It also reduced Cd accumulation, increased membrane permeability, and regulated stomatal behavior, resulting in enhanced stomatal conductance in Cd-stressed plants. The application of these growth regulators to plants under Cd-stress mitigated the decrease in glandular trichome dimensions and artemisinin content as observed from the HPLC results. Our results indicate that GR24 and NO, either individually or in combination, can be very effective in reducing Cd-induced damage in A. annua.