Putrescine mitigates combined drought and nickel stress in Tanacetum balsamita L. through modulation of physiological and biochemical responses

Plants face significant challenges from abiotic stresses such as drought and heavy metal contamination, which damage their growth, physiological processes, and productivity. This study examines how exogenous putrescine application can reduce the combined effects of drought and nickel (Ni) stress in Tanacetum balsamita L., a medicinal plant with phytoremediation potential. Under controlled greenhouse conditions, plants experienced drought (50% field capacity), Ni contamination (0, 165, 220 mg kg⁻1 soil), and foliar putrescine (0.2 mM) treatments. Results showed that drought and Ni stress together reduced photosynthesis [Fv/Fm, Y(II)], chlorophyll, and biomass, and increased oxidative stress markers (H₂O₂, MDA) and antioxidant enzymes. Foliar application of putrescine alleviated stress by boosting photosynthesis, restoring chlorophyll content, reducing oxidative damage, decreasing Ni levels in shoots, increasing osmolytes such as proline and carbohydrates, and enhancing biomass and essential oil yield. The study shows that putrescine fortifies stress tolerance and phytoremediation potential in T. balsamita, aiding sustainable growth in Ni-contaminated, dry areas. These findings underscore the importance of polyamines in plant stress physiology and their potential for combating the effects of stressors.