Alleviation of the adverse effects of low atmospheric pressure stress by putrescine in Matricaria chamomilla

BACKGROUND: This study investigated the effects of low atmospheric pressure (hypobaric stress) and exogenous putrescine on physiological, biochemical, and molecular responses of Matricaria chamomilla seedlings. Plants were exposed to hypobaric stress (200 mbar), putrescine treatment (0, 0.1, 0.2, 0.4, and 0.8 mmol L⁻¹), and their combination for 2, 3, and 4 weeks to evaluate potential stress mitigation mechanisms. RESULTS: Hypobaric stress significantly reduced growth parameters and antioxidant capacity, which was accompanied by decreased flavonoid and phenolic contents as well as downregulation of chalcone synthase (CHS) and flavone synthase II (FNSII) expression. Elevated hydrogen peroxide (H₂O₂) levels under low-pressure conditions were associated with growth inhibition and oxidative imbalance. In contrast, putrescine treatment improved biomass accumulation, enhanced antioxidant enzyme activities, increased nitric oxide (NO) levels, and reduced H₂O₂ accumulation. Putrescine also partially restored phenolic and flavonoid contents. A positive correlation was observed between increased NO levels, enhanced antioxidant capacity, and improved growth, suggesting that increased NO levels are associated with improved antioxidant responses and may contribute to putrescine-related stress mitigation. Notably, application of putrescine treatment under hypobaric stress resulted in the most pronounced improvement in physiological performance, antioxidant status, secondary metabolite accumulation, and upregulation of CHS and FNSII transcript levels. CONCLUSION: These findings indicate that putrescine application is associated with improved tolerance of M. chamomilla seedlings to hypobaric stress, potentially through modulation of redox balance and activation of the flavonoid biosynthetic pathway. The responses appear to involve coordinated redox-related signaling processes rather than a single causal pathway. This study contributes to understanding plant adaptive mechanisms to low-pressure environments and provides physiological insights relevant to controlled low-pressure cultivation systems, such as those proposed for bioregenerative life-support applications.