EXPLORING THE ROLE OF PLANT HORMONES IN ROOT DEVELOPMENT UNDER LOW OXYGEN CONDITIONS: NEW INSIGHTS FOR CROP IMPROVEMENT

Abstract

Flooding-induced hypoxia represents a major constraint on crop productivity by impairing root growth and function. In this study, we investigated the hormonal and molecular mechanisms underlying root adaptation to low-oxygen stress in Arabidopsis thaliana and Oryza sativa using controlled hydroponic treatments (2% vs. 21% O₂), comprehensive hormone profiling, gene expression analysis, and detailed root architectural assessments. Under hypoxia, roots accumulated significantly higher levels of ethylene (2.5–2.8-fold increase) and abscisic acid (1.6–1.8-fold increase) alongside elevated gibberellins, cytokinins, and nitric oxide, while indole-3-acetic acid declined by ~30% relative to normoxic controls. Reactive oxygen species and antioxidant enzyme activities (SOD, CAT) were markedly enhanced, indicating a dual role for ROS in stress signaling and defense. Transcriptomic assays revealed robust upregulation of hormone-responsive genes (ARF1, ACS2, NCED5, PYL4), which emerged as central hubs in an integrated hormone-signaling network. Morphologically, hypoxia reduced primary root elongation by over 35%, decreased lateral root numbers, and promoted aerenchyma formation (up to 40% porosity) and adventitious rooting, thereby enhancing internal oxygen diffusion and water uptake. These coordinated hormonal, molecular, and structural responses underscore a complex crosstalk that reprograms root development towards survival under oxygen deprivation. Our findings identify key regulatory nodes—particularly at the intersection of ethylene biosynthesis and auxin–ABA signaling—that offer promising targets for genetic or chemical modulation. By translating these insights into crop breeding and management practices, including genome editing and hormone analog applications, it will be possible to develop flood-tolerant cultivars and optimize agronomic interventions for waterlogged soils. This work lays a foundation for sustainable crop improvement strategies aimed at stabilizing yields in flood-prone environments.