Root cortical aerenchyma in rice improves organ-specific drought stress tolerance and antagonizes ethylene production

Drought is the major environmental factor damaging agriculture and plant development in susceptible areas. Rice is a major crop for food security and agricultural revenue, but the species is cultivated under flooded conditions, and the effects of water limitation on its root responses are still unclear. This work aimed to investigate water limitation impacts on rice’s root growth, aerenchyma development, anatomy of the cortical and vascular cylinder regions, and the capacity to produce ethylene from excised roots. Three rice genotypes (A502, Douradão, and Pampa) were grown under well-irrigated and water-stressed conditions for 50 days. At the end of the experiment, roots were sampled, and their growth parameters were analyzed. The cortical anatomy and vascular cylinder traits, along with the ethylene production of excised roots, were evaluated. Water stress reduced the root dry mass and the root: shoot ratio, and decreased the root tolerance index only from the Douradão genotype. Pampa and A502 showed higher root aerenchyma proportion compared to Douradão, and water stress increased the aerenchyma development only from A502 and Pampa genotypes. Excised roots from the Douradão genotype showed the highest ethylene production and Pampa the lowest, under drought. Cortical and vascular tissue structure from roots of rice genotypes indicates drought-tolerance traits. Higher aerenchyma development stands as an important tolerance trait and antagonizes ethylene production from excised rice roots.