Germinating maize seeds with acetylcholine improves seedling heat tolerance

The increase in global temperature directly impacts the productive potential and morphological and physiological structures of maize ( Zea mays ). Acetylcholine (ACh) is an important bioregulator, produced in small amounts by the plant, that influences germination, reproduction, growth, development and cellular metabolic processes. This study evaluated the mitigating effects of ACh application (1, 10, 100, 1000 and 10000 μMol) on maize seeds germinated at high temperature, 37/25°C (day/night), compared with germination at 25/20°C. The application of ACh improved seedling development under heat stress, increasing root length (10, 100, 1000 and 10000 μMol ACh), root fresh mass (all doses), root dry mass (all doses), root:shoot ratio (1, 100, 1000 and 10000 μMol) and root surface area (1000 and 10000 μMol). Antioxidant enzyme activities (superoxide dismutase, catalase and peroxidase) increased, malondialdehyde content decreased and acetylcholinesterase (AChE) activity increased. Anatomical analysis of the coleoptile showed an increase in the distance between the center of the vascular bundle and the epidermis, thickness of the adaxial and abaxial epidermis, mesophyll thickness and the number of vascular bundles in response to ACh. Thus, ACh plays protective and growth-stimulatory roles, mitigating the effects of heat stress during maize germination and early development.