Biochemical Adaptations of Zea mays L. to Abiotic Stress: A Focus on Drought, Salinity, and Heavy Metals.

Maize (Zea mays L.), one of the most significant cereal crops in the world, is very susceptible to abiotic stresses that include drought, salinity, and heavy metal toxicity, among others, all of which pose a risk to food and nutrition security in the face of climate change. These stresses disrupt cellular homeostasis, cause oxidative damage, inhibit photosynthesis, and eventually lower yield. This work is a synthesis of recent progress in knowledge of the biochemical, physiological, and molecular adaptation of maize to these conditions. The key processes involve reactive oxygen species (ROS) and hormone-mediated signaling circuits; a strong antioxidant response (SOD, CAT, APX, and AsA-GSH); osmolytes (proline, glycine, betaine, and soluble sugars); and metal detoxification (phytochelatin, metallothioneins, and transporter-mediated) pathways. Genotypic variation can affect the effectiveness of these responses, and tolerant cultivars have been shown to have better redox regulation, ion homeostasis, and stress memory. Emerging biotechnological interventions, especially CRISPR/Cas9 genome editing and molecular breeding, offer promising opportunities to accelerate the development of multi-stress-tolerant maize. Nevertheless, there are knowledge gaps in the understanding of combined stress responses, the role of epigenetic regulation, and the field-level translation of biochemical processes into yield stability. This review highlights the necessity to adopt integrative and systems-level solutions that can integrate the understanding of the molecular basis, breeding, and biotechnology to improve the resilience of maize, protect productivity, and sustain agriculture in light of increasing climate variability.