Drought stress differentially influences growth, physiology, and metabolite accumulation in Triticum aestivum (C3) and Amaranthus caudatus (C4) plants

Drought stress affects plant growth and production. To cope with drought stress, plants induced physiological and metabolic changes, serving as a protective approach under drought-stress conditions. The response to drought can vary based on plant type (C3 vs. C4) and the intensity of the stress. Therefore, here we aimed to investigate the different responses of wheat C3-Triticum aestivum and C4-Amaranthus caudatus plants to drought stress. To this end, the growth, photosynthetic parameters, oxidative stress, total antioxidant capacity, primary metabolites (amino acids and organic and fatty acids) and secondary metabolites (polyamines) were analyzed. Drought stress reduced growth, biomass, relative water content, water potential, and photosynthesis in both plants, with more severe effects observed in wheat. Drought-induced reduction in photosynthesis was linked to lower stomatal conductance, reduced photosynthetic enzyme activity, and decreased Fv/Fm, indicating impaired PSII function, effects that were more pronounced in wheat than in amaranth. This was accompanied by increased oxidative damage, as indicated by elevated levels of lipid peroxidation. To cope with drought stress, both plants accumulated metabolites involved in antioxidant defense and osmoregulation, including total antioxidant capacity, soluble sugars, proline, polyamines, organic acids, and fatty acids. This response was more pronounced in wheat, indicating its active deployment of defenses to cope with significant stress, in contrast to Amaranthus' greater physiological resilience.