Morphological, micromorphological, and proteomic mechanisms associated with aluminum tolerance in contrasting sugarcane genotypes

Aluminum (Al) toxicity limits sugarcane productivity in acidic soils, primarily impairing root development. Despite advances in the physiological characterization of this stress, studies integrating structural and proteomic responses at the early stages of Al exposure remain scarce. In this context, this study aimed to characterize morphological, micromorphological, and proteomic responses to elucidate the mechanisms associated with Al tolerance in two contrasting sugarcane genotypes: RB867515 (G15) and RB966928 (G28), under high Al toxicity conditions (221 µM AlCl₃) for 10 days in a hydroponic system. Morphological and micromorphological analyses by scanning electron microscopy (SEM) showed that Al predominantly affected the root system, reducing root growth and lateral root formation, with more severe structural alterations in G15. In contrast, G28 preserved root architecture under stress. Proteomic analysis identified 108 differentially accumulated proteins (DAPs) in the roots of genotype G15 and 102 in G28, of which 32 were shared between both. In G28, enrichment was observed in proteins associated with carbohydrate metabolism and energy generation, including pathways such as glycolysis/gluconeogenesis, the tricarboxylic acid (TCA) cycle, and pyruvate metabolism, as well as processes related to phenylpropanoid biosynthesis, lipid metabolism, and protein processing. In G15, DAP accumulation was mainly associated with amino acid, carbohydrate, and nucleotide metabolism, as well as translation and protein processing processes, particularly involving the endoplasmic reticulum. Protein–protein interaction network analysis identified molecular targets associated with Al tolerance. In G28, proteins with high clustering coefficients stood out, such as asparagine synthetase and S-adenosylmethionine synthase, along with highly connected proteins from carbon metabolism, such as dihydrolipoyl dehydrogenase, suggesting a central role in metabolic maintenance under stress. In G15, ribosomal proteins such as ribosomal protein L35A and 40S ribosomal protein SA showed high connectivity, together with aconitate hydratase, reflecting greater activation of structural processes. Overall, Al tolerance is associated with the maintenance of root integrity and efficient metabolic regulation, whereas sensitive genotypes exhibit greater structural disorganization and stress-related molecular responses. These results demonstrate that Al tolerance in sugarcane depends on maintaining root integrity and efficient reprogramming of energy and redox metabolism, enabling the identification of potential molecular markers for the selection of tolerant genotypes in breeding programs aimed at cultivation in acidic soils.