Chitosan nanoparticles and germanium synergistically enhance photosynthetic efficiency, sugar metabolism, and anthocyanin biosynthesis via metabolic pathway modulation in guar

Boosting crop yield and quality is critical for feeding the world's population. The synergistic interaction of germanium (Ge) and chitosan nanoparticles (CSNPs) offers a novel approach to enhance guar (Cyamopsis tetragonoloba) yield and metabolism. This synergy led to substantial increases in guar biomass and yield, ranging from 33 % to 41 %, which correlated with improved photosynthesis. Improved photosynthesis induced sugar metabolism in leaves and seeds that directed to biosynthesis of primary metabolites including essential amino acids, organic acids (17.5–35.5 %), and lipids shifted toward unsaturated fatty acids. At the seed level, Ge and CSNPs significantly elevated crude protein, lipid, fiber, and sugar contents (r > 0.65–0.99). Anthocyanin levels in leaves increased significantly, reflecting efficient metabolic channeling and avoidance of bottlenecks in precursor accumulation (like phenylalanine) and enzymatic activity (e.g., UDP-glucose: flavonoid 3-O-glucosyltransferase saw a >4-fold increase). Furthermore, Ge + CSNPs boosted seed phosphorus by 27.9 % and antioxidant capacity by 57.4 %, which improved overall nutritional quality. Principal component analysis (71.65 % variance) confirmed that Ge + CSNPs coordinate metabolic changes, linking sugar availability and anthocyanin metabolism to increased guar yield. This study shows that Ge + CSNPs optimize metabolic transitions, offering a sustainable way to improve guar productivity, and nutritive values.