Plant growth-promoting Nocardia JTT02 enhances Biomass, glucosinolate metabolism, and bioactive potential of three Lepidium sativum cultivars

Lepidium sativum (garden cress) is a nutritionally valuable plant rich in proteins, dietary fiber, omega-3 fatty acids, vitamins, and essential phytochemicals, and has a history of use in traditional medicine. This study investigated the potential of a novel endophytic actinobacterium, Nocardia JTT02, isolated from Tribulus terrestris (Jazan region, KSA) to enhance the biofortification of three L. sativum cultivars (Haraz, Rajab, and Khider). Nocardia JTT02, a potent plant growth-promoting (PGP) endophyte, significantly improved the biomass and photosynthetic activity (including Rubisco) in all cultivars. This enhancement is attributed to JTT02's production of phytohormones like auxin and gibberellin. Moreover, the improved photosynthesis by JTT02 treatment resulted in elevated levels of primary metabolites, including organic acids, fatty acid and essential amino acids, which serve as precursors for glucosinolates and phenolics. Correspondingly, individuals glucosinoaltes (e.g., glucotropaeolin, benzaldehyde, benzyl cyanide, and benzyl thiocyanate) and total glucosinolate content were elevated. This also correlated with the bacteria's ability to produce amino acids, which are precursors for glucosinolate metabolism. Along with these increases, overall myrosinase activity and concentrations of glucosinolate hydrolysis products also significantly increased. Furthermore, the accumulation of antioxidant metabolites, including phenolic acids and flavonoids, was enhanced by JTT02, leading to increased antioxidant capacity as determined by FRAP, ABTS, and DPPH assays. The JTT02 boosted the accumulation of bioactive metabolites also increased antibacterial activity against various pathogen. These results suggest that Nocardia JTT02 is promising as a biofertilizer for improving the growth, nutritional value, and disease resistance of L. sativum.