ANNOUNCEMENTS
Sulfur (S) is an essential macronutrient that plays a crucial role in various physiological and biochemical processes in plants. This study delves into the morphological, physiological, biochemical, and molecular responses of different Brassica juncea genotypes when faced with sulfur deficiency, aiming to pinpoint traits linked to sulfur-use efficiency. The morphological analysis uncovered unique root responses among the genotypes, with Jaikisan displaying a more developed root system architecture, hinting at an adaptive strategy for nutrient uptake during sulfur stress. Biochemical tests showed notable decreases in chlorophyll and carotenoid levels, along with heightened oxidative stress (evidenced by increased H₂O₂ and MDA levels) and compromised membrane integrity across the genotypes under sulfur-deficient conditions. The VR genotype suffered the most severe stress symptoms, while the JR genotype managed to keep its pigment levels relatively stable and showed less oxidative damage, suggesting it has better tolerance and more efficient sulfur utilization. On a molecular level, histochemical GUS staining driven by the SULTR2;1 promoter revealed strong expression in the vascular tissues of roots, leaves, and reproductive structures, underscoring its vital role in systemic sulfate transport. Phylogenetic analysis of sulfate transporter genes indicated both evolutionary conservation and diversification, hinting at functional adaptations in Brassica juncea and its relatives. Promoter motif analysis uncovered a variety of overlapping cis-regulatory elements, suggesting a complex transcriptional regulation that responds to developmental signals and environmental stressors. A comparative sequence analysis between Arabidopsis thaliana and U-triangle Brassica species showed differences in SULTR2;1, likely reflecting adaptive evolution to meet diverse sulfur uptake needs. In summary, this study enhances our understanding of how Brassica juncea responds to sulfur stress, identifies promising genotypes and gene targets, and lays the groundwork for molecular breeding strategies aimed at boosting sulfur-use efficiency in crops.
KEYWORDS: Sulfur deficiency, Brassica juncea, sulfate transporters, Promoter motif analysis, Physiological and Biochemical Assays.
