Nitrogen deficiency identifies carbon metabolism pathways and root adaptation in maize.

Sugars are essential for plant development, with nitrogen (N) availability playing a critical role in their distribution across plant organs, ultimately shaping growth patterns. However, the regulatory mechanisms modulating carbon (C) assimilate allocation and utilization under different N forms are not well understood. This study examined C fixation, utilization, and spatial re-distribution in the roots of hydroponically grown maize seedlings subjected to four N treatments: 1 mM NO(3) (-) (low N; LN), 2 mM NO(3) (-) (medium N; MN), 10 mM NO(3) (-) (high N; HN), and 1 mM NH(4) (+) (low ammonium; LA). LN treatment significantly increased soluble sugar, sucrose, and starch contents while promoting greater root biomass at the expense of shoot biomass, leading to a higher root to shoot assimilate allocation. The activities of sugar and starch metabolism enzymes were more tightly regulated under LN, indicating enhanced C utilization and increased competition for assimilates. Key genes involved in sugar (ZmSPS, ZmSuSy, ZmSWEET6, ZmSUC2, ZmSTP2, and ZmAINV1) and starch (ZmAGPASE and ZmSS) metabolism were upregulated under LN, correlating with increased root sucrose and starch accumulation and enhanced enzyme activity. Sucrose and starch accumulated predominantly in the brace and lateral roots. This pattern suggests that excess C accumulation results from inefficient C utilization in sink tissues rather than impaired C assimilation. These findings provide new insights into how LN modulates C partitioning in roots for stress adaptation, highlighting the importance of improving C utilization in sink tissues to mitigate N deficiency and enhance plant growth. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-025-01631-0.