Maize plants with low nitrogen tolerance were studied to see how they use nitrogen during the grain-filling stage. The researchers looked at two types of maize plants, one that is good at handling low nitrogen (ZD958) and one that is not (HN138). They found that ZD958 had higher grain yield and nitrogen utilization efficiency compared to HN138. ZD958 also showed better leaf nitrogen remobilization, photosynthetic rate, and nitrogen use efficiency. The enzymes responsible for nitrogen metabolism were more active in ZD958, which helped it grow better under low nitrogen conditions. This suggests that ZD958 has improved abilities to use nitrogen efficiently, leading to better grain weight and yield when nitrogen is limited.