Effects of Low Nitrogen Stress on the Cell Structure and Chloroplast Proteome of Festuca arundinacea

Nitrogen is an essential nutrient for plant growth, development, and metabolism, and its deficiency can severely impact physiological functions and overall growth. This study aimed to investigate the effects of low nitrogen on the cell structure and chloroplast protein levels of tall fescue ( Festuca arundinacea ). The seedlings were subjected to low nitrogen stress, and the ultrastructures of their subcellular components were observed via transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The differential expression of chloroplast proteins under low-nitrogen stress was analyzed via quantitative proteomics via iTRAQ technology. The results revealed that the leaf cells presented pronounced protrusions and irregular surfaces, whereas normal mesophyll cell structures and intact chloroplasts were observed in the full-nitrogen group (nonstressed plants) of Festuca arundinacea . In contrast, leaf cells under low-nitrogen conditions appeared smoother and lacked protrusions, with mesophyll cells displaying necrosis or structural abnormalities and some membrane structures appearing blurred. Additionally, chloroplasts presented structural abnormalities, including the formation of oversized starch granules. Photosynthesis was inhibited under low-nitrogen conditions. A total of 441 differentially expressed chloroplast proteins were identified, with 177 upregulated and 264 downregulated. Notably, the expression of photosystem II core proteins and metabolic pathway synthases was downregulated, whereas the expression of certain antioxidant proteins was upregulated. These results indicate that low nitrogen stress disrupts the dynamic balance of the chloroplast proteome and inhibits photosynthetic efficiency. This study provides a theoretical foundation for optimizing nitrogen fertilization and improving stress resistance in turfgrass species.