Tomato seeds pretreated with Antifreeze protein type I (AFP I) promotes the germination under cold stress by regulating the genes involved in germination process

This study was conducted to investigate the involvement of antifreeze proteins (AFPs; type I and III) in the germination mechanism of tomato seeds under low temperature stress. Germination of the seeds grown at a room temperature (25°C) was observed on 5 days after sowing (DAS), while all seeds exposed to a low temperature started to germinate at 16 days after sowing (DAS). However, in comparison with control seeds (0 µg/l), seeds treated with AFP I (100, 300, or 500 µg/l) germinated earlier and at a higher percentage until 20 DAS, and seeds treated with 100 µg/l AFP I showed the highest percentage of germination. Surprisingly, AFP III did not significantly increase germination, and the rate was lower among 500 µg/l AFP III-treated seeds compared with control seeds (0 µg/l). The transcription levels of the plasma membrane-associated H⁺-ATPase gene and antioxidant-related superoxide dismutase (SOD) and catalase 1 (CAT1) genes were analyzed, and the transcription levels of the genes in the seeds grown at 25°C were relatively low. For low temperature-treated seeds, H⁺-ATPase in control seeds (0 µg/l) was higher compared with that in AFP I-treated seeds and was lower compared with that in AFP III-treated seeds. The expression levels of the antioxidant-related genes (SOD and CAT1) were lower in AFP I-treated seeds than in control seeds (0 µg/l); however, they were higher in AFP III-treated seeds than in control seeds (0 µg/l). Overall, compared with AFP III, AFP I may potentially function as a cold-protective agent by modulating the genes associated with seed germination.