Analysis of drought resistance of Malus hupehensis plants irradiated with 12C6+ heavy ion

Heavy ion radiation is widely used in radiation mutation breeding because it usually leads to a high mutation rate of irradiated materials. However, there is a scarcity of reports on heavy ion radiation's effects on apples. In this study, the seeds of Malus hupehensis irradiated by 12C6+ heavy ions were used as materials. Subsequently, the germinated plants underwent two brief drought treatments. The results revealed enhanced drought resistance in the irradiated plants, leading to the selection of four mutants (DR-1, DR-2, DR-3, and DR-27). Under prolonged drought treatment, these four mutant lines exhibited significantly lower stomatal density and higher POD activity than the control. Consequently, they suffered less damage while maintaining consistent growth and development, showcasing substantial drought resistance. Transcriptome analysis indicated higher expression levels of stress-responsive genes and pathways in DR-1 and DR-27 plants under prolonged drought stress compared to the control. Notably, within the starch and sucrose metabolic pathway, mutant plants displayed elevated sucrose synthase expression and significantly higher sucrose content than the control, indicating enhanced osmoregulation of mutants. Therefore, these results demonstrate that, under prolonged drought stress, mutant plants sustain growth and development by reducing stomatal density and boosting antioxidant enzyme activity and osmoregulation. We found that 12C6+ heavy ion radiation could enhance the drought resistance of Malus hupehensis plants, and the drought resistant plants which had been verified by long-term drought were selected from the irradiated plants, which provided a new theoretical and technical basis for 12C6+ heavy ion radiation breeding and was of great significance to the development of apple industry in arid areas.