Carbon-Ion Irradiation Modulates Early Development of Lettuce Seedlings: A Morphotype-Specific Response

Understanding how plants respond to high-energy ionizing radiation is essential for developing resilient crops for controlled-environment agriculture and future space exploration. This study investigates whether carbon-ion (12C) irradiation of dry seeds can modulate early development in lettuce (Lactuca sativa L.) and induce dose-dependent responses relevant to controlled-environment agriculture and space farming. Dry seeds of red- and green-leaf morphotypes were exposed to increasing radiation doses (0.3, 1, 10, 20, and 25 Gy) and evaluated for germination, early growth, anatomical traits, and polyphenol content. While germination remained unaffected, seedling growth showed a hormetic response: low doses (0.3–1 Gy) promoted elongation of roots and hypocotyls, whereas higher doses (10–25 Gy) progressively inhibited growth. Anatomical changes in vascular traits and increased polyphenol levels at low doses indicated structural and metabolic adaptations enhancing early stress resistance. Notably, the two morphotypes responded differently: red-leaf lettuce exhibited stronger early vigor, higher biomass accumulation, and relatively greater anatomical stability, particularly at low to moderate doses, while the green-leaf type showed earlier and more pronounced growth inhibition, likely associated with differences in phenolic metabolism and resource allocation. These findings suggest that carbon-ion irradiation induces a hormetic response capable of boosting early vigor and triggering acclimatory processes in lettuce, with morphotype-specific differences underscoring its potential for optimizing crop performance in controlled environments and future extraterrestrial agriculture.