Acquisition of germination capacity, photosensitivity, and desiccation tolerance in lettuce seeds

Summary Germination capacity, photosensitivity, and desiccation tolerance are important attributes that seeds acquire during their development. Exploring the timing of the acquisition of these characteristics is important to better understand how different environmental conditions affecting the mother plant influence seed quality. Lettuce (Lactuca sativa L. cv. ‘Tango’) seeds were produced in the greenhouse. Seed germination under light and darkness was evaluated in fresh and desiccated seeds at 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 25, and 31 days after flowering (DAF). Seeds were desiccated ≈ 1 hour after harvest by placing them at 25°C and 57% RH. Seeds achieved maximum dry weight (physiological maturity, PM) at 13 DAF. In fresh seeds, 100% germination was observed 7 DAF. Onset of desiccation tolerance occurred 9 DAF, shortly after seed abscisic acid (ABA) concentration was at its highest level and coincident with the presence of abundant oil bodies in cotyledonary cells. Dark germination of fresh seeds increased from 0% at 11 DAF to 86% at 17 DAF and then decreased to less than 20% at 21 DAF. In general, desiccated seeds had lower dark germination percentages than fresh seeds. Onset of lettuce seed photosensitivity during the maturation desiccation phase was coincident with a sharp loss of seed water content from 37 to 11% between 17 and 19 DAF. These results support the involvement of ABA in storage reserve deposition and acquisition of desiccation tolerance during lettuce seed development and suggest that changes in seed water content during the maturation desiccation phase are associated with the onset of light requirement for lettuce seed germination.