Long-term storage of dormant Grand Rapids lettuce seeds in the imbibed state: physiological and metabolic changes

Grand Rapids lettuce (Lactuca sativa L.) seeds retained their viability for up to ten months when maintained in the fully imbibed state on moist filter paper at 25°C in darkness. The ability of red light (R) to promote their germination was essentially lost within one week from the start of imbibition; sensitivity to gibberellic acid was retained for two weeks longer. Seeds which did not respond to either treatment had entered the state of secondary dormancy (skotodormancy). This could be relieved at all times by a combination of benzyladenine and R applied to the intact seed, or by isolation of the embryo and incubation on water. Protein synthesis increased initially following imbibition but declined after 72 h to a constant low level. Respiration declined over the first week of storage in the imbibed state to a much-reduced steady level. Cotyledonary lipid declined between four and ten months of storage but the axial lipid remained unchanged. Sucrose in the embryo increased after five months, but no changes in glucose, galactose, fructose or mannose were found. The total N content of the cotyledons declined over the first three months of storage in the imbibed state, with a concomitant rise in axial N; the latter declined slowly thereafter. Basal α-galactosidase (EC 3.2.1.22) activity decreased over seven months, but the phytochrome-induced component could not be raised by a 15-min R treatment even after one month. Germination induced by R and benzyladenine was achieved at later times without a rise in α-galactosidase levels.