ROLES OF SOLUBLE SUGARS IN PROTECTING PHYTOCHROME-MEDIATED AND GIBBERELLIN-A(3)-MEDIATED GERMINATION CONTROL IN SKOTODORMANT LETTUCE SEEDS

Skotodormant seeds of Lactuca sativa Grand Rapids imbibed in darkness for 10 days (IO-day DS) germinated poorly upon terminal treatment with red light (R) or gibberellin A(3) (GA(3)). Soluble sugars in the imbi bition solutions influenced the depth of skotodormancy. Ten-day DS see ds, imbibed in 50-500 mM sucrose or 100-500 mM glucose and given termi nal GA(3) germinated completely and germinated about 80% when imbibed in 100 mM galactose, mannose, lactose, or maltose. In contrast, termin al R applied to 10-day DS seeds caused only 20-50% germination. If giv en R at day 0 and imbibed for 10 days in darkness in 500 mM sucrose or glucose, seeds washed free of exogenous glucose or sucrose then germi nated about 50% in darkness in water. These seeds responded to termina l R or GA(3) with complete germination. When seeds were given FR at da y 0, germination responses following terminal R or GA(3) were signific antly lower when the duration of DS was increased from 7-10 day DS to 15 days. In 10-day DS seeds given initial FR and imbibed in either sol utions of 50 or 100 mM sucrose and KNO3, either terminal R or GA(3) tr eatment gave complete or near complete germination. It is concluded th at seed exposure to certain soluble sugars and/or nitrate during a IO- day DS protected certain substrates and thereby extended the sensitivi ty of the seeds to terminal R or GA(3) treatment. The study provides s ubstantial evidence for nonhormonal factors associated with light and GA action in the control of seed skotodormancy.