THE ROLES OF INORGANIC NITROGEN SALTS IN MAINTAINING PHYTOCHROME-MEDIATED AND GIBBERELLIN A(3)-MEDIATED GERMINATION CONTROL IN SKOTODORMANTLETTUCE SEEDS

Skotodormant seeds of Lactuca sativa Grand Rapids imbibed in darkness for 10 days (10-day DS) germinated poorly upon terminal treatment with red light (R) or gibberellin A(3) (GA(3)). Inorganic nitrogen salts i n the imbibition solutions reduced seed skotodormancy. Ten-day DS seed s, imbibed in 25 mM salt solutions followed by terminal R, germinated 99% if imbibed in NH4NO3, 70% if imbibed in KNO3 or NH4Cl, and 55% if imbibed in NaNO3. Seeds imbibed in higher salt concentrations germinat ed fully upon terminal R treatment. Seeds imbibed in 25 mM NH4Cl or in 50 mM NH4NO3 germinated completely upon GA(3) treatment, Osmotic effe cts of imbibition media accounted for only part of the effect, since s eeds imbibed in 50 mM CaCl2 or NaCl germinated poorly following R or G A(3) treatment. Seeds imbibed in 500 mM polyethylene glycol (PEG) 1000 or mannitol solutions for 10 days still exhibited skotodormancy. Trea tments of R or GA(3) did not stimulate germination in seeds imbibed in mannitol, but germination was complete if seeds were given 1-h acid i mmersion plus a water rinse before the terminal R or GA(3) treatment. Seeds imbibed in 50-500 mM PEG during 10-day DS germinated significant ly better in response to terminal R. Terminal GA(3) significantly impr oved germination only in seeds imbibed at 500 mM PEG. P-fr appeared to function in mannitol-imbibed seed only after an acid treatment. Seed exposure to inorganic nitrogen salts during the 10-day DS maintained s eed sensitivity to terminal R or GA(3) treatment. The depth of seed sk otodormancy was related to the availability of inorganic nitrogen and also involved the levels of P-fr or endogenous GA(3).