An Analysis of “Dark-osmotic Inhibition” of Germination of Lettuce Seeds

Abstract

Inhibition of lettuce (Lactuca sativa, var. Grand Rapids) seed germination in darkness at 21[degree]C by solutions of mannitol; sucrose; K, Na, and CaCl2; and Mg and Na2SO4 is approximately directly proportional to their osmotic pressures. Brief irradiation of the seeds with a small quantity of red light negates "dark-osmotic inhibition" (DOI), and the effect of red light can be reversed by sub-squently applied far red light. The term DOI is defined as the treatment given when one supplies darkness and an osmoticum and produces the end result of reduced percent germination. When germination has been inhibited osmotically for a sufficient period, most seeds do not germinate after transfer to water, and this should release a pure osmotic inhibition. Therefore, DOI operates in 2 phases, the primary phase being osmotic and the secondary, non-osmotic. DOI can be negated by the same factors that are known to nullify dark dormancy of lettuce seeds induced by high temperature (25 to 35[degree]C) treatments. It seems probable that DOI and perhaps other treatments that inhibit lettuce seed germination in darkness function primarily by delaying germination, and that during the delay a process occurs that causes permanent inhibition of germination in darkness.