Light Inhibition of Nigella Germination: The Dependence of a High Irradiance Reaction on 720-nm Irradiance

Seeds of Nigella damascena L. germinated in darkness. Incandescent light inhibited germination, with greater inhibition occurring during the latter half of the 24-h imbibitional period. The inhibitory effects of incandescent radiation depended upon irradiance; inhibition of germination by a 12-h irradiation also exhibited a broad spectrum FR irradiance dependence. An action spectrum in the region of 650-740 nm revealed that 720-nm radiation was most inhibitory, suggesting that a HIR was operative. An action of P, evidenced by photoreversible control of germination following brief R and FR irradiations, was documented when temperature was shifted upward but not when temperature was held constant.