Dual Action of White Light in the Photocontrol of Germination of Oryzopsis miliacea

Abstract

Spectral and kinetic analysis of light action showed that pro-motive effects of short irradiations with white light operated through the phytochrome system, the equilibrium favoring the promotive far-red absorbing form of the pigment (Pfr). Inhibitory effects of short irradiations with far-red light during the early hours of incubation acted on the dark-germinating fraction of the seed population, while promotive effects of later irradiations were acting on the remaining seeds, in which the red-absorbing form of the pigment (Pr) was gradually activated. This stimulating effect of far-red light is attributable to a probable absorption by Pr of part of the light transmitted by the far-red filters. Continuous irradiation with blue and far-red light prevented subsequent germination in darkness, while continuous irradiation with white light prevented germination only as long as it was applied, and caused promotion if followed by darkness. This promotion could be reversed by a short irradiation with far-red light, as well as by continuous white irradiation. Thus, presence of red in white light prevented the inhibition induced by its blue or far-red spectral regions, leaving most of the phytochrome system in the Pfr form, while presence of blue or far-red in the white light prevented the realization of the promotive action of Pfr. An additional pigment system seems to participate in the photocontrol of germination in this species, probably the "high-energy blue-far-red system.".