Phototransformation of the Red-Light-Absorbing Form to the Far-Red-Light-Absorbing Form of Phytochrome in Pea Epicotyl Tissue Measured by a Multichannel Transient Spectrum Analyser

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Phototransformation of the red-light-absorbing form (P_R) to the far-red-light-absorbing form (P_<FR>) of phytochrome in 7-day-old etiolated pea epicotyl hook segments was examined at 0.5℃ after a red laser flash excitation using a multichannel transient spectra analyser with electrically gated photomultiplier. Effects of a red laser pulse on the induction of phototransformation from P_R to P_<FR> Were saturated at ca. 15 mJ for flash wavelengths of both 640 and 655nm. The amount of P_<FR> induced by a saturating laser pulse was ca. 50% of that obtained at the photostationary equilibrium. A difference spectrum measured 15μs after the flash showed an absorbance increase at 697nm and a decrease at 663nm. A difference spectrum determined 200ms after the flash showed no such major absorbance increase. Kinetic analysis of the rapid absorbance decrease at 700 and 710nm gave one simple first-order reaction component having a rate constant of 2,500 s^<-1>. Kinetics of P_<FR> appearance measured by absorbance increase at 750nm was resolved into three first-order reactions having rate constants of 5, 1.8 and 0.4 s^<-1>. The second flash light of 710nm given 2μs and 2ms after the first red flash irradiation on P_R resulted in the formation of P_R rather than P_<FR>.
日本植物生理学会の論文