Mycochrome system in the reversible photoinduction of conidiation in Helminthosporium oryzae, with special reference to intermittent photo stimuli

Abstract

Conidiophore formation in Helminthosporium oryzae V. Breda de Haan (ATCC 38851) was induced by near-ultraviolet radiation, and the conidia developed in subsequent darkness. With regard to repetitive near-ultraviolet light pulses, more fluence was needed to induce the same level of conidiation as that induced by continuous near-ultraviolet radiation. With a lengthening of the duration of the dark-intervals (50 ms to 10 s) between 50-ms light pulses, much more fluence was required. On the other hand, blue radiation applied just before near-ultraviolet radiation suppressed the induction of conidiation. When preirradiated with repetitive blue light pulses, the fluence needed to suppress induction of conidiation to the same level as that of continuous blue radiation was somewhat less than that for continuous blue radiation. The longer the dark-interval duration (50 ms to 10 s) between light pulses, the less the fluence of blue radiation required. These results indicate that not only the photoreaction but also the dark reaction was very important for the accumulation of photo stimuli for both the blue and the near-ultraviolet light responses; however, they were kinetically quite different from each other.