PHOTOBIOLOGIE DU MÉSOCOTYLE D'AVOINE-III. DOUBLE EFFET DE LA LUMIÈRE BLEUE

Abstract— Using excise sections of oat first-internodes, a dual effect of blue light can be demonstrated on elongation when the sections are first irradiated in distilled H₂O, then incubated with gibberellic acid (GA). At low light energies (230 ergs/cm² per sec, for 2 min), a pretreatment with blue light enhances the GA effect above the elongation it can produce in the dark. At high energies (650 ergs/cm²/sec for 45 min), the same wavelengths cause an inhibition of the GA-induced elongation. An action spectrum for the two effects show a maximum near 435 mμ in both cases. Neither light effect is visible when indoyl-3-acetic acid is used instead of GA. Several physiological effects distinguish the two blue effects. The promotive effect is most marked in the young regions of the mesocotyl, whereas the maximum inhibitive effect is located in slightly older tissues. Time-course experiments showed that the promotive effect is partly due to an extension of the duration of elongation. The inhibitory effect is only temporary and vanishes about 30 hr after the beginning of the experiment. The promotive effect of blue light resembles the effect of far-red light, but the former can be observed with gibberellins A₂, A₄, A₅, A₆ and A₇ which are practically inactive after an irradiation with far-red light. The inhibitory effect of blue light is different from the red-light effect as shown by the time-course experiments.