1959 Volume 72 Issue 850 Pages 137-145
The flower inhibitory effect of low intensity light preceding the dark period of adequate length (16 hours) was investigated in Pharbitis seedlings.
1) Eight hour incandescent light of 10lux inhibits flower formation.
2) The incandescent light of 10-25lux given for 8 hours suppresses the inductive effect of the following dark period entirely, and even that of 1000lux is not strong enough to bring about maximum photoperiodic response.
3) Spectral sensitivity of the low intensity light for flower inhibition was studied. Far-red light has the highest inhibitory effect and red light the lowest.
4) Daylight fluorescent light of 10lux which comprises little far-red light inhibits flowering far less than the incandescent light of the same intensity.
5) The daylight fluorescent light of 10lux mixed with the far-red light of 120 erg/cm2./sec. inhibits flowering remarkably when given for 8 hours.
6) Flower inhibitory effect of the incandescent light of 10lux is reversed by red light applied just before the dark period. But the red light mixed with the far-red light has little reversing effect for the flower inhibitory effect of the incandescent light.
Flower inhibitory effect of the incandescent light is attributable to the action of the far-red light comprised in it. “Red-far-red absorbing pigment system” is supposed to play an important role in the reaction preceding inductive dark period.