Blue- and red-light regulation and circadian control of gene expression ofS-adenosylmethionine decarboxylase in Pharbitis nil

The abundance of mRNA for S-adenosylmethionine decarboxylase (SAMDC) (EC 4. 1.1.50) in leaves of Pharbitis nil is regulated by light. The level of this mRNA fluctuated dramatically, peaking 45 min after light exposure and then decreasing rapidly to a very low level. The half-life of the SAMDC mRNA wa s estimated by using actinomycin D to be approximately 30 min, which partly accounts for the rapid decline in the mRNA level after the peak of light i nduction is reached. The mRNA level for the SAMDC gene increased after ligh t exposure from red, green, blue or UV light, but not after far-red fight e xposure. The short irradiation of red light increased the expression of the SAMDC gene and this induction was reverted by subsequent far-red light irr adiation. The immediate blue light illumination after the Initial red light exposure resulted in a further increase in the SAMDC mRNA level. These res ults indicate that both the blue light photoreceptor- and phytochrome-media ted pathways are involved in the light regulation of the SAMDC gene. The tr anscription of the SAMDC gene was also shown to be under circadian control.