Photoinduction of Massive β-Carotene Accumulation by the Alga Dunaliella bardawil

Abstract

The massive accumulation of .beta.-carotene by the halotolerant microalga Dunaliella bardawil, in response to high light intensity andseveral other environmental factors, has been studied so far underdifferent sets of fixed conditions. To determine the kinetics andcharacteristics of the induction of .beta.-carotene accumulation,cells continuously grown under white light of approximately 27 microeinsteinsper square meter per second were exposed to light of approximately1650 microeinsteins per square meter per second. The exposed cellsaccumulate .beta.-carotene in two stages: the first stage, lastingfor 24 hours, starts shortly after exposure, whereas the second stageconcomitantly with onset of the stationary phase and persists untilthe cells collapse. Actinomycin D, chloramphenicol, or cycloheximideadded to low-illuminated cultures abolish the subsequent inductionof .beta.-carotene accumulation by high light intensity. These results,together with the early exponential kinetics of accumulation, pointto the role of gene activation in the process. In vivo labeling ofproteins and in vitro translation of poly(A)+ mRNA revealed severalpronounced differences between low-illuminated and high-illuminatedcells. A strongly light-induced protein of approximately 55 kilodaltons,as well as other light-induced proteins could possibly fulfill acarotenogenic function.