Photocontrol of chlorophyl and biliprotein synthesis in seaweeds: possible photoreceptors and ecological considerations
Félix López-Figueroa, Francisco Xavier Niell

The control ofchlorophyll (Chla) and biliprotein synthesis by light pulses and continuouslight of different qualities in a variety of seaweeds has been investigated.Chlorophyll synthesis was mainly stimulated by red light pulses in the red algaPorphyra umbilicalis. Because the effect of red light showed somefar-red reversibility, the involvement of phytochrome has been proposed. Theinduction of chlorophyll synthesis in the green alga Ulva rigida, in thered algae Corallina elongata, Plocamium cartilagineum and Schizymeniadubyi and in the brown alga Dictyota dichotoma was 1.5-5 timesgreater after blue light pulses than after red light pulses. This blue-lighteffect cannot be due to phytochrome because blue light produces a lower levelof active phytochrome, Pfr than red light. Thus, the involvement ofa specific blue-light photoreceptor is proposed. Furthermore, because theeffect of blue light was reversed by far-red light pulses the coaction betweena blue-light photoreceptor and phytochrome has been suggested. In Porphyra andCorallina, phycoerythrin (PE) synthesis was mainly stimulated by greenlight pulses. Phycocyanin (PC) synthesis, however, was induced by red lightpulses. Both red and green effects were partially reversed by far-red lightpulses. Thus, the involvement of phytochrome in the control of biliproteinsynthesis has also been proposed. Furthermore, because green light produce alower level of Pfr than red light, the involvement of a specificgreen-light photoreceptor in the control of PE synthesis was suggested. Algaewhich grow at greater depths (Corallina) presented a greater increase inthe ratios PE/Chla and PC/Chla in red, blue and green continuous light thanalgae growing in surface waters (Porphyra). The highest increase in bothratios was in green light. Thus, the pigment content could be adapted to deepcoastal water where green and orange light predominate. Two groups of algae inthe intertidal system studied were found to respond differently to artificial light:In the first group composed only of Porphyra growing under similar lightconditions to those of terrestrial plants, chlorophyll synthesis seemed to becontrolled solely by phytochrome. In the second group, algae growing at lowerdepths, chlorophyll synthesis seemed to be controlled by two photoreceptors,phytochrome and a blue-light photoreceptor. The blue effect on chlorophyllsynthesis increased in algae growing at shallower depths. These algae couldadapt their pigment content to the daily and yearly underwater light changesthrough two photoreceptor systems. Red:far-red (R:FR) and blue:red (B:R) ratiosdetected by the phytochrome and a blue-light photoreceptor could operate aslight intensity and light quality detectors as in higher plants.

Keywords: Biliprotein, Blue-light photoreceptor, Chlorophyll, Chlorophyta,Phaeophyta, Phytochrome, Rhodophyta, Seaweeds, Underwater light.
Contents of this volume Sci. Mar. 55(3) : 519-527 Back PDF
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