The bluelight effect

The underwater light field in oceanic waters becomes, as we have seen earlier, predominantly blue-green and eventually blue with increasing depth. There is evidence for the existence of specific effects of blue light on the development of the photosynthetic apparatus of certain phyto-plankton species. Wallen and Geen (1971a, b) found that cells of the marine diatom Cyclotella nana grown in blue light (0.8 Wm~2) contained 20% more chlorophyll a and had a 70% higher light-saturated photosyn-thetic rate per cell than cells grown in white light at the same intensity. Jeffrey and Vesk (1977, 1978) observed that in cells of the marine diatom Stephanopyxis turris grown in blue-green light (4Wm-2), the cellular content of all the chloroplast pigments (chlorophylls a and c, fucoxanthin and other carotenoids) was about twice that in cells grown under the same intensity of white light (Fig. 12.9). Both the number of chloroplasts per cell and the number of three-thylakoid compound lamellae within each chloroplast were higher in the cells grown in blue-green light (Fig. 12.10). Furthermore, the blue-green-light-grown cells were better able to utilize low-intensity (the same irradiance as during growth) blue-green light for photosynthesis than the white-light-grown cells, achieving a 42% higher rate. Vesk and Jeffrey (1977) examined a number of other marine phyto-plankton species. Substantial increases in pigment content (55-146%) in blue-green-light-grown cells compared to white-light-grown (both at 4Wm-2) cells were observed in five diatom, one dinoflagellate and one cryptomonad species. Minor increases (17-39%) were found in two diatom, two dinoflagellate, one prymnesiophyte, one chrysophyte and

Fig. 12.9 Absorbance spectra of cells of the marine diatom Stephanopyxis turris grown in white (-) or blue-green ( ) light (4W m~2, in each case). (By permission, from Vesk and Jeffrey (1977), Journal ofPhycology, 13, 280-8.) The cells are suspended at a concentration of 200 000 cells ml_l.

Fig. 12.9 Absorbance spectra of cells of the marine diatom Stephanopyxis turris grown in white (-) or blue-green ( ) light (4W m~2, in each case). (By permission, from Vesk and Jeffrey (1977), Journal ofPhycology, 13, 280-8.) The cells are suspended at a concentration of 200 000 cells ml_l.

one chlorophyte species. There was no chlorophyll increase in two diatom and one prymnesiophyte species. Thus, the ability to increase pigment content in a blue-green light field is common, but not universal, among marine phytoplankton. There was little alteration in the proportions of the different photosynthetic pigments, and so these blue-light-induced changes are not examples of complementary chromatic adaptation. Evidence that the increases in pigment content were accompanied by increases in the number of thylakoids per chloroplast was obtained in a dinoflagellate and a cryptomonad, as well as certain diatom species: in some diatom species the number of chloroplasts also increased.626

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