Photosynthetic Action Spectra of Marine Algae

Abstract

A polarographic oxygen determination, with tissue in direct contact with a stationary platinum electrode, has been used to measure the photosynthetic response of marine algae. These were exposed to monochromatic light, of equal energy, at some 35 points through the visible spectrum (derived from a monochromator). Ulva and Monostroma (green algae) show action spectra which correspond very closely to their absorption spectra. Coilodesme (a brown alga) shows almost as good correspondence, including the spectral region absorbed by the carotenoid, fucoxanthin. In green and brown algae, light absorbed by both chlorophyll and carotenoids seems photosynthetically effective, although some inactive absorption by carotenoids is indicated. Action spectra for a wide variety of red algae, however, show marked deviations from their corresponding absorption spectra. The photosynthetic rates are high in the spectral regions absorbed by the water-soluble "phycobilin" pigments (phycoerythrin and phycocyanin), while the light absorbed by chlorophyll and carotenoids is poorly utilized for oxygen production. In red algae containing chiefly phycoerythrin, the action spectrum closely resembles that of the water-extracted pigment, with peaks corresponding to its absorption maxima (495, 540, and 565 mµ). Such algae include Delesseria, Schizymenia, and Porphyrella. In the genus Porphyra, there is a series P. nereocystis, P. naiadum, and P. perforata, with increasingly more phycocyanin and less phycoerythrin: the action spectra reflect this, with increasing activity in the orange-red region (600 to 640 mµ) where phycocyanin absorbs. In all these red algae, photosynthesis is almost minimal at 435 mµ and 675 mµ, where chlorophyll shows maximum absorption. Although the chlorophylls (and carotenoids) are present in quantities comparable to the green algae, their function is apparently not that of a primary light absorber; this role is taken over by the phycobilins. In this respect the red algae (Rhodophyta) appear unique among photosynthetic plants.

A tribute to Lawrence Rogers Blinks (1900–1989): light and algae

“…(From Haxo 2008, unpublished manuscript. ) The single most cited (293 times) of Blinks's many photosynthesis papers is that by Haxo and Blinks (1950) on red algae, which has been recognized by a wide variety of photosynthesis investigators in more than 36 reviews on photosynthesis and more than 200 published articles (not including the many textbooks on plant physiology that quote him) (ISI Web of Knowledge). A series of important evaluations of this work and that of Blinks in photosynthesis are given below.…”

“…It is widely acknowledged that the modern era was introduced by the work of Haxo and Blinks (1950). The latter workers showed that in red algae (Rhodophyta) the biliproteins acted largely as the lightharvesting pigment replacing chlorophyll in this role.…”

“…The action spectra of photosynthesis for a number of red algae were determined by Haxo and Blinks (1950), who showed that red monochromatic light absorbed primarily by chlorophyll was much less effective for photosynthesis than light absorbed by the accessory pigment, phycoerythrin. [Govindjee (pers.…”

“…Blinks's early membrane work laid the foundation for membrane transport in plant cells and electrical properties of membranes. He is best known in the photosynthesis community for the Haxo-Blinks oxygen electrode (Blinks and Skow 1938a, b, as modified and used in Haxo and Blinks 1950) and for the Blinks effect in a red alga Porphyra, where a green flash (540 nm) after red flash (675 nm) of light gave higher rates of oxygen exchange in contrast to a lower rate when the red flash was given after the green flash ); Blinks originally hypothesized (in hindsight, wrongly-editorial comment by Govindjee) that these red-green effects were due to respiration, not photosynthesis. Following the discovery of the ''red drop'' in photosynthetic yield (Emerson and Lewis 1943), Emerson et al (1957) discovered an enhancement effect in photosynthesis when two different light beams, exciting two different pigments, gave higher rates than the sum of photosynthesis in the two beams given separately (see Emerson and Rabinowitch 1960;.…”

“…(Also see comments on this in the section below where Francis Haxo's recollections, as well as comments by other scientists, are cited.) Haxo and Blinks (1950) had earlier found through measuring the action spectra of a number of red algae that light absorbed by phycoerythrin was far more effective in light harvesting for photosynthesis than light absorbed in the region of chlorophyll a. Duysens (1952) then discovered two forms of chlorophyll a, one fluorescent that received excitation energy from phycoerythrin, and the other that was non-fluorescent.…”