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Plant and Cell Physiology, 1973, Vol. 14, No. 6 1081-1097
© 1973

Article

Photophosphorylation in intact algae: Effects of inhibitors, intensity of light, electron acceptor and donors

Glenn W. Bedell, II and Govindjee

Department of Botany, University of Illinois Urbana, Illinois 61801 U. S. A.

The luciferin-luciferase method was used to determine ATP extracted from darkmaintained and light-exposed samples of the green alga Chlorella pyrenoidosa and of the blue-green alga Anacystis nidulans. A few measurements on Synechococcus lividus (a bluegreen thermophile, clone 65°C) are also reported.

  1. The light-minus-dark ATP levels ({delta}ATP) from aerobic cells of Chlorella and Anacystis were negative; however, {delta}ATP from Synechococcus was positive. Large positive {delta}ATP was obtained in regularly grown (RG: moderate light) Chlorella treated with oligomycin; dark levels were reduced, light levels remained essentially unaffected. In high-light exposed (HLE) Chlorella, oligomycin reduced both light and dark ATP levels, but positive {delta} ATP was still obtained. However, in Anacystis, which has a different organization of thylakoid membrane, oligomycin severely reduced both the light and the dark ATP levels and the {delta}ATP remained negative.
  2. The oligomycin (12 µM) treated Chlorella and the untreated Anacystis and Synechococcus show the presence of cyclic photophosphorylation under conditions in which the non-cyclic electron flow from photosystem II to photosystem I is blocked by 10 µM 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU), or not allowed to operate by the absence of CO2. Cyclic photophosphorylation ranged from 10–30% of the maximum {delta}ATP in RG, to 40–50% in HLE Chlorella. In RG Chlorella, cyclic and non-cyclic (in the absence of DCMU) photophosphorylation ({delta}ATP) saturate at about 103 ergs cm–2 sec–1 and 104 ergs cm–2 sec–1 and 104 ergs cm–2 sec–1 red (>640 nm) light, respectively; a lag was observed in the light curve.
  3. In Chlorella, the addition of the photosystem I electron acceptor methyl viologen (MV; 1 mM) increased {delta}ATP by twofold. Further addition of DCMU (25 µm) reduced this to the level observed with DCMU alone. If 1 mM reduced dichlorophenol indophenol or phenazine methosulphate (DCPIPH2 or PMSH2, respectively) was added along with DCMU, the {delta}ATP level was 30–40% of the control. Further addition of MV increased the JATP to be 70–80% of that of the control. These and other results confirm the presence of both non-cyclic and cyclic photophosphorylation in vivo, the former predominating in Chlorella, and the latter in Anacystis and Synechococcus.

(Received May 1, 1973; )
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