Ultraviolet Irradiation on a Coccoid Blue-green Alga: Survival, Photosynthesis, and Photoreactivation'

The effects of UV irradiation (254 m,u) on a cocooid blue-green alga Agmenellum quadruplicatum, Strain PR-6, have been examined in terms of the survival curve and measurement of short time photosynthetic rates. From study of survival evidence has been found for a strong photoreaotivation centered near 430 m/4&. Measurements of photosynthetic rate suggest that there is a correlation between decay of photosyn.thesis and survival after UV exposure. The IV induced decay in photosynthetic activity is reversed by the identical photoreactivation conditions that increase the survival level. The photosynthetic d-ata are interpreted as demonstrating a photoreactivation of photosynthesis in blue-green algae. The effects of radiation in the 220 to 300 m,l range on blue-green algae are not well known. Halldal (3) has noted the effects of UV irradiation on photosynthesis in Anabaena sp. Several reports have appeared comparing characteristics of ultraviolet resistan,t and wild-type strains of blue-green algae (7,12). Photoreactivation of UV damage of the blue-green algal virus LPP-1 within the host cell has been described (18). Evidence has also been presented that Plectonema boryanum contains photoreactivating enzyme when tested in the Hemophilus influenzae transformation assay (17). The present report deals with the nature of survival and photosynthesis in Agmenellum quadruplicatum, Strain PR-6, a coccoid blue-green alga after ultraviolet irradiation (254 mju). Both the survival level and the decay in photosynthesis after UV exposure are markedly influenced by a photoreactivation. An abstract of an early part of this work has previouslv appeared (14). Materials and Methods Agmnenellum quadruplicatum, Strain PR-6, hereinafter referred to as PR-6, is an isolate of this lab. It was routinely grown batch-wise in liquid culture using the test tube culture method of Myers (8) at 390 with 1 % CO2-in-air continuously bubbled through the tuibes. Illumination was provided by four 30 w cool white HO fluorescent lamps (two on each side) 7.5 cm from the tubes. At harvest the cell volume was approximately 1 mm3/ml. Chlorella pyrenoidosa (Emerson strain) was similarly grown but on Knop's medium at 250 (10). 1 This investigation was supported by National Science Foundation Grant GB 4721X. Suspensions used for UV irradiation and measurement of photosynthesis were handled in the same manner as for PR-6. In the plating experiments with PR-6 the test tube culture baths were modified to hold 10 Corning flasks (No. 5100, 125 ml). A 15 ml base layer of medium containing 1 % Difco agar 0140, was placed in the flask. A 0.1 ml aliquot of the cell suspension containing 100 to 300 cells was placed on the agar surface, then 1 ml of agarized medium at 44° was added and mixed with the suspension. Illumination was provided by a linear band of seven 60 w tungsten bulbs 15 cm from the flasks., The flasks were incubated at 390 with CO2 supplied by diffusion. The medium for both flask and liquid growth was slightly modified ASP-2 (16) containing 2 jug/l vitamin B12. A more complete discussion of the factors involved in the quantitative single-cell plating of coccoid blue-green algae has been published (16). To make the cell suspension used for measuring survival or photosynthesis, an exponentially growing culture of PR-6 was centrifuged, resuspended in fresh growth medium and diluted to approximately 1 X 107 cells/ml. Six ml of cell suspension was placed in an open petri dish (50 mm) and irradiated at a distance of 48 cm from a GE G15T8 lamp. In order to make all the UV dosages as equivalent as possible, all doses were given as a 1 min exposure period 1(17.5 ergs mm-2 sec-1) with a 10 to 15 sec intervening dark period, until the total dose desired had been reached. Thus, continuous irradiation periods greater than 1 min were interrupted in the same fashion as irradiation periods in which samples were periodically removed. The suspension was continuously stirred during the irradiation period. To prevent photoreactivation effects all operations were done under a safelight consisting of a tungsten lamp covered by Rohm and Haas Plexiglas, transparent colored sheet No. 2422, 0.125 inch thick. 1689 www.plantphysiol.org on September 22, 2017 Published by Downloaded from Copyright © 1968 American Society of Plant Biologists. All rights reserved.