Enhancement in the Blue-Green Alga, Anacystis nidulans

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Abstract
Enhancement phenomena in photosynthesis of the blue -green algae, Anacystis nidulans, were examined by use of a Haxo electrode and 2 monochromatic light beams. Stable photosynthetic response required special conditions such as low oxygen concentration to minimize apparently inhibiting effects of the electrode reaction. In order to obtain linear response to light intensity careful attention was given to effects of light saturation and to the Kok effect. Action spectra on complimentary backgrounds, enhancement spectra, and absorption spectra were obtained for normally pigmented cells (W) and for cells (R) grown in red light to give depressed chlorophyll content. The use of complimentary backgrounds which gave maximum enhancement allowed identification of the action spectra with pigment systems 1 and 2. As in Chlorella, there were 2 spectral regions, lambdai and lambda2, distinguished by enhancement phenomena. The lambda 2 region (530-654 in W cells) was related to high phycocyanin absorption. The lambda1 region had 2 segments ( 654 m/x in W cells) and was related to high chlorophyll a and carotenoid absorption. R cells of low chlorophyll content had a lower activity of pigment system 1 as evidenced by a broader lambda2 region, increased enhancement for lambda,, and decreased enhancement for lambdai. Some of the phycocyanin in R cells appeared not to be active in either pigment system. No evidence was found which would clearly discriminate between the separate package and spillover models for enhancement.