355 



David C. Fork 



X8) 



the blue regions of chlorophyll a absorption. Blinks^"'' has also 

 observed enhancement with combined blue and green wavelengths. 

 Enhancement, expressed as the ratio of the photosynthetic respKjnse 

 obtained when two beams are presented simultaneously divided by 

 the sum of their separate responses, is also given in figure 2 for 

 Porphvra in green and blue background light. Crvptopleura crista, 

 another intertidal red alga, showed a response (figure 3) similar 



c 

 o 



u 

 o 



■ 80 



40 



c 

 o 



J3 

 O 



c 

 o 



— I 1 1 



Cryptopleura crispa 



Thallus 



Wifh^o^-o-?-' A- 

 546m^i 

 supp. light ^ 



' -Without 



^ ^A supplementary 



light 



L 



01 — 

 400 



500 600 



Wavelength, rriM 



700 



Fig. 3. Action spectra for O2 production in Crvpto - 

 pleura crispa (15.5°C) with and without green (546 mp) 

 background light. Fork('\ 



to Porphvra when action spectra were determined without and with 

 green supplementary illumination absorbed by phycobilins. Drou - 

 etia rotata ^ a red alga growing exclusively in deep water where 

 red wavelengths are largely filtered out, was obtained at a depth 

 of 37 m. The thallus of this plant is too thick for ideal use 

 with polarographic techniques; nevertheless, it showed improved 

 chlorophyll activity when simultaneous phycobilin and chlorophyll 

 excitation was provided (figure 4). 



These action spectra for red algae demonstrate that the funda- 

 mental basis for the enhancement effect is not the pairing of low 

 energy quanta absorbed by chlorophyll a with higher energy quanta 

 absorbed by accessory pigments (or chlorophyll a itself), but 

 rather the requirement for dual excitation of accessory pigments 

 and chlorophyll a for efficient photosynthesis. Red and blue ab- 

 sorption by these algae is similar in that chlorophyll a excita- 

 tion is effected without appreciable phycobilin excitation. The 

 "inactive" chlorophyll of red algae could better be termed "unen- 

 hanced" chlorophyll. 



Enhancement spectra for a green and a brown marine alga, Ulva 

 and Endarachne respectively, are given in figure 5, Ulva showed 

 peaks of effectiveness around 485 and 645 mp corresponding most 

 closely to the absorption by chlorophyll b, while Endarachne 



