CAROTENOIDS IN PLANTS 



grown in red light (neon tubes) ; the relative amounts of the other 

 xanthophylls produced were unchanged. ^ * ^ It was noted in the same 

 labotatory that Chlorella pyrenoidosa cultured in low intensity illumina- 

 tion contained more a- than p-carotene, whilst cultures produced 

 under high illumination reversed the situation. ^ ^ ^ 



Nothing is known of the effect of temperature on carotenogenesis 

 in algae. Oxygen appears to be necessary expecially for production of 

 xanthophylls, ^ ^ * but the evidence so far available is not compelling. 



FUNCTION OF CAROTENOIDS IN ALGAE 

 Photosynthesis 



It has previously been noted that in the higher plants carotenoids 

 do not take part directly in photosynthesis but act, if at all, by passing 

 on their absorbed energy to chlorophyll (see p. 86). The most recent 

 investigations indicate that the same situation exists in algae. 



The first investigations were carried out on Chlorella by Warburg 

 and Negelein. ^ ^ ^ They concluded that the carotenoids were used in 

 photosynthesis at very low efficiency. Montfort, i « '. i s s using brown 

 marine algae, Emerson and Lewis ^^^-^^^ using Chroococciis, Button 

 and Manning ^ ^ ^' ^ *"^ using Nitzschia closterium, and Wassink and 

 Kersten ^ ^ ' using Nitzschia spp. reached the same conclusions. 



Criticism has been levelled at the earlier work of Warburg and 

 Negelein ^ ^ * and of Montfort, ^ ^ ^ but there seems no doubt that the 

 situation has been accurately described by Button and Manning^^^ 

 and by Wassink and Kersten. ^ ^ ' 



Button and Manning found that, if photosynthesis produced by 

 irradiating the alga with light of wave-length 496 m[i is ascribed com- 

 pletely to chlorophyll, the situation arises that the quantum efficiency 

 of the process is over 100 per cent. ; thus the mediation of the carote- 

 noids was very strongly indicated. More recently these workers have 

 shown that this light absorbed by A^. closterium reappeared as chlorophyll 

 fluorescence. ^ * ^ Wassink and Kersten ^ ^ ' came to a similar conclusion 

 and also demonstrated that the energy is transferred to chlorophyll 

 without any wastage. They consider that a chlorophyll-fucoxanthin- 

 protein complex exists in the plant (See also Tanada^^^). 



Recently Blinks and his colleagues, 193-195 using Coilodesme spp. 

 have confirmed the positive but minor role played by carotenoids in 

 the photosynthetic processes in the brown algae and have extended 

 these observations to the green alga Ulva spp. The situation is, how- 

 ever, different in the case of the red algae : the light absorbed by carote- 

 noids, and indeed by chlorophylls, is not utilised for photosynthesis 



141 



