CAROTENOIDS 



growth was also removed at the same time. So the extra carotenoid 

 formation might, as Wenzinger admits, also be due to failure of the 

 alga to synthesize chlorophyll in the absence of iron, the precursors 

 of chlorophyll being diverted into carotene production. It must be 

 admitted however, that in any case the experimental evidence provided 

 is by no means compelling. 



(ii) Mineral Constituents 



Haagi^o claims that in algae, a deficiency of magnesium sulphate 

 or of PO4' ' ' causes an accumulation of carotenoids before death 



supervenes. The following colour changes were noted, green > red 



y white (death). No supporting quantitative data were provided 



and, as in the case of fading leaves, the disappearance of chlorophylls 

 may only be unmasking the carotenoids already present. 



Fox and Sargent ^ ^ ^ found that the flagellate Dunaliella salina when 

 cultured in saturated saline (25 per cent.) produced only ^-carotene ; 

 in solutions \ to 2/3 saturated, much less (B-carotene was synthesized 

 and considerable amounts of chlorophyll made their appearance. 

 Spoehr and Milner, ^ ^ ^ jn an investigation not mainly concerned with 

 carotenoid metabolism, noted that in Chlorella pyrenoidosa there was a 

 decreasing carotenoid production with increasing '* R " values ; the 

 change was, however, much less marked than with chlorophyll. (The 

 " R " value measures the degree of reduction of the carbon tissues ; 

 see the original report for full details of the calculation of ** R.") 



As algae develop, the carotenoid content also increases ; this was 

 demonstrated in the case of plankton of the North Sea, principally 

 Rhizosolenia styliformis and Biddulphia sirensis. ^ ® ^ 



(iii) Action of Lights Temperature and Oxygen 



A survey of more recent work indicates that whilst light is not 

 essential for carotenoid production, it may have some qualitative effects. 



The absence of light does not prevent carotenoid production in 

 Polytoma uvella, Euglena gracilis, Astasia spp. ^'^ and Dictyococcus 

 cinnabarinus. ^ ' " 



Variations in the depth of water from which the algae were sampled 

 revealed only minor changes in their carotenoid content, i^** 2 09 

 Fritsch,"' however, states that the hpochromes of Treniepohlia normally 

 mask the green colour of the latter's chloroplasts, but that in shaded 

 situations these pigments may be almost completely lacking, so that 

 the growths appear green. 



Nitzschia closierium grown in " white " light (snow-white fluorescent 

 lamps) contained relatively less diadinoxanthin than did cultures 



140 



