CAROTENOIDS 



covering the literature up to 1941-2 have been provided by Virtanen '° 

 and by Maynard and Beeson^^ 



The conclusions of the first workers in this field, Virtanen, von 

 Hansen, and Saastamoinen " "^ and Barnes, ' ^ have not been altered 

 significantly by results of more recent investigations. They found that 

 conditions which lead to the development of a healthy plant also favour 

 maximal carotenoid formation. Plants cultivated under normal 

 fertilizer conditions are not likely to be improved by addition of extra 

 fertilizers ; ' ?. « «, « a- h e reports to the contrary need rigid reinvestiga- 

 tion.**'"^^ Recently Virtanen '-^ =^ has stated that the more rapidly a 

 plant grows the greater its carotene concentration. 



Variations in the supply of fertilizers below the normal do un- 

 doubtedly adversely affect carotenoid production, s », 9 3- » 8 jj^ spite 

 of this nutritional variation Bernstein, Hamner and Parks"* suggest 

 that carotenoid formation depends " far more " on environment and 

 climatic factors than on the state of fertilization, for they found only 

 little variation in carotene content of plants grown in different soils 

 when the soils were contained in pots and subjected to identical environ- 

 mental conditions. This point of view is upheld by Janes, « ^ by Kem- 

 merer and Fraps, "" by Janes and Campbell, ^ '^ •^ and by Booth and 

 Dark, ^ ^ ^ but Beck and Redman ^ ° ^ consider any such environmental 

 relationship indirect. 



(ii) Nitrogen 



Under artificial conditions the type of nitrogen supplement is of 

 some importance. In sand cultures Virtanen et al.^^ consider that, in 

 general, potassium nitrate is a better source than ammonium sulphate, 

 but for pineapples"* and tobacco leaves ^°^ NH*4 is more effective 

 than NO' 3. Both claims may be true, for Mapson and Cruickshank ^ ** * 

 found that the presence of ammonium sulphate, ammonium chloride, 

 and ammonium phosphate decreased carotene production in cress 

 germinating on ashless filter paper by as much as 60 per cent., whilst 

 ammonium nitrate, ammonium bicarbonate, ammonium acetate, and 

 ammonium succinate had no such effect. The depressant action of 

 ammonium sulphate was reduced by sodium succinate, malate, or 

 aspartate but not by the free acids. These acids together with acetic and 

 nitric acids had no effect /)fr se on carotene synthesis. Most significantly 

 (NH4)2S04 did not inhibit synthesis of xanthophylls. NageP^ states 

 that when extra nitrogen in the form of NaNOg is fed to tobacco 

 plants there is an increase in the total carotenoid production but that, 

 at the same time, there is a decrease in the xanthophyll/carotene ratio, 

 indicating the preferential synthesis of carotenes. 



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