FUNCTION OF CAROTENOIDS IN PHANEROGAMS 



(iii) Phosphorus 



The position of phosphorus is well established ; variations in soil 

 phosphate levels have no direct effect on carotenoid production. •^■' '• 

 10 6-107 Wynd and Noggle ^ " *• ^ " • have attempted to correlate caro- 

 tenoid production in cereals with the various phosphorus fractions in 

 the soil. At the moment their results are equivocal and difficult to 

 interpret. 



(iv) Potassium 



There may be an optimum level of potassium fertilization required 

 for formation of carotenoids because it is claimed that deficiency 

 reduces,* *'^^'' a moderate addition improves/ '^ ^' ^ '^ * and an excessive 

 addition inhibits, s 2, s 9, 9 s, 1 1 1 pigment production ; it must be borne 

 in mind, however, that there are further reports which state that 

 potassium has no controlling effect. * ^' * ^' * ^ 



(v) Sulphur 



There is one report that sulphur deficiency reduces carotenoid 

 production. ' ' 



The discussion so far has been confined to leafy materials ; when 

 fruit is considered, very careful experiments have failed to reveal any 

 effect of wide variations in macronutrients on the carotene content of 

 tomatoes, ^ ^ * (but cf. Schupfan) ^ ^ '* although the effect on growth and 

 fruitfulness was marked. 



(vi) Micronutrients 



Detailed investigations by Lyon, Beeson and Ellis led to the con- 

 clusion that the following micronutrients play no part in controlling 

 carotene formation in tomatoes. Manganese, copper, zinc, molyb- 

 denum and iron. ^ ^ ^ Lo and Chen, ^ ^ ' however found that zinc but 

 not nickel increased the carotene content of tomatoes. 



In leafy material, and to a lesser degree in roots (carrots) reactions 

 to micronutrient deficiencies have in some cases been noted. However, 

 calcium, » s, 1 s manganese, » s, 1 1 6a molybdenum,^ ^ ^ and aluminium, ^ ^ ' 

 have no effect, although there is one report that, in general, calcium 

 deficiency in sand cultures reduces carotene synthesis. ^ ^ ' Opinion 

 is so far unanimous that magnesium deficiency decreases, ^^'^^'-^^'^ 

 and that addition of zinc, 1 1 «. 1 1 « -increases carotenoid production. 

 Recent work suggests that a magnesium-calcium balance is necessary 

 for the optimal production of plant pigments ; soya beans grown on a 

 medium containing excess calcium compared with magnesium produce 

 more carotenoids and less chlorophylls than do plants cultured under 

 normal conditions. The situation is reversed when magnesium is in 



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