INFLUENCE OF ARTIFICIAL CHANGES OF CHLOROPHYLL CONTENT 12G9 



cultures with chlorophyll contents differing in the ratio of 4:1. As shown 

 by figure 32.4, the saturation yields of these two forms in fact differed 

 widely (by a factor of 3.4, which is only 15% smaller than the ratio of the 

 chlorophyll contents). 



Emerson's light curves conform closely to the prototype of figure 

 28.20(/). In this case the reduction of the chlorophyll content by three 

 c]uarters, l)rought about by iron deficiency, had the same effect on photo- 

 synthesis as would have been caused by removal of three fourths of all cells 

 from a nonchlorotic suspension. In other words, chlorotic Chlorella suspen- 

 sions, hke Willstatter and Stoll's chlorotic leaves, behaved as "normal" 

 leaves. However, since we have described above several cases in which the 



Chlorotic 



200 



RELATIVE LIGHT IMTENSITY 



Fig. 32.4. Light curves of two Chlorella suspensions with different content of 

 chlorophyll (after Emerson 1929). Double arrow indicates the "linear range." 



relation was different {aurea leaves, autumn leaves, shade leaves and etio- 

 lated leaves), we are bound to conclude (as we did once before) that the two 

 components of the photosynthetic apparatus — chlorophyll and the rate- 

 limiting catalyst — are not identical ; and that even if the ratio of their quan- 

 tities often has a tendency to remain constant, this gives us no right to con- 

 sider the tw^o components as associated in a proportion that remains con- 

 stant under all conditions. 



The three different relationships between [Chi] and P""*^- are again 

 compared in figure 32.5, where light curves A are those of Emerson's 

 normal and chlorotic Chlorella cells (P'"'^*- proportional to [Chi]), while 

 light curves B correspond to Willstatter and Stoll's green and yellow leaves 

 (•pmax. roughly independent of [Chi]), and light curves C to the umbro- 

 philic and heliophilic plants of Lubimenko (P'"^"- antiparallel with [Chi]). 



The dependence of P"''''' on temperature was found by Emerson to be 

 unaffected by changes in the chlorophyll content of Chlorella cells. This 

 result is different from Willstatter and Stoll's observations with aurea 



