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T. T. Bannister and M. J. Vrooman 



We suggest that this curvature of the contours is associated with 

 a curvature of the illumination curve of photosynthesis — i.e., 

 with the approach to saturation. 



The suggested role of saturation is based on an analysis of 

 which only the main points can be given here. In this analysis, 

 it was assumed that the spill-over and separate package models -- 

 and in particular the rate equations 3 through 6 -- refer to the 

 photochemical production of an intermediate which is subsequently 

 converted into products by a dark reaction, which is limiting in 

 high illuminations. In this case, the observed rates of photo- 

 synthesis (P, , P , and P-jg) are non-linear, saturable functions 

 of the lightiproSortional rates (p^, p^, and p-^g) of intermediate 

 formation. The analysis showed that only a very slight curvature 

 of the illumination curves P^^Cl) and PgCl) is necessary to ex- 

 plain the observed curvatures of the E and D functions. Spe- 

 cifically, illumination curves which would deviate on the average, 

 by only .2.io of saturating rate from a straight line (over the 

 range from to l/3 of saturating rate) suffice to explain the 

 observed E and D functions. This small curvature of the illu- 

 mination curves could exist within the experimental error asso- 

 ciated with our apparently linear illumination curves. 



CONCLUSIONS 



The following results of our work would seem to be of some 

 interest. To begin with, our results appear to be the first to 

 establish the dependence of enhancement over a fairly wide range 

 of both short-wave and far-red illuminations. By expressing this 

 dependence in terms of E and D, functions of the rates (p-j_, P2) 

 relative to the rate of saturated photosynthesis, enhancement can 

 be unambiguously referred to ordinary illumination curves of 

 photosynthesis. This point is noteworthy because many earlier 

 works have given ratios, such as E, without statement of rates; 

 in such cases, it is impossible to assess the importance of res- 

 piratory and saturation effects. Our results emphasize also that 

 E and D are very different functions; E can be maximum only at 

 very low far-red illumination while D increases steadily up to 

 comparatively high illuminations. 



Secondly, our analytical formulations of the spill-over and 

 separate package models give a theoretical basis for quantitative 

 description of the parameters governing enhancement. Thus, the 

 coefficients a and b are the wavelength- dependent parameters of 

 enhancement which one should seek from action spectra. Unhappily, 

 both models lead to equivalent illumination dependences of 



