1072 THE LIGHT FACTOR. I. INTENSITY CHAP. 28 



[IChU] 



(28.51A) <p = <Pi + {'Pi — <fi) 



Chlo 



The fluorescence yield light curves <p — f(Ia) are thus linear derivatives 

 of the function [ { Chi } ] = /(/«) . In practice, we use as independent vari- 

 able, the incident light intensity /; since we assume uniform light ab- 

 sorption (z. e., an optically thin system), we have (c/. equation 28.33) la — 

 fc*7Chlo. The relation of the fluorescence intensity curve F = f{Ia) to the 

 fluorescence yield curve <p — /(/„) is: 



(28.51B) F = ^h = <fj, + if, - ^i) 1'^^'^^!^=' 



Chlo 



(la = absorbed flux; F = emitted flux; I is measured in number of ein- 

 steins per sec. per cm.'^; Chlo in moles/liter.) 



It is easily possible to derive fluorescence yield curves for those of the 

 kinetic models discussed in section A7 in which light saturation is associated 

 with the slowness of a preparatory dark reaction (including in this definition 

 the reactions which restore the chloroph3dl complex after its photochemical 

 change) . 



We begin with the case in which strong light causes accumulation of 

 the chlorophyll complex in the carbon dioxide denuded form (such as 

 A-Chl-A'H20), or in the totafly reduced form (such as HX-Chl-HZ), be- 

 cause of slow rate of reaction of carbon dioxide (with the acceptor. A, or 

 with the reduced intermediate, HX). We can use here the simplest mech- 

 anism of this type (rather than the more elaborate mechanisms discussed 

 in chapter 27), namely: 



k*I 



(28.51Ca) ACO.-Chl-A'HzO > A-Chl-A'H.O + {OH} + {HCO2! 



+ H2O 



(28.51Cb) A • Chi • A'HoO + CO2 ^ ACO2 • Chi • A'HaO 



or: 



k*I 



(28.51Da) X- Chi -HZ > HX-Chl-HZ + [OH] 



+ H2O ^ ' 



(28.51Db) HX-Chl-HZ + CO2 — > jHCOo) + X- Chi -HZ 



The stationary concentration [{Chi}] (= [A-Chl-A'HaO] or fHX-- 

 Chl.HZ]) is: 



(28.51E) [{Chl}]= ^*'^Chlo 



k'lCO-i] + k*I 



For the light intensity at which the yield of fluorescence, <p, is equal to 

 the arithmetic mean of <pi and ^2 we obtain: 



(28.51F) /,I = ^'^^^''^ 



V^^ - k* 



