430 



RADIATION BIOLOGY 



to determine some of the factors that govern their chlorophyll deficien- 

 cies. All the mutants examined produce protochlorophyll in the dark, 

 but in various quantities (Fig. 7-20; cf. Table 7-3). All the mutants but 

 one, white seedling-3, produce less protochlorophyll than does the normal 

 sib. A 5-min period of irradiation of the mutant seedlings converts their 

 protochlorophyll to chlorophyll a, and to about the same extent. But a 

 6-hr period of irradiation affects the chlorophyll content of the mutants 

 differently: it increases the chlorophyll content of the normal seedling 



12 - 



■5 10 



>. 



L. 

 T3 



cp 08 

 >v 



-♦- 

 c 

 <u 



6 



.? 006 

 a. 



o 



04 



0.02 



1 



PROTOCHLOROPHYLL 



D 



CHLOROPHYLL 



I 



< 



/. 



tLja 





ML 



Vi-v\ 



_fe[U 



NORMAL W3 g, V2 V4 V|2 I) 



Fig. 7-20. The transformation of protochlorophyll to chlorophyll a and the accumu- 

 lation or destruction of chlorophyll in various mutant strains of corn. The left-hand 

 rectangle of each set shows the protochlorophyll content of the dark-grown seedUngs; 

 the center rectangle shows the protochlorophyll (hatched) and the chlorophyll a 

 (unhatched) content after a 5-min illumination; the right-hand rectangle gives the 

 chlorophyll a content after a 6-hr illumination. (Koski, 1949.) 



about sixfold and of the mutants V2, Vi, ^12, and ij to lesser degrees, but it 

 decreases the chlorophyll content of gi slightly and of w^ almost to the 

 vanishing point. 



Thus examination of chlorophyll-deficient mutants has demonstrated 

 that chlorophyll deficiency is effected in two ways: by insufficient pro- 

 duction of chlorophyll precursor, protochlorophyll; and by heightened 

 chlorophyll destruction. 



A study of the chlorophyll mutants of barley by Highkin (1950) has 

 shown that a mutant (chlorina stock No. 2) can exist which contains no 

 chlorophyll b. This mutant grew to maturity and produced seed, but it 

 was not so vigorous as its normal sib. Eyster (1924) reported that he 

 had obtained chlorophyll mutants of corn which contained either only 

 chlorophyll a or chlorophyll b. Mutants of neither type matured. 



