312 Gene Action 



Chlorophyll 



Normal, green plants possess the green pigment, chlorophyll, so 

 necessary for their Ufe. Because of the presence of certain 

 genes, however, many plants have a smaller amount of chloro- 

 phyll pigment than is normal for individuals of that species. 

 There are several types of chlorophyll-deficient plants which 

 differ chiefly in the amount of chlorophyll present. Some nor- 

 mally green plants have no chlorophyll and live only a short 

 time. 



Other Plant Colors 



Colors other than chlorophyll have been studied in a number 

 of plants both genetically and chemically, and it has been shown 

 in some instances that a certain gene acts by producing a specific 

 chemical reaction. Such information is largely due to the w^ork 

 of Wheldale (Mrs. Onslow), Scott-Moncrieff (Mrs. Meares), and 

 Lawrence. These studies show that genes can control the pro- 

 duction of the yellow plastid pigments, of the soluble yellow 

 flavones, and of the anthocyanins, which produce the blue and 

 red colors so frequently found in plants. Other genes are known 

 which bring about the oxidation of pigments or cause differences 

 in the acidity of the cells where the pigments are found. As 

 the anthocyanins are indicator pigments, being red in the pres- 

 ence of acids and blue in the presence of bases, the pH of the 

 cell sap in which these pigments are dissolved is of importance 

 in determining their color. 



Lawrence, Scott-Moncrieff, and Sturgess have shown that in 

 hybrids between Streptocarpus Rexii (blue) and S. Dunnii (red), 

 seven types of flower color may be produced by the interaction 

 of four pairs of alleles. Chemical analyses of the flowers dem- 

 onstrate what particular anthocyanin pigments are present in 

 each flower type. Flowers homozygous for a have no antho- 

 cyanin and are ivory white. Anthocyanin pigment is produced 

 by the allele A. This anthocyanin is derived from the chemical 

 substance, pelargonidin, in the absence of genes R and 0. UK 

 is present, the anthocyanins are derived from cyanidin, whereas 

 if is present, they are derived from delphinidin. The pink 

 and salmon types are rr oo. Gene R adds one hydroxyl or meth- 

 oxyl group to the anthocyanin molecule and changes the color 



