238 PLANT BIOCHEMISTRY 



as seed fungicides. Other organic fungicides, including formaldeliyde, 

 paraformaldehyde, chloranil, dichlone, phenols, and hexachloroben- 

 zene, have also been used. 



In general, fungicides have an inhibitory effect on enzyme action, 

 and most of the fungicidal agents exert an unfavorable effect on seed 

 germination. It is generally believed that a substance must enter 

 tissues in order to be toxic to an organism. There is evidence that a 

 number of fungicides penetrate seeds. Thus it has been found that 

 potatoes sprayed with Bordeaux mixture contain more copper within 

 the tuber than untreated potatoes. It has been noted that seeds with 

 damaged seed coats are more likely to be killed or inhibited after 

 treatment than the same variety with intact seed coats. 



In most cases fungicidal treatment of seeds seems to increase the 

 time needed for complete germination. The yields of agricultural 

 crops from treated seed are often depressed unless the seeding rate is 

 increased. It has been reported that certain seed treatments stimidate 

 the germination process, but usually the benefits derived from seed 

 treatment are due to control of organisms found either on the seed 

 or in the seed bed and not to stimulation of germination. 



METABOLISM OF GERMINATING SEEDS 



When seeds are placed in an environment favorable to germination, 

 the rate of metabolism is markedly accelerated. The reactions taking 

 place include hydrolysis, oxidation, desmolysis, and synthesis. Stored 

 food is changed from insoluble, immovable substances to soluble, 

 transportable compounds which are translocated. With these soluble 

 compounds as building blocks, the embryo can synthesize compounds 

 needed for the manufacture of new tissue. There is a great increase 

 in enzyme activity of seeds during germination. Carbohydrases, pro- 

 teinases, lipases, oxidases, and desmolases are active in germinating 

 seeds. 



Carbohydrate Metabolism 



The main storage carbohydrate of seeds is starch. The amy lose and 

 amylopectin components of starch are broken down by amylases or 

 by phosphorylase. The result of the hydrolysis of starch by amylases 

 is a mixture of glucose, maltose, and small dextrins. Maltase hy- 

 drolyzes the maltose to glucose. Low-molecular-weight dextrins are 

 also hydrolyzed to glucose, but the method by which this is accom- 



