188 PLANT BIOCHEMISTRY 



any of them is lacking. A relationship between coniferin and lignin 

 has been suggested. Coniferin is a glucoside of coniferyl alcohol and 

 is isolated from the cambial sap of the spruce and other conifers. 



OCH3 

 HOCH2— CH=CH— ('v >— O— HC— C C G C— CH2OH 



coniferyl alcohol 



coniferin 



The free coniferyl alcohol has also been isolated from the sap of pine 

 species. This phenylpropyl structure has been suggested as the central 

 building unit. However, polymerizations of the above compound 

 cannot account for the high degree of cross-linking in lignin and the 

 stability to hydriodic acid. Involvement of such a unit does account 

 for the high vanillin yields on mild oxidation and for the compounds 

 isolated on alkali fusion. 



RESERVE MATERIALS 



Once formed, the structural materials discussed in the preceding sec- 

 tion are quite inert when considered from the metabolic standpoint. 

 Plants produce carbohydrates, lipides, or proteins which serve as 

 reserves during periods of energy surplus. Since plants, unlike animals, 

 provide their own food by way of the photosynthetic process, these 

 reserves are stored (1) in the active cell in amyloplasts, oil vacuoles, 

 (2) in special storage organs for the purpose of providing new vegeta- 

 tive growth, or (3) in the seed. 



Carbohydrates 



S/arc/i. The most abundant reserve carbohydrate in the plant world 

 is starch. Under favorable conditions it may be found in all the cells 

 of the living plant, usually in grains or granules. The two components 

 of starch, amylose and amylopectin (Chapter 3), vary in proportion 

 in different plants. Some plants produce predominantly amylose; 

 others accumulate a starch which is almost pure amylopectin. Table 

 8-2 lists the average distribution of the two components in some com- 

 mon starches. It will be noted from the table that not only does the 

 percentage distribution of the two components vary, but so does the 

 size of the molecule. The significance of these size differences to the 



