286 PLANT BIOCHEMISTRY 



is very slow. On ihe other hand, the methyl ester ol l-naphthaleneace- 

 tic acid (MENA) is used extensively since it is quite volatile, easily 

 applied in vapor form, and penetrates the tuber readily. Exposure 

 of potato tubers to vapors of MENA effectively prevents sprouting 

 for 1 year when the tubers are stored at temperatures between 50 and 

 60°F. In fact, sprout inhibition occurs at temperatures as high as 75°F. 

 for several months, although storage at this temperature results in 

 some shriveling. Although only very small amounts of MENA are 

 retained by the potato and most of this is in the skin, germination 

 of treated tubers is severely retarded. Most of the retarding effect 

 can be overcome if the potatoes are washed with soap and water before 

 planting. 



A considerable amount of work has been done relative to the 

 application of sprout-inhibiting substances directly to the plant in 

 the field. Foliar sprays of 2,4-D, MENA, lA, and NAA have all 

 resulted in significant decreases in the sprout growth of tubers which 

 were subsequently stored at 50°F. Foliar applications of maleic hydra- 

 zide prevent sprouting of potatoes subsequently stored for 8 months 

 at 57°F. In the latter case, there is an increased sucrose content and a 

 reduced loss of sucrose during storage. Both cooking quality and color 

 of potato chips have been improved by storage of the potatoes at such 

 a relatively high temperatine. 



Although the prevention of sprouting in onions by direct applica- 

 tion of growth regulators to the harvested bulbs has met with little 

 or no success, foliar sprays, prior to harvest, are quite promising. In 

 fact, marked success is reported from foliar sprays of maleic hydrazide 

 applied 2 weeks before harvesting. Under such conditions, onions 

 have been stored in perfect condition for at least 7 months. 



Root crops such as carrots, beets, turnips, and rutabagas respond to 

 postharvest treatment with MENA and NAA. Foliar application of 

 maleic hydrazide several days before harvest inhibits postharvest 

 sprouting of carrots, beets, parsnips, rutabagas, and turnips without 

 any reduction in crop yield. 



Abscission and Plant Regulators 



Abscission is the term used to describe the separation of an organ 

 or other plant part from the plant body. The dropping of fruit and 

 autumnal leaf-fall are classical examples of this process. Under normal 

 conditions abscission may be considered as a final process in a cycle of 

 growth processes. In fact, abscission serves a number of useful func- 

 tions in the survival of an individual plant or in the perpetuation of 

 the species. Among these functions should be mentioned the dispersal 



