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Physiological Study of Two Varieties of Ipomoea batatas

1925; University of Chicago Press; Volume: 80; Issue: 2 Linguagem: Inglês

10.1086/333521

1940-1205

George R. Johnstone,

Potato Plant Research

1. Freshly dug sweet potatoes, varieties Porto Rico and Triumph, increase in their rate of respiration apparently from the date of harvest until a maximum is reached, and then the rate gradually falls to a nearly constant level. 2. Cured sweet potatoes do not reach so high a maximum rate of respiration under the same conditions of storage and experimental procedure. 3. Curing decreases the rate of respiration. 4. Increase of respiration as a result of injury when the cortical layer is broken is largely due to facilitating the exchange of gases, rather than to direct wound stimulation. 5. Curing under carefully controlled conditions does not reduce the moisture content to any great extent. 6. Porto Rico variety has a larger percentage of carbon dioxide in the intercellular spaces than Triumph, under the same conditions of storage and treatment. 7. Respiration in both varieties responds to each 10⚬ rise in temperature in much the same way between 15⚬ and 35⚬ C., having nearly the same respiratory coefficients. The former variety respires at the greater rate. 8. Regeneration frequently occurs during the curing process, which indicates that dormancy depends on the existence of lower temperature, approximately 25⚬ C. and lower. 9. The hydrogen-ion concentrations of the expressed juices are about the same in each variety, being slightly acid. 10. Moisture and catalase activity are higher in Porto Rico variety than in Triumph. 11. Both laccase and peroxidase are present in Porto Rico variety. These enzymes seem to be important in connection with discoloration of the tissues on exposure to the air. 12. Laccase is thermostable at 60⚬-70⚬ C., while the organic peroxide of the peroxidase-oxidase system is thermolabile at 60⚬-65⚬ C. 13. The oxidase system seems to be injured by changes initiated by chilling. 14. Amylase activity varies considerably with storage conditions and treatment. Optimum activity occurs in a medium with a PH value of 7-9, with a marked falling off at PH 5. Amylolytic activity of Porto Rico is greater than that of Triumph. 15. Tests for tyrosinase were negative in each variety. 16. A physiological distinction of the two varieties is evident. Porto Rico has greater respiratory activity, greater enzymatic activity, and a higher moisture content.