Carbohydrate metabolism in Dioscorea esculenta (Lour.) Burk. tubers and Curcuma longa L. rhizomes during two phases of dormancy.

ABSTRACT

We have examined the changes in carbohydrate metabolism in food yam (Dioscorea esculenta (Lour.) Burk.) tubers and in an economically important spice cum medicinal plant turmeric (Curcuma longa L.) rhizomes under storage. Both specimens showed varied levels of dormancy and sprouting appeared at the end of dormant period. Harvested, fully matured tubers of yam and rhizomes of turmeric were stored in wooden boxes under the conditions of 28+/-2 degrees C temperature and 65-75% relative humidity (RH) in dark. The starch, sugars, enzymes of starch degradation, respiration, glycolysis, tricarboxylic acid (TCA) cycle and oxidative pentose phosphate pathway (PPP) were studied during 1-70 days after harvest (DAH). This investigation revealed that, the starch degradation and the enzymes involved, viz. alpha-amylases and starch phosphorylase showed a lower level of activity during early period of dormancy, while sugar content and enzymes of carbohydrate metabolism increased rapidly during sprouting. The isoenzymic profiles of alpha-amylases showed marked variations in these two phases. The key enzymes of glycolysis, TCA cycle and PPP, viz. aldolase, succinic dehydrogenase, malic dehydrogenase, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were increased even before the visible appearance of sprouting and their activities were at their maximum during sprouting. Based of the observations the dormancy period may be distinctly divided into peak period of rest and presprouting period.