Carbohydrate metabolism in Nerine sarniensis bulbs developing in liquid culture

Anatomical and physiological changes accompanying enhanced Nerine sarniensi s cv. Salmon Supreme bulb growth in vitro were examined. Small bulbs, 2-3 m m in diameter, grown in vitro on a semi-solid medium were subcultured to li quid medium with elevated levels of sucrose (Suc) and inorganic phosphate, Bulbs' fresh and drg weights, carbohydrate contents and the activities of e nzymes related to carbohydrate metabolism were determined at different stag es of bulb development. Starch was the dominant storage carbohydrate in the se bulbs, and the leaf bases parenchyma cells were the principal storage ti ssue. During the first month of bulb growth, only small changes in starch c ontent were detected, However, an increase in starch level was observed at later stages of development, The activity of ADP-glucose pyrophosphorylase (EC 2.7.7.27), a key enzyme of starch synthesis, increased just before the increase in starch accumulation. Sucrose was the dominant soluble sugar in the bulbs, only traces of glucose and fructose were detected. The activity of alkaline invertase (INV, EC 3.2.1.26) was higher than that of acid INV d uring the growth period, Sucrose synthase (EC 2.4.1.13) exhibited the highe st Sue-degrading activity during bulb growth, Suc was hydrolyzed in the med ium by the cell wall bound acid INV during the growing period. The results are discussed in relation to enhanced nerine bulb growth and development in vitro.