1998 Volume 67 Issue 2 Pages 200-207
The plastid-amyloplast system involved in starch synthesis and accumulation in Eddoe corm was observed by electron microscopes.According to an observation with a scanning electron microscope, a large number of plastids were elongating and replicating in parenchyma cells at the early stage of the corm enlargement.While the corm enlarged, plastids accumulated starch grains and then developed into amyloplasts.The amyloplasts grew large wholly as a result of partial enlargement.In the enlarging part of the amyloplast, smaller, rounder polygonal-shaped starch grains were gathered together.At the harvest stage, many amyloplasts were about 20 μm in diameter.The largest amyloplast, 40 μm in diameter, contained about 4, 000 starch grains with diameters of 1∼3 μm. According to an observation with a transmission electron microscope, the plastid formed a "starch-area"which consisted of starch grains and an electron-lucent part surrounding each grain as a result of starch accumulation.The amyloplasts had stroma in their restricted peripheral space, and kept forming starch grains in the stroma until harvest time.From these observation, we suggest that the site synthesizing starch molecules and developing starch grains is the electron-lucent space surrounding each grain throughout development.It was made clear that a number of starch grains in an amyloplast are developed continuously in the restricted peripheral stroma from the early stage to harvest time.
