Correlation of cell division and cell expansion to potato microtuber growth in vitro

The sink capacity of plant storage organs influences crop economic yield and relates to the number and volume of their cells. To obtain a better understanding of their contributions to the growth of potato microtubers produced in vitro, the number and volume of the cells in the tuber tissues were measured as tubers grew. Two potato cultivars, E-Potato 1 and Mira were employed and the results showed that cortex, perimedulla and pith tissue contributed for about 30, over 65 and up to 3% to the volume of the mature microtuber, respectively. The number of cells and cell volume increased simultaneously as the microtubers grew and the relationships could be described by a power function, Y = aW^b. However, the rate of cell division was greater than the rate of cell expansion and the former contributed more than the latter to the increase in tuber size. The rate of cell division was greatest in the cortex and least in the pith, but, because the perimedulla forms the largest part of the tuber, cell division in this tissue was particularly important. The regulation of cell division to improve the production of usable microtubers is discussed.