Cell and Nuclear Size in Vicia faba Roots: changes during Germination and in Response to Levels of Ambient Water

Changes in cell and nuclear size were studied in roots of germinatingseeds of Vicia faba in order to answer the following questions:(1) When is growth of cells and nuclei initiated? (2) Is theratio, nucleus: cell size, constant over the first two to threecell cycles, i.e. are nuclear and cell growth closely coordinatedor can they vary independently of one another? Answers to thesequestions should contribute to our knowledge of the relationbetween cell and nuclear growth and the systems that regulategrowth of actively proliferating cells. The results show thatmean cell area increased very little during the first cell cycleand then decreased over the subsequent two to three cell cycles,i.e. until roots reached a steady state condition. Nuclei, onthe other hand, increased in size from 30 to 50 h after seedswere sown, i.e. when most nuclei were in S or G₂ The mean andthe range in nuclear volumes reached in the first two mitoticcycles during germination are maintained when root meristemsachieve a steady state condition. Thus nuclei maintain a constantmean size over the first few cycles, while cells decrease insize. As a, result of this difference, the ratio, nucleus: cellarea, increases over the few first cell cycles from 0·157to 0·222. The ratio increases in both interphase andprophase cells. Increases in size of cells and nuclei are notabsolutely coordinated; this suggests that nuclear and cellgrowth are, to some extent, regulated independently of eachother. Vicia faba L, broad bean, nuclear volume, cell area, root meristem, germination, water level