Annals of Botany

How large can a tomato grow? The answer lies in the cells

Plant growth is achieved by a combination of cell division and cell expansion. Cell expansion itself may be affected by DNA endo-reduplication, the replication of DNA, often several times, in the absence of cell division, which is usually correlated with large cell volumes. DNA endo-reduplication may thus be a way of achieving a large cell size. The relationships between these various processes may be complex, as illustrated by the work of Bertin (Avignon, France, pp. 439–447) on the growth of tomato fruit. In tomato, extensive DNA endo-reduplication occurs in the pericarp; some cells may undergo as many as seven rounds of DNA replication (starting in the diploid or 2C state) and thus contain 256C amounts of DNA. So, although division in the pericarp ceases relatively early, high biomass is achieved because of the large final size of the cells (which may be due in part to their high DNA content). The author has investigated the effects of a number of factors (of which we focus here on growth temperature), on cell division, cell expansion and DNA endo-reduplication in the growing fruit. Looking specifically at two of the growth temperature regimes (20/20 °C, day/night and 25/25 °C), it is clear that the relationship between division, expansion and endo-reduplication can be altered by temperature. Thus, at 20/20 °C, cell division in the pericarp continued for longer than at 25/25 °C, resulting in approx. 14 % more cells. However, because of a reduced period of cell expansion at 20/20 °C, final fruit volumes were not significantly different. Temperature also affected DNA endo-reduplication: plants at 25/25 °C reached a slightly higher mean DNA C-value than plants at 20/20 °C. Furthermore, the amount of DNA had a greater effect on cell volume at 25/25 °C than at 20/20 °C. This all reveals the complex interplay in the growth parameters that affect fruit size, a complexity well illustrated by the other data obtained in this very thorough investigation.