Koch, G., Dambreville, A., Rolland, G., Bertin, N., Granier, C.
Robust relationships between organ size and their cell number have been reported for different plant species and many environmental scenarios, suggesting that a large part of plant development plasticity is related to changes in cell cycle activity. Endoreduplication is a variant of the cell cycle during which DNA replication occurs without mitosis. The role of endoreduplication in plant functioning is not yet fully elucidated. However, it results in the multiplication of nuclear ploidy and interacts with cell growth as a positive correlation is often reported between cellular ploidy and cell area. The functional links between cell division, cell expansion and endoreduplication during organ development remain unclear. The relative contribution of these three processes to the final size of plant organs has been considered only in a few studies, for instance on tomato (Solanum lycopersicum Mill.) fruit or Arabidopsis thaliana leaf. In this study, the extent of endoreduplication, epidermal cell area and number, were measured on successive compound leaves of a common tomato genotype (WVA 106). Neither the cell area, nor the endoreduplication factor differed significantly from one leaflet to another within a leaf at a given node. In addition, these two variables did not differ spatially in a mature leaflet, from tip to base. In contrast, both variables decreased from one leaf to another, i.e. from the most mature to the youngest without correlation with final leaf size. Results are discussed in terms of the respective role of endoreduplication and cell division in individual tomato leaf expansion. They give new insights into compound leaf formation at the cellular scale.
