A model for change in cpDNA and nuclear DNA (nDNA) amount during development. The change in parameters affecting cpDNA and nDNA amount between immature and mature tissues is represented. Two cell types are shown, along with the net change expected for a population of both cell types. Arrows indicate an increase or decrease. Dashes indicate no change. In Type 1 cells, cpDNA/plastid and plastids/cell are constant, and the nDNA increase leads to a decrease in cpDNA/nDNA. In Type 2 cells, cpDNA/plastid declines, but both plastid number and nDNA remain constant, leading to a decrease in cpDNA/nDNA. The net change for the population is an increase in nDNA, no change in plastids/cell, and a decrease in both cpDNA/plastid and cpDNA/nDNA. Shaded boxes indicate the parameters used to calculate plastomes/cell, based on qPCR and mean ploidy using flow cytometry. Data obtained from these methods represent the net change in nDNA and cpDNA/nDNA for the population and do not assess the cpDNA/plastid. The net increase in nDNA/cell is similar to the net decrease in cpDNA/nDNA because Type 1 cells contribute to the increase in ploidy without contributing greatly to the change in cpDNA/nDNA. As a result, calculation of plastomes/cell yields a similar value for immature and mature tissues, and there appears to be no net change in plastomes/cell (left half of the box in the bottom right corner). If qPCR and flow cytometry could be performed on each cell type separately, calculation of plastomes/cell would reveal no change for Type 1, a decrease for Type 2, and a net decrease for the population (right half of the box), because the contribution of individual cells to the increase in nuclear ploidy and decrease in cpDNA/nDNA could be assessed.