In plant cells, differentiation begins with the very first cell division after the formation of the zygote; where elongation in the root stops; after the roots and stem have developed

The correct answer is - where elongation in the root stops.

Explanation:

Differentiation in plants is referred to as the arise of the cell from precursor cells. The differentiation gives rise to the new cells that are different to other cells that arise from the cell already exist. Differentiation in plants are takes place in the meristemic cells.

The differentiation in the plants begins just after the elongation in the root stop and meristemic cells start differentiating into a different types of cells to give rise plant.

Thus, the correct answer is - where elongation in the root stops.