Effects of nitrogen deprivation on cell division and expansion in leaves of Ricinus communis L.

The effects of nitrogen deprivation on leaf extension, cell numbers and epi dermal cell size were followed in leaves of Ricinus communis L. The extent to which reductions in final cell number or final epidermal cell size contr ibuted to the reduction in final leaf size depended on the developmental st age of the leaf at the time of N deprivation. In leaves which already had t heir full complement of cells (leaf 2), the reduction in final leaf size fo llowing nitrogen deprivation was associated with a reduction in final cell size. In leaves that were at earlier stages of development at the onset of N deprivation (leaves 3 and 4), the reduction in final leaf size was greate r than in leaf 2. In these younger leaves, the final cell size was even sma ller than in leaf 2, but the greatest contribution to reduced final leaf si ze was a reduction in the number of cells produced. This accounted for appr oximately 80% of the reduction in final leaf size in leaf 4. During leaf de velopment, the contribution from different tissue layers to the total cell number changed. In the smallest leaf sizes, the contribution from upper and lower epidermis and spongy parenchyma was greater than that from palisade parenchyma. As the leaf size increased, cells in the palisade parenchyma co ntinued to divide for longer than in the other layers. At final leaf size, the contribution from the different tissue layers to total cell number was the same for leaves 2, 3 and 4, irrespective of N treatment. In these final leaf structures, palisade parenchyma contributed 60% of the total cell num ber. Thus, although nitrogen deprivation affected leaf size variously throu gh cell division and cell expansion, depending on leaf developmental stage at the time of nitrogen deprivation, the ratio of cell numbers and sizes in different tissue layers, at final leaf size, was unaffected.