Parenchyma cell growth in potato tubers II. Cell divisions vs. cell enlargement

Abstract

Initial swelling and early tuber enlargement are the result of cell enlargement at a rate surpassing addition of new storage cells. New phloem strands are added by procambial activity. New storage cells are formed marginal to the phloem strands. Frequency of divisions in these new cells rapidly decreases. Tubers in which mitotic processes are compapratively restricted in early stages of development are slow growers; i.e., cell enlargement proceeds with fewer cells present. Tubers in which more phloem strands and associated cells have been added in early growth are rapid growers and contain more enlarging cells. Reduction in mitotic rate concurrently with increased cell enlargement progresses radially from each phloem strand in young tubers. Cell divisions are rare in all young storage tissues by the time a tuber has attained a size of 30 to 40 g, except in the immediate sites of “eye” buds. Some cell divisions are nececssary for phloem strands to keep pace with tuber enlargement, and also for formation of phellogen. Volumetric increase in these highly localized areas accounts for a small percentage of the increase in tuber volume resulting from enlargement of cells.