Vol. 81 No: 5

Title:
Synthetic cytokinins extend the phase of division of parenchyma cells in developing pear (Pyrus communis L.) fruits

Authors:
A. SHARGAL, S. GOLOBOVICH, Z. YABLOVICH, L.A. SHLIZERMAN, R.A. STERN, G. GRAFI, S. LEV-YADUN and M.A. FLAISHMAN

pp: 915-920

Abstract:
Final fruit size in pear depends on the combined contributions of the number of cells present at fruit-set, the number of subsequent cell divisions, and on cell expansion. To date, in spite of the commercial application of cytokinins to induce larger fruits, no detailed studies have addressed the question of how cytokinin signalling and cell division regulate fruit growth under field conditions. As previously reported, ´Spadona` pear fruits treated once with N(2- chloro-4-pyridyl)-N`-phenylurea (CPPU) or N-phenyl-N`-1,2,3-thiadiazol-5-ylurea (TDZ) showed a significant increase in size compared to untreated fruit. Here we monitored the effect of CPPU and TDZ treatments on the number and size of parenchyma cells and stone cells in fruit pulp. Application of both synthetic cytokinins on 10 mmsized fruitlets had no effect on the size or number of stone cells during fruit development. However, the parenchyma that forms the fruit flesh, between the epidermis and the seed layers, had significantly smaller cells and produced higher numbers of cells compared to untreated fruit. The increase in parenchyma cell numbers correlated with a prolonged phase of cell division, as demonstrated by the detection of G2 nuclei using fluorescence-activated cell sorter (FACS) analysis. Hence a single spray with CPPU or TDZ can induce an increase in the diameter of pear fruit by extending the phase of cell division in parenchymal cells in the pulp.

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