CELL NUMBER, CELL-SIZE AND HORMONE LEVELS IN SEMI-ISOGENIC MUTANTS OF LYCOPERSICON-PIMPINELLIFOLIUM DIFFERING IN FRUIT SIZE

Tomato fruit growth parameters, cell number and cell size, and hormone levels [IAA, abscisic acid (ABA), zeatin (Z)/zeatin riboside (ZR), isopentenyladenosine (i-Ado)/isopentenyladenine (i-Ade)], in the wild-type (Lycopersicon pimpinellifolium Mill.) and a semi-isogenic mutant (mutant III) differing in fruit size were investigated during fruit development. An image-processing system was used for the determination of cell number and single cell size per fruit and hormone levels were measured by radioimmuno-assay (RIA). The bigger fruits of mutant III showed higher cell numbers throughout fruit development and cells enlarged faster than in wild-type fruits. During the first 10 days of fruit growth, the main cell division period after fertilization, high concentrations of cytokinins were found, these being correlated with high cell division activity. There were only slight differences in IAA and ABA levels in the different sized fruits. The results emphasized the importance of the cell number per fruit at anthesis as a determining factor of final fruit size in tomatoes. A possible relationship between cytokinins and subsequent fruit development is discussed.