Cell Division and Enlargement in Mesocarp Parenchyma of Gibberellin-Induced Parthenocarpic Peaches

Gibberellin at concentrations of 50, 250, and 500 mg/l sprayed on branches bearing emasculated blossoms at the time of full bloom induced parthenocarpy in the Fay Elberta peach. 2. Eleven weeks after bloom no statistically significant difference occurred among the mean numbers of parenchyma cells along the mesocarp radii in pollinated fruits and in parthenocarpic ones induced by the different GA concentrations. This indicates that the GA concentration was not critical in stimulating cell division to the normal extent in unfertilized peach ovaries, at least within the range of concentrations used here. 3. Significant differences in mean cell volumes of mesocarp parenchyma occurred between parthenocarpic fruits induced with 50- and 250-mg/l concentrations and the mean cell size in pollinated fruits. The mean cell volume in fruits induced with the 500-mg/l concentration was not significantly different, however, from the mean in pollinated fruits. The degree of cell enlargement was thus related to the GA concentration applied. 4. The only microscopic differences found in the mesocarp of parthenocarpic as contrasted with pollinated fruits were evidences of increased cell-wall plasticity in fruits induced with 250- and 500-mg/l concentrations and the much larger amounts of starch stored in cells of fruits produced with 50 mg/l. 5. Thus one application of GA at a concentration of 500 mg/l almost exactly reproduced in the parthenocarpic fruits the effects, as concerns mesocarp growth and development, that follow fertilization in pollinated fruits.