INTERFEROMETRIC CHANGES IN ONION NUCLEI AND NUCLEOLI DURING DEVELOPMENT

Abstract

SUMMARYThe inner epidermis of the outermost (1) through to the innermost (7) bulb scales of mature white onions were studied by means of quantitative interferometry. Scale 7 represented the oldest unemerged leaf, whereas scales 1 to 6 represented mature leaf bases whose blades had grown, emerged, and withered. A developmental sequence was observed from scale 7 through to scale 1. Nuclei increased in area from 2.9 × 10−6 cm2 in scale 7 to 9.9 × 10−6 cm2 in scale 1, with the greatest increases among the younger scales. Nucleoli increased in area from 3.7 × 10−8 cm2 in scale 7 to 13.9 × 10−8 cm2 in scale 2. Dry mass per unit area of the nuclei increased from 7.8 × 10−5 g/cm2 in scale 7 to 12.4 × 10−5 g/cm2 in scale 1, with a maximum of 13.7 × 10−5 g/cm2 in scale 3. Nucleoli increased in dry mass per unit area from 6.2 × 10−5 g/cm2 in scale 7 to 9.2 × 10−5 g/cm2 in scale 1, with a maximum of 11.6 × 10−5 g/cm2 in scale 3. Nuclear dry mass increased from 2.1 × 10−10 g in scale 7 to 12.1 × 10−10 g in scale 1. Nucleolar dry mass increased from 2.3 × 10−12 g in scale 7 to 12.9 × 10−12 g in scale 1. The data suggest that nuclei and nucleoli increase in size and mass with cell size, thereby providing a greater biosynthetic (control) capacity to enlarging cells.