INTERFEROMETRIC CHANGES IN ONION NUCLEI AND NUCLEOLI DURING DEVELOPMENT

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Abstract
SUMMARY: The 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.