Nuclear DNA changes within Helianthus annuus L.: origin and control mechanism

Area of Science:

• Plant genetics
• Molecular biology
• Cytology

Background:

• Previous studies indicated nuclear DNA content variability within Helianthus annuus progeny.
• This variation was linked to the seed's position on the flower head.

Purpose of the Study:

• Investigate DNA changes during development in Helianthus annuus.
• Identify the mechanism controlling DNA variation in seeds based on head portion.

Main Methods:

• Utilized cytophotometric determinations with Feulgen-staining.
• Analyzed DNA content in mitotic prophases, meiotic prophases I, and early heart-shaped embryos.
• Examined DNA content in seedlings from seeds developed in different head locations.

Main Results:

• Consistent Feulgen absorption values were observed in mitotic and meiotic prophases across all flower parts.
• Significant differences in Feulgen/DNA content were found in early embryo prophases, increasing from the head's center to periphery.
• Observed DNA variations were not due to chromosome number changes but involved heterochromatic regions.
• Seedling DNA content reflected maternal plant levels and seed location, with progeny variation spanning the line's full range.

Conclusions:

• Nuclear DNA content variation in Helianthus annuus originates during early embryogenesis, specifically in heart-shaped embryos.
• The observed DNA changes are linked to heterochromatic regions and are influenced by seed position within the flower head.
• This positional effect impacts subsequent seedling development and contributes to the overall genetic variability within the progeny.