The relationship between genome size and synaptonemal complex length in higher plants.

There appears to be only a weak correlation between genome size and the corresponding total length of a complete set of synaptonemal complexes (SCs) based on published evidence for several fungal, plant, and animal species. This result is unexpected, considering the strong positive correlations between genome size (DNA amount) and total chromosome length and volume and between relative lengths of chromosomes and SCs. Because the observed weak correlation was based on limited data, we systematically investigated the relationship between genome size and SC length, using ten higher plant species. Two-dimensional spreads of SCs from primary microsporocytes at pachytene were prepared using a hypotonic bursting technique. The SC spreads were examined either by light or electron microscopy, and the lengths of at least ten complete sets of SCs were measured for each of the ten species. Additionally, the genome size of each species was determined from pollen tetrad protoplasts using flow cytometry. A strong correlation (r = 0.97) between total SC length and genome size was observed for higher plants, indicating a constant amount of DNA is associated with a given length of SC, at least when averaged over the whole genome.