Heterogeneity of heterochromatin in plants: Comparison of Hy- and C-bands inVicia faba

The comparison of Hy- and C-bands reveals three types of heterochromatin (Hy+, Hy−, and Hy 0) inVicia faba. By C-banding, the total of constitutive heterochromatin is identified. The Hy-banded heterochromatin is restricted to the M-chromosome: The nucleolus-associated heterochromatin appears as two darkly stained (Hy+)-bands bordering the secondary constriction, while reduced staining (Hy−)-bands are located near the centromere. The heterochromatin of the S-chromosomes is of the (Hy 0)-type, i.e., it does not respond to the Hy-banding procedure. A complete karyogram of the C-banded chromosome complement is presented and discussed. A comparison of C-bands and cold-sensitive segments clearly shows that negatively as well as positively reacting cold-induced segments are partly heterochromatic, partly euchromatic.