Giemsa C‐banding and silver‐staining for cytological studies in Pisum

Technical hints are given for Giemsa C‐banding of the Pisum chromosomes and for silver‐staining of NORs and nucleoli. C‐band positive heterochromatin appears as pairs of centromeric dots on each of the seven chromosomes and as heavily stained C‐bands at the secondary constrictions in the long arms of chromosomes 4 and 7. In the latter arm, there is also an intercalary proximally situated C‐band. The centromeric dots are attached to chromosomal spindle fibres, which supports the supposition that they are kinetochores. The C‐blocks of the SAT regions are also detectable at metaphase I of meiosis and hence facilitate the interpretation of configurations in structural hybrids involving the SAT chromosomes. In mitotic interphase nuclei, the SAT blocks appear as four chromocentres, and in the giant nuclei of the suspensor, as four endochromocentres. Ag‐NORs coincide with the C‐bands at the SAT regions. Moreover, the centromeric dots are stained by silver nitrate. In Pisum , nucleoli may be formed from the centromeric regions of the chromosomes. At late mitotic prophase (diminishing stage of nucleolar development), the nucleoli sometimes appear as paired heavily silver‐stained bodies budding out from the chromosomes. At meiotic prophase, darkly stained intranucleolar bodies occur in slides prepared according to a suitable silver‐staining technique.