CPD banding patterns and identification of 45S rDNA sites in tomato.

In this study, we performed sequentially combined PI and DAPI (CPD) staining and FISH with two different 45S rDNA clones on meiotic pachytene and mitotic metaphase chromosomes in tomato. Ten red CPD bands were shown on eight pachytene bivalents, and 12 bands were shown on six pairs of mitotic metaphase chromosomes. The CPD bands exhibited on mitotic metaphase chromosomes corresponded to the prominent bands exhibited on the pachytene chromosomes. The distinctive CPD bands, which could be constantly and clearly detected using the CPD staining procedure we improved, provided new landmarks for chromosome identification in tomato. FISH with the tomato 45S rDNA clone revealed very strong signal(s) in the satellite(s) on the short arm of chromosome 2 as well as weak signals in five CPD banded regions at pachytene or four pairs of CPD banded regions at metaphase chromosomes. However, FISH with pTa71 plasmid only revealed signals in the satellite. Considering the difference in sequence between the two rDNA clones, we inferred that only the satellite contains the coding regions of 45S rDNA unit in tomato. The property of CPD bands as well as the DNA sequences probably involved in the five CPD banded regions was discussed.