Effects of heterochromatic knobs in maize sister inbred lines

Abstract

Maize heterochromatic knobs are chromosomal structures composed of highly repetitive DNA repeat arrays. They are variable among races, according to their geographical localization. They were mapped on meiotic and mitotic chromosomes by conventional and molecular cytogenetic methods. Tropical inbred lines, homozygous for different knob compositions were selected by the analysis of C-banded mitotic metaphases, and used to investigate knob effects. A group of these lines showed highly embriogenic response in tissue culture. Low frequency of mitotic instability was observed in the cultures and breaks occurred in chromosome possessing large knobs. Fertile plants regenerated from short-term cultures had normal chromosomes. Accumulation of alterations in knob-bearing chromosomes were detected in long-term-cultures. Correlations between genome size, knob content and flowering time has been reported. These relationships were not found in inbred lines and respective hybrids differing in the presence of four knobs. However, early flowering time was detected in lines and hybrids possessing the knob K9S.