DISTRIBUTION OF HETEROCHROMATIN IN THE CHROMOSOMES OF HAPLOPAPPUS GRACILIS

Abstract

Several approaches were employed to study the distribution of heterochromatin in root tip chromosomes of Haplopappus gracilis. Cold treatment and pretreatment in an aqueous solution of 8-hydroxyquinoline revealed achromatic gaps in metaphase chromosomes. Cold treatment also permitted the demonstration of positive heteropycnosis in prophase chromosomes. Further support for the identification of heterochromatic segments was provided by a study of the localization of chromosome aberrations induced by maleic hydrazide and an analysis of the pattern of DNA synthesis in chromosomes of root tip cells. Seven of the ten regions that were preferentially broken by maleic hydrazide also reacted differentially to cold treatment or to pretreatment with 8-hydroxyquinoline. A good correlation was found between regions that completed DNA replication late in the DNA-synnhetic period and segments that were shown to be heterochromatic by the other techniques.