Abstract:The ultrastructure and nucleus development of dedifferentiating cell in tissue culture of hypocotyl cotyledon leave in Astragalushuangeensis are observed and analysed,Mitochondria, golgi and polyribosomes increase in dedifferentiating cell,There is accumulating starch in plastid.A developmental process between nucleolus and heterochromatin is observed in dedifferentiating cell.This process is called as "nucleolus matter sprey" phenomenon temporaryly,It can be divided into a few stages:1.Nucleolusenglarges and heterchromatin condenses near the nuclear membrance. NOR.(nucleolar organizer regions)appear evidently a:spherical bodies in direct contact with the nucleolus.2.The heterchromatin move to the nucleolus and get in contact with the nucleolus. The nucleloar organizer regions disappear. Part of heterchromatin enter the nucleolus.3.The substance in nucleolus mix with heterchromatin entering into nucleolus,then the mixture is sprayed in form of band and pearl.The process occurs before the earlier mitosis prophase. It seems to be considered as mark of dedifferentiating cell.