Chromosome constitution and cell division in in vitro cultures ofZea mays L. endosperm

Summary Cultures of maize (Zea mays L.) endosperm grown in vitro for over 3 years were examined cytologically. Conditions of aneuploidy and polyploidy were noted. Chromosome numbers ranged from 21 to over 200, with 30 to 60 being observed most often. Although a few extra large cells with polyploid nuclei were scattered throughout the smear preparation, a large proportion of the interphase nuclei appeared similar in volume and probably contained a near normal complement of chromosomes. Anaphase bridges were the most commonly observed chromosome aberration. No cell divisions were observed the first 24 hr after transfer. From 2 to 8 days after transfer the proportion of cells in division was relatively constant with a mitotic index of approximately 5.5%. The proportion of cells in division began to decline 8 days after transfer and in the final sample taken after 13 days only 2.6% of the cells were in division. Examples of localized synchrony were observed and mitotic indices for individual cell clumps ranged from 0 to 17%. Authorized for publication on October 16, 1973 as paper number 4552 in the Journal Series of the Pennsylvania State Agricultural Experiment Station.