Differential effects of specific chromosomal deficiencies on the development of the maize pollen grain

Abstract

A study was made of the differential effects of specific chromosomal deficiencies on the development of the maize pollen grain. Twenty-six B–A translocations involving 17 of the 20 chromosome arms were used to produce hypoploid plants in which one half of the microspores had a predictable chromosomal deletion. Breakpoints of the translocations were proximally located in most cases, although some were more distal. Deficient and normal male gametophytes from these hypoploids were studied cytologically to characterize developmental changes. Generally, loss of part of a chromosome arm caused abnormal microspore development, a slowing of the normal mitotic or developmental processes in the male gametophyte, or a termination of development. Slowing of development was observed as early as the quartet stage in deficient microspores from TB-1Sb and TB-9Sd hypoploids, while in others the developmental delay occurred later, mostly during the first pollen mitosis. The abnormal or blocked development associated with other deficiencies began as early as the quartet stage in deficient microspores of TB-1La hypoploids and as late as the first mitotic telophase in those of TB-6Lb, TB-6Lc, TB-9La, and TB-9Lc. The developmental modifications induced by the diverse deficiencies are dependent on the particular segment lost, demonstrating that components of normal microspore development identified in this study are controlled by genes located in specific parts of the genome.Key words: pollen, gametophyte, deletion, B–A translocations.