Mutations Induced in Pea by X-Irradiation of Pollen and the Significance of Induced Unstable Chromosomes in Mutagenic Experiments

Abstract

SUMMARYIn the pea variety Parvus, emasculated flowers were pollinated with either X-irradiated or unirradiated ripe pollen. On 277 M1 plants coming from 750 R irradiation, 9 M1 plants segregated in M2 for mutations: all their sectors analyzed (main stems and branches) were interested by the mutations. Cytological analysis of M3 mutant types (variegated and chlorina-maculata leaf) has revealed the presence of unstable chromosomes such as dicentrics (in two mutations) and rings (in three mutations); the mosaic leaf phenotypes is due to breakage-fusion-bridge cycles included in the transmission of such chromosomes. Trisomic (2 n=15) plants beside normal and mosaic leaf phenotypes, have been originated in the M 3 segregation of the variegated and chlorina-maculata M2 mutants.The experiment pointed out that pollen treatment did not induce sectorial chimera in the M1 pea plants, so that a high segregation ratio of the induced mutations was obtained; this held true also when persistant chromosomal abnormalities involving breakage-fusion-bridge cycles, as dicentrics and rings, have been induced with a subsequent mixochimeric structure in the M1 plants.