Study On Cytogenetics In Autotetraploid Radish

Cytogenetics of autotetraploid Raphanus sativus L. was studied in this paper. Meioticbehaviours of pollen mother cells (PMCs), development of male gametophyte andkaryotype were observed on the bases of chromosome preparation. It served as a solidtheoretical fundamental and guide of polyploid breeding of radish.1. Meiosis of pollen mother cellsThe chromosome meiotic behaviors during pollen mother cell (PMC) development ofcolchicine-induced radish were carried out by a routing method. The results demonstratedthat: the PMCs meiosis of autotetraploid was similar to the diploid except someparticularities: about 19.3％PMCs had bi-nucleoluses and in metaphaseⅠ, 13.8％multivalent, 46.5％quadrivalent, 38.9％bivalent were observed. The chromosomes, not torank at metaphase plate in metaphaseⅠand metaphaseⅡcells accounted for 25.5％. Therewere also lagged chromosomes, chromosome bridge and fragment in anaphaseⅠandanaphaseⅡcells. Spindles during metaphaseⅡconsisted parallel style, vertical style andthe"八"like style. At tetrad stage, dyad, triad, tetrad with micronucleus appeared. Theemergence frequency of abnormal phenomena in each stage of meiosis was 32.0％intetraploid and 12.1％in diploid, which indicated that the genetic stability of autotetraploidradish was much lower than that of diploid which indicated that abnormal meiosis of PMCswas the cytogenetic reason of fertility reduction of autotetraploid radish pollen.2. Development of male gametophyteThe continuous development of male gametophyte in autotetraploid radish wasobserved by the way of Ehrlich's hematoxylin staining-methyl salicylate cleating technique.The results indicated that the male gametophyte in autotetraploid radish shared the similardevelopment with that in diploids, which could produce one vegetative cell and onegenerative cell by the first mitosis, and the generative cell could divide into two sperms by the second mitosis in succession. The mature pollen was 3-celled with two, three or fourapertures while the diploids basically three. Abnormality appeared mainly in tetrad anduninucleate stage of male gametophyte development with an average frequency of 32％,which was 20％higher than that in the diploids.3. Karyotype analysisIn the study of karyotype of radish, chromosome preparation flow was confirmed asfollows: the seeds were dipped in water at 4℃for 12 hours and cultered at constanttemperatue. And then select the strong seeds at the length of 0.5cm to 1.2cm to pretreat.And pretreatment with mixture of ice and water or 8-Hydroxyquinoline could reach thebest result, namely, chromosomes were fairly well-dispersed, the primary and secondaryconstrictions were distinct and the chromosomes with satellite were easy to be identified.And then fixed up in Camoy's for about 8 to 24 hours and macerated in 60℃1N HCl for10 minutes. The diploid karyotype was formulated as 2n=2x=18=10m+8sm, whichindicates a Stebbins's 3A type and the tetraploid formulated as 2n=4x=36=24m+12sm,which indicates a Stebbins's 2A type. The relative length of diploid ranged from 8.23％to13.61％, while tetraploid ranged from 7.86％to 13.86％.