A STUDY OF MEIOSIS IN THE PROGENY OF X-IRRADIATED LUZULA PURPUREA
In Luzula the chromosomes have diffuse or nonlocalized centromeres; thus, if the chromosomes are broken or rearranged by x-ray treatment, the changed chromosome patterns may survive through the mitotic cell divisions, on account of the centromeric action along the whole chromosomes. Hence, such plants with diffuse centromeres are able to survive and reach adult stages in spite of the fact that their chromosomes have been rearranged or broken by x-ray treatment of the seedlings. A study was made of plants selected from the progeny of material treated as seedlings with 1000 or 2500 r. Plants treated with stronger doses (5000 to 10000 r) were almost or completely sterile. The chromosome patterns of the root tips of X/sub 2/ plants were investigated in order to find plants with desirable chrom-osome patterns for the meiotic investigation. The x-irradiated plants themselves showed intricate metaphasic configurations during meiosis. The separation of the multi-associations at first anaphase is cytologically equational, and in most cases without bridges. Migration of chromatids during second anaphase is also regular without lagging chromosomes, but chromosome sets of 4 tetrad cells usually become unbalanced, causing reduced fertility. The mitotic chromosome patterns of X/sub 2/ plants showed three categories of patterns: 2n = 6; most of these plants have all chromosomes the same size, but some of them possess one long and one short chromosome indicating a reciprocal translocation between two chromosomes; 2n = 7, with one of the original chromosomes fragmented into two pieces; and 2n = 8, with two of the original chromosomes fragmented into two pieces each. A study was made of meiosis in X/ sub 2/ plants with a cytologically observable rearrangement in the root tips, determined as a reciprocal progeny plants were obtained. Meiosis of X/sub 2/ plants heterozygous for one chromosome fragmented into two pieces, i.e., possessing 2n = 7 with five normal-sized and two small half-sized chromosomes, was also studied. The expected course of meiosis was realized, giving rise to four balanced chromosome sets of the tetrads, two of them containing three normal- sized chromosomes and the remaining two having two normal-sized and two half- sized ones. These studied plants were all fertile. Examination of somatic chromosome patterns of the progenies originating from the X/sub 2/ plants heterozygous for one fragmented chromosome revealed the three expected chromosome patterns, i.e., 2n =6, 2n =7, 2n =8. X/sub 2/ plants with 2n =8 were homozygous for the fragmented chromosome, and had a completely regular meiosis with two large and two small bivalents during first metaphase and a regular pairing and separation during the second division. Consequently they gave rise to a fertile strain with a constart chromosome pattern. The origin of the aneuploidy and endonuclear polyploidy of material with diffuse centromeres was discussed in relation to the survival of the fragmented chromosomes in L. purpurea. The survival of broken chromosomes through consecutive generations thus gives an explanation of the occurrence of aneuploid chromosome numbers in material with diffuse centromeres. However, no interpretation of the phenomenon causing the survival of the fragments was provided by this study, since sufficient knowledge about the nature of the diffuse or nonlocalized centromeres is unavailable. (BBB)
- Research Organization:
- Agricultural Coll., Uppsala
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-18-000076
- OSTI ID:
- 4172169
- Journal Information:
- Hereditas (Sweden), Vol. Vol: 49; Other Information: Orig. Receipt Date: 31-DEC-64
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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