Chromosome pairing and its relationship to fertility in cytotypes of prairie cordgrass (Spartina pectinata Link)

polyploidy;fertility

Bishop, Jeffrey Wilson ; Rayburn ; Lane A

关键词: polyploidy;    fertility;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/88316/BISHOP-THESIS-2015.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Prairie cordgrass (Spartina pectinata Link) is a polyploid, perennial, C4 grass that isnative to North America. The species is able to produce large amounts of biomass, and it istolerant to a number of environmental stresses. Due to these characteristics, it is useful forpurposes such as bioenergy production, wetland restoration, soil erosion control, and forage. Thespecies is composed of three ploidy levels: tetraploids (2n=4x=40), hexaploids (2n=6x=60), andoctoploids (2n=8x=80). It is hypothesized that the hexaploid cytotype originated from thetetraploid cytotype, and therefore select populations of the two cytotypes are adapted to the samearea of the United States. This has provided the opportunity to study the effects of polyploidy onprairie cordgrass characteristics. Comparison of morphological traits between the two cytotypeshas shown that the hexaploid may be more desirable for commercial production than thetetraploid cytotype. However, prairie cordgrass has a low seed set, which is problematic forcommercial establishment and genetic improvement of the species. Polyploidy is known to affectfertility in other species, and therefore it may be the cause of reduced fertility in prairie cordgrassas well. In this study, chromosome pairing during meiosis I of microsporogenesis was analyzedin tetraploid, hexaploid, and octoploid prairie cordgrass cytotypes. Normal chromosome pairingand segregation was observed in tetraploids and octoploids whereas abnormality was observed inhexaploids. Chromosome pairing during meiosis I implied genome compositions of tetraploids,hexaploids, and octoploids were AABB, AAABBB, and AABBA’A’B’B’, respectively.Abnormality during meiosis I in the hexaploids may lead to inconsistent chromosome numbersin pollen grains, whereas normal meiosis I in the tetraploids is hypothesized to generate pollenwith consistent chromosome numbers. To investigate this potential effect, pollen morphologyand DNA content of pollen nuclei were analyzed in tetraploids and hexaploids. Analysis ofiiipollen morphology showed that micropollen was not formed as a result of abnormal meiosis I,suggesting that abnormal meiosis I may not lead to vast differences in chromosome in pollengrains. Flow cytometric analysis of pollen nuclei DNA content revealed that the distribution ofDNA content was significantly greater in hexaploids than in tetraploids, indicating that there maybe a slight degree of heterogeneity in chromosome number between pollen nuclei. However, thedegree of heterogeneity was lower than hypothesized. Seed set and seed germination wasevaluated in hexaploids and tetraploids to study the effects of abnormal meiosis I and potentialpollen heterogeneity. Seed set was slightly reduced in the hexaploids. A significant reduction inseed germination was observed in the hexaploids, though the magnitude of reduction was lessthan hypothesized. The results suggest that abnormal meiosis I in the hexaploid cytotype may notaffect seed set to a great extent. Furthermore, improvement of seed set may be attained throughselection, and the genome compositions of all prairie cordgrass cytotypes implied in this studymay be useful to the selection process.