Cytological mechanism of 2n pollen formation in Chinese jujube (Ziziphus jujuba Mill. ‘Linglingzao’)
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In order to elucidate the cytological mechanism of 2n pollen formation in Chinese jujube, a cultivar named ‘Linglingzao’ (2n = 2x = 24) which produces relative more 2n pollens naturally was employed for microsporogenesis analysis. Chromosomes paired in 12 bivalents at diakinesis and the first meiotic division was normal, whereas, the second division was characterized by frequent abnormal spindle orientation (parallel and tripolar spindles). Perpendicular, tripolar, and parallel spindles at metaphase II accounted for 72.93, 17.22, and 9.85% respectively. Perpendicular and tripolar spindles led to tetrads and triads formation respectively. Two types of parallel spindles were observed and a significant association correlation (r = 0.84, P < 0.05) between parallel spindle II (fused spindles) and dyads was found which meant only fused spindles can form dyads, while parallel spindle I with a long distance between two sets of chromosomes seemed to lead tetrad formation. At tetrad stage, the observed frequencies of tetrads, triads and dyads were 80.99, 16.40, and 2.61% respectively. By the rule that each tetrad can form four n pollens, each triad can form one 2n pollen and two n pollens, each dyad can form two 2n pollens, the frequency of 2n pollen estimated was 5.71%. Based on the pollen diameter difference between n and 2n pollens, frequency of 2n pollen observed was 6.15%. No significant difference was observed between frequency of 2n pollen estimated and that of observed. The results indicated that, tripolar spindles and fused spindles at metaphase II followed by more triads and few dyads formation at tetrad stage were responsible for the production of 2n pollen in Chinese jujube. 2n gametes observed correspond to first division restitution. Research on the cytological mechanism of unreduced pollen will provide a platform for unreduced pollen induction and polyploidy breeding in Chinese jujube.
KeywordsMeiosis Triads Dyads 2n gametes Polyploidization
The authors want to thank the National Key Technology R&D Program (2007BAD36B07, 2008BAD92B03), the Provincial Natural Science Fund of Hebei (C2007000452) and Agricultural Scientific Research Achievement Transformation Program (2010GB2A200027) for financial assistance.
- Camadro EL, Saffarano SK, Espinillo JC, Castro M, Simon PW (2008) Cytological mechanisms of 2n pollen formation in the wild potato Solanum okadae and pollen–pistil relations with the cultivated potato, Solanum tuberosum. Genet Resour Crop Evol 55:471–477. doi: 10.1007/s10722-007-9254-1 CrossRefGoogle Scholar
- Geraci G, Esen A, Soost RK (1975) Triploid progenies from 2x × 2x cross of Citrus cultivars. J Hered 66:177–178Google Scholar
- Hancock JF (1997) The colchicine story. HortScience 32:1011–1012Google Scholar
- Hayashi M, Kato J, Ohashi H, Mii M (2009) Unreduced 3x gamete formation of allotriploid hybrid derived from the cross of Primula denticulata (4x) × P. rosea (2x) as a causal factor for producing pentaploid hybrids in the backcross with pollen of tetraploid P. denticulata. Euphytica 169:123–131. doi: 10.1007/s10681-009-9955-y CrossRefGoogle Scholar
- Peng B (2008) Study on 2n pollen in Chinese jujube. Dissertation, Agricultural University of HebeiGoogle Scholar
- Sugiura A, Ohkuma T, Choi YA, Tao R, Tamura M (2000) Production of nonaploid (2n = 9x) Japanese persimmons (Diospyros kaki) by pollination with unreduced (2n = 6x) pollen and embryo rescue culture. J Am Soc Hortic Sci 125(5):609–614Google Scholar
- Van Tuyl JM, Lim KB (2003) Interspecific hybridisation and polyploidisation as tools in ornamental plant breeding. Acta Hortic 612:13–22Google Scholar
- Veilleux R (1985) Diploid and polyploid gametes in crop plants: mechanisms of formation and utilization in plant breeding. Plant Breed Rev 3:253–288Google Scholar
- Xu LQ, Zhang QL, Luo ZR (2008) Occurrence and cytological mechanism of 2n pollen formation in Chinese Diospyros spp. (Ebenaceae) staminate germplasm. J Hortic Sci Biotech 83(5):668–672Google Scholar