Abstract:

Objective: The purpose of this study is to establish the corresponding relationship between morphological indicators of flower development and the meiotic process of Hydrangea, and to observe the chromosome behaviors in microspore mother cells and the pollen characteristics, so as to lay the foundation for the germplasm innovation of Hydrangea. Method: The inflorescences at different developmental stages were collected and pressed onto a glass slide and stained with carbol fuchsin, and the meiotic process of pollen mother cells (PMCs) of fertile flowers was observed. The proportion of abnormal meiotic phenomena was counted, and the pollen was cultured a liquid pollen germination medium and the pollen germination rate was measured. Result: 1) Before the opening of decorative flowers around the inflorescence of Hydrangea macrophylla ‘Endless Summer’, the PMCs of fertile flowers displayed condensed cytoplasm and prominent nucleoli. When the decorative flowers at the edge of the inflorescence opened slightly, the fertile flower buds were 3–3.5 mm in diameter, and their anthers were about 0.5 mm in width and 1 mm in length. At this point, the PMCs meiosis entered the pachytene stage. With further development of fertile flowers, various stages from diakinesis to pollen grains were able to be observed. When the decorative flowers at the edge of the inflorescence were fully open the meiosis process terminated. At this time, the buds of fertile flowers were about 4 mm in diameter, and the anthers were about 1 mm in width and 1.5 mm in length. 2) The chromosome of H. macrophylla ‘Endless Summer’ PMCs behaved normally during meiotic process. The meiotic process of the microspore mother cells of the two hybrids F₁ showed a lot of abnormal phenomena. In the hybrid of H. macrophylla ‘Magical Jade’ × H. chinensis, 46.41% of the microspore mother cells showed chromosomes detached from the equatorial plate at meiosis metaphase I stage, 52.48% of the cells had laggard chromosomes or formed chromosome-bridge at anaphase I and telophase I stage. Micronucleus appeared in 35.11% of the cells at the telophase II stage. In the H. macrophylla ‘Taube’ × H. macrophylla ‘Veitchii’ hybrid, the rate of unpaired chromosomes in metaphase I was 15.31%, and around 17.30% of cells showed laggard chromosomes or chromosome-bridge at anaphase I and telophase I stage. No micronucleus was observed in the telophase II period. 3) The pollen grains of H. macrophylla ‘Endless summer’ were spherical and uniform in size, with a diameter (16.72±0.75) μm and pollen germination rate was about (25.15±3.54)%. The diameter of the pollen grains of H. macrophylla ‘Taube’× H. macrophylla ‘Veitchii’ hybrid F₁ was (16.60±1.73) μm, and the pollen germination rate was about (16.26±1.72)%. The spherical pollen grains of H. macrophylla ‘Magical Jade’ × H. chinensis hybrid were able to be divided into two categories: the diameter of small pollen grains was (16.48±0.71) μm, and that of large pollen grains was (23.30±1.82) μm, which was about 1.41 times larger than the small pollen grains. The large pollen is speculated to be 2n pollen, which accounted for (6.12±1.01)% of the total pollen grains. Conclusion: The decorative flowers on the edge of the inflorescence are slightly open, and the diameter of the fertile flowers buds is 3–4 mm, which can be used as a marker of the initiation of meiosis of pollen mother cell in the Sect. Petalanthae of Hydrangea. H. macrophylla ‘Endless Summer’ and the hybrid of H. macrophylla ‘Taube’ × H. macrophylla ‘Veitchii’ have high pollen germination rate and can be further used as hybrid parents in later breeding work.

Key words: Hydrangea, pollen mother cells, meiosis characteristics