孑遗植物伯乐树的花粉和柱头特征研究

Characterization of Pollen and Stigma of Bretschneidera sinensis Hemsl.,a Tertiary Relict Tree

伯乐树是单种科植物和第三纪孑遗植物,零星分布于中国华南地区和越南北部,由于种群规模锐减被列为国家一级保护植物。本试验从传粉生物学角度研究其花粉的类型、活力变化、贮藏方法及柱头可授性,结果表明伯乐树雌蕊先熟,柱头在初开期迅速伸长,能有效避免自花传粉;柱头从小蕾期到盛开期间可授性逐渐增强,盛花期间的柱头表面具有粘液。花粉系非淀粉型,具典型虫媒特征;花粉粒初期在小蕾期活力极低,直至盛花期才具有较强的活力,体外萌发的适宜蔗糖浓度为20%。其花粉粒外壁较薄,对外界变化敏感,低温是保存其活力的必要条件,-20℃贮藏下的花粉活力可延长190 h。由于同一种群的花期较集中,对灾害天气的抗风险能力较弱,建议在盛花期搜集贮藏花粉以进行人工辅助授粉。

Bretschneidera sinensis Hemsl.,a monotypic species and Tertiary relict tree,is listed in the State First-Class Protection Tree Species of China. The natural population is decreasing nowadays with a sparse distribution ranged from south China to northern Vietnam. Within this study,we investigated the flowering behavior,pollen type,dynamic viability and storage method of pollen and receptivity of stigma. The elongation of the stigma at initial flowering stage was observed,which leads to the physical barrier compromising the self-pollination effectively. The receptivity of stigma developed form little bud to full-bloom stage,and mucilage was secreted by stigma only at full-bloom stage. Pollen grains were starchless which indicate a typical insect pollination. The viability of pollen was very low at bud stage,and then reached high at full-bloom stage. The optimal concentration of sucrose solution for in vitro germination was 20%. Pollen grains were observed to be sensitive responding to storage treatments. Pollen viability could be maintained up to 190 h under freeze storage(-20 ℃),suggesting that low temperature is the key factor to reserve the pollen viability. The resistance of the wild population upon climate change was quite fragile because the time-frame on the flowering of natural populations of B. sinensis Hemsl. was short. Thus,collection and low-temperature storage of mature pollen in combination with artificial pollination are recommended in B. sinensis Hemsl.