中国特有濒危植物伯乐树叶的结构特征

Leaf Structural Characteristics in Bretschneidera sinensis,a Rare Endemic Plant in China

伯乐树(Bretschneider asinensis Hemsl.)是中国特有濒危的第三纪孑遗植物。采用石蜡切片、刮片法和扫描电镜等技术研究了叶的结构和表皮微形态特征。结果表明,伯乐树表皮细胞的形状无规则,垂周壁稍弯曲,外壁角质膜较薄;上表皮细胞壁上被条纹状的蜡质;气孔仅见于下表皮,略下陷,其周围的表皮细胞向外呈鲜花状隆起;栅栏组织一层,海绵组织较发达,多层,内有含芥子酶的分泌细胞和含晶细胞。叶片厚度、栅栏与海绵组织厚度比值和叶绿体大小等随不同发育时期及部位有较明显变化,表明了在生长过程中苗期需要荫蔽生境,而成株则趋向中性生境的特殊要求;其下表皮细胞上鲜花状隆起结构仅与无患子目的无患子科相似,但与该科存在其它差异,为此,支持了伯乐树科在无患子目中与无患子科亲缘关系较近并独立成科的观点。

Bretschneidera sinensis is a rare endemic and tertiary relict plant of China.Its structural and epidermis micro-morphological characteristics were studied by paraffin section,scraping section and scanning electron microscopy （SEM）.Results showed that the epidermal cells were covered with a thin cuticle layer,the cell shape was irregular and the patterns of anticlinal walls were sinuolate.The upper epidermis was covered with barred wax and the sunken stomatas only presented on the lower epidermis,which was surrounded by flower-like neurite structures.Mesophyll tissue included one-layer of palisade tissue,accompanied with multi-layers of well-developed spongy tissue containing secreting cells with myrosinase and crystals cells.Significant changes in leaf thickness,ratio of spongy to palisade tissue thickness （S/P）,and volume of chloroplast were presented in the different phases and zones,indicating a special change from sciophytes to mesophytes during the growth process.The close relationship between Bretschneideraceae and Sapindaceae was supported from the flower-like neurite structures found in the abaxial epidermis （similar to Sapindaceae）,while differences showed the independence of Bretschneideraceae in Sapindales as a family.