蚕豆种皮内维管束分布及卸出部位结构

VASCULAR BUNDLE DISTRIBUTION WITHIN BROAD BEAN SEEB COAT AND THE STRUCTURE OF UNLOADING REGION

蚕豆(Vicia faba)种子通过珠柄与果皮脊部的大维管束相连。维管束经种脐,以及穿越种脐和外种皮的两层栅栏组织进入种皮的薄壁组织后分成两路:一路是完整维管束经种皮背部向下穿行,经底部到胚根处终结;另一路是只有韧皮部而无木质部的两条反向维管束,向前延伸经珠孔空腔两旁向下稍延伸,它们并不与由下而上的另一条完整维管束沟通。反向维管束有较多的小分叉。反向维管束的韧皮部与完整维管束的明显不同之处在于前者的伴胞通常不转化为传递细胞,而与相邻的薄壁细胞间却有大量胞间连丝。由结构分析推测,输入种皮的同化物的种皮卸出与向胚胎转运的过程中,尤其在反向维管束区域内,共质体途径占有重要地位。

Cytological observations were made on developing seed coat of broad bean (Vicia faba L.) by use of light and electron microscopy. Attention was focused on vascular distribution. The seeds were attached by the funiculus to the large vascular bundles of pericarp of broad bean. The vascular bundle passed through hilum and two layers of palisade, entered the pa- renchyma of seed coat, then diverged in to two routes. One was a complete vascular bundle com- posed of both phloem and xylem elements, ir stretched down through seed raphe, then upward and terminated near the radical. The other was a two-recurrent-vascular-bundle with only phloem constitutents, they extended forward detoured the micropyle and extended downward. but did not join with the upward complete vascular bundle. The recurrent vascular bundles branched out many small short branches. The obvious difference between phloem of recur- rent vascular bundle and of complete vascular bundle was that the companion cells of the for- mer did not normally modify to transfer cells, but connected to the adjoining parenchyma cells through abundant plasmodesmata It is deduced from the structural analysis that the symplas- tic route may play an important role, particularly in the region of recurrent vascular bundle, in the course of importing assimilates unloading in seed coat and transporting to the embryo.