无籽西瓜胚轴维管束转位的观察

借助石蜡切片技术对无籽西瓜胚轴进行连续切片和系统镜检。在根茎过渡区连续横切面上,可看到由根部四原型外始式初生木质部与初生韧皮部相间排列的维管束转变到茎部成为四原型、内始式和双韧并生排列的维管束。转化经过分叉、倒转和合并,是不同步的,从左到右沿顺时针力向逐步转变。中胚轴子叶迹发生处延伸出2个小束。根、茎维管束转换区发生在下胚轴。该区外形较粗大,生理活性较强,对外界条件变化较敏感,是瓜苗抗性最弱部位,也是组培择取外植体最合适的节段。可为瓜苗耕作管理和择取外植体提供形态学参考指标。

AN OBSERVATION ON THE TRANSITION REGION OF VASCULAR BUNDLES IN THE HYPOCOTYL OF SEEDLESS WATERMELON

The hypocotyl of seedless watermelon was continually sectioned and systematically observed with the aid of paraffin section technique. Observations showed that the transformation from primary vascular bundle of the root radilly arranged in exarch tetrarch to bicollateral bundle of stem collaterally arranged in endarch tetrarch occurred in the cross section of transition region. The eight small bundles in the mesocotyl were gradually formed from right to left clockwise. Every pair of small bundles from different sources by the cotyledon trace drew close quickly and combined into four bicollateral bundles in collateral arrangement after changing the direction of differentiation position by 180 degrees. Another two small bundles were differentiated in the place where cotyledon trace of epicotyl took place. The transition region of vascular bundles of root and stem was at the hypocotyl where the contour was thicker than any other position. This part of the seedling performs more active physiological function and is more sensitive to environmental condition but weaker in resistance. It can be used as a morphological criterion for cultivation management.