小麦颖果发育过程中韧皮部细胞的结构变化观察

利用光学显微镜、透射电镜和扫描电镜技术．对小麦颖果发育过程中韧皮部细胞的结构变化进行了系统观察。结果表明，开花后7d颖果还没有形成完全分化的维管束。开花后12d韧皮部可见明显的筛分子。每个维管束有大约40个左右的筛分子，它们呈半圆形分布于维管束外侧。开花后14～20d，筛分子内有较丰富的线粒体、P^-型质体和许多无定型丝状物，有些筛分子有珠光壁。筛分子有典型的伴胞，并形成SE／CC复合物结构。伴胞有稠密的胞质和核质。韧皮薄壁细胞与中间细胞间有丰富的胞间连丝；韧皮薄壁细胞间的胞间连丝呈区域集中分布。开花后24-29d，筛分子内线粒体数目减少，伴胞和韧皮薄壁细胞电子染色变浅，说明它们的养分运输能力下降。中间细胞的细胞质内仍有丰富的线粒体和其它细胞器，它们沿胞壁周缘分布；此时，中间细胞形成类似筛分子的结构．因此中间细胞是一种适应于养分运输的特化伴胞，在颖果灌浆后期起重要作用。开花后39d，韧皮部细胞衰老变形，此时颖果发育成熟。

Observation on the structure change of phloem cells in the developing wheat caryopsis

The structure change of phloem cells in developing wheat( Tritium aestivum. L ) caryopsis was systematically investigated via optical microscopy, scan electron microscopy and transmission electron microscopy. The results showed that the main vascular bundle did not appear to be fully differentiated at the 7 th day after anthesis. The fully differentiated sieve elements could be observed at the 12 th day after anthesis. The estimated number of sieve elements was about forty and they distributed as semi circular at the outside of vascular bundle. From 14 th to 20 th after anthesis, the SEs were enriched with mitochondria, P type plastid, and many microfibril like structures. Some SEs had Nacreous Wall. Some SEs had typical CC and SE/CC complex could be formed. CCs contained electron dense protoplasm and nucleus. Numerous plasmodesmata were found between intermediary cell and phloem parenchyma cell; or between phloem parenchyma cells. There were plasmodesmata zones existed between phloem parenchyma cells. From 24 th to 29 th day after anthesis, the number of mitochondria decreased in SEs, CCs and phloem parenchyma cells contained electron light protoplasm, these means that their transport function were decreased. Intermediary cells still contained numerous mitochondria and other cell organelles. Intermediary cells had same structure as SE when the protoplasm of intermediary cell was pushed to all around of cell cavity. So intermediary cells were some special parenchyma cells that suited to photoassimilate transport. It had an importance function during later filling stage. The 39 th after anthesis, phloem cells became feeble and deformed; wheat caryopsis developed mature.