Warmbrodt Robert D
Department of Botany, The Ohio State University, Columbus, Ohio 43210, USA.
New Phytol. 1986 Jan;102(1):175-192. doi: 10.1111/j.1469-8137.1986.tb00808.x.
The primary phloem and associated tissues in the root of Cucurbita pepo L. were examined by light and transmission electron microscopy to provide information on the feasibility of symplastic transport from the sieve-tube members to the cortex in this organ. The structure, distribution and frequency of cytoplasmic connections between the various cell types of the root are reported as well as the cytological characteristics of the various cells. The protoplasts of contiguous cells of the root are joined by various numbers of cytoplasmic connections: plasmodesmata (simple and branched) between parenchymatous elements; pore-plasmodesmata between sieve-tube members and parenchymatous elements (companion, phloem parenchyma or pericycle cells in the Cucurbita root); and sieve-area pores between contiguous sieve elements. The plasmodesmata associated with secondary- and tertiary-state endodermal cells are not constricted by the suberin lamellae. Differences in the frequency of cytoplasmic connections between the various cell types of the primary phloem, pericycle and ground tissue do occur with the highest frequency between sieve-tube members and companion cells. The results indicate that the structure of the C. pepo root may be compatible with a symplastic pathway of phloem unloading and transport to the cells of the ground tissue.
利用光学显微镜和透射电子显微镜对西葫芦根中的初生韧皮部及相关组织进行了研究，以获取关于该器官中从筛管分子到皮层的共质体运输可行性的信息。报告了根中各种细胞类型之间胞质连接的结构、分布和频率，以及各种细胞的细胞学特征。根中相邻细胞的原生质体通过不同数量的胞质连接相连：薄壁组织细胞之间有胞间连丝（简单的和分支的）；筛管分子与薄壁组织细胞（西葫芦根中的伴胞、韧皮薄壁细胞或中柱鞘细胞）之间有孔胞间连丝；相邻筛管分子之间有筛域孔。与次生和三生状态内皮层细胞相关的胞间连丝不受栓质层的限制。初生韧皮部、中柱鞘和基本组织的各种细胞类型之间胞质连接的频率存在差异，筛管分子和伴胞之间的频率最高。结果表明，西葫芦根的结构可能与韧皮部卸载并运输到基本组织细胞的共质体途径相适应。
