Heo Jung-Ok, Roszak Pawel, Furuta Kaori M, Helariutta Ykä
Institute of Biotechnology, Department of Bio and Environmental Sciences, University of Helsinki, FIN-00014, Finland.
Am J Bot. 2014 Sep;101(9):1393-402. doi: 10.3732/ajb.1400197. Epub 2014 Sep 2.
Phloem, as a major tissue mediating long-distance communication, has been an object of extensive research ever since its structure was first reported in 1837. Functional phloem consists of sieve elements (SEs) and companion cells (CCs). While SEs are enucleated conducting cells in the phloem, CCs are cells with intact cellular components and are known to support the functioning of SEs. CCs are closely linked to SEs by symplastic connections mediated by plasmodesmata (PD). Sieve elements are notoriously sensitive to manipulation, which has hampered efforts to investigate their structure using microscopy or histology; phloem thus remains a mysterious tissue almost 200 yr after its discovery. Nevertheless, consistent efforts have overcome many of the technical barriers and generated considerable amounts of data about the structure and function of phloem. Advances in the 1950s and 1960s significantly improved our understanding of phloem anatomy and function. A major function of the phloem is to establish symplastic connections throughout the plant body, delivering nutrients and various signaling molecules, which play pivotal roles in growth and development. Despite the importance of phloem, details about the molecular mechanisms responsible for the establishment and maintenance of phloem continuity remain elusive.
韧皮部作为介导长距离通讯的主要组织，自1837年首次报道其结构以来，一直是广泛研究的对象。功能性韧皮部由筛管分子（SEs）和伴胞（CCs）组成。筛管分子是韧皮部中无细胞核的传导细胞，而伴胞是具有完整细胞成分的细胞，已知其支持筛管分子的功能。伴胞通过胞间连丝（PD）介导的共质体连接与筛管分子紧密相连。筛管分子对操作极其敏感，这阻碍了利用显微镜或组织学研究其结构的努力；因此，韧皮部在被发现近200年后仍然是一个神秘的组织。尽管如此，持续的努力克服了许多技术障碍，并产生了大量关于韧皮部结构和功能的数据。20世纪50年代和60年代的进展显著提高了我们对韧皮部解剖结构和功能的理解。韧皮部的一个主要功能是在整个植物体内建立共质体连接，输送营养物质和各种信号分子，这些分子在生长和发育中起着关键作用。尽管韧皮部很重要，但负责韧皮部连续性建立和维持的分子机制的细节仍然难以捉摸。
