J Plant Res (2006) 119:337–342 © The Botanical Society of Japan and Springer-Verlag Tokyo 2006 Digital Object Identifier (DOI) 10.1007/s10265-006-0278-y Springer-VerlagTokyohttp://www.springer.de102650918-94401618-0860Journal of Plant ResearchJ Plant ResLife Sciences27810.1007/s10265-006-0278-y Involvement of inorganic elements in tissue reunion in the hypocotyl cortex of Cucumis sativus REGULAR PAPER Received: October 26, 2005 / Accepted: March 7, 2006 / Published online: May 11, 2006 The Botanical Society of Japan and Springer-Verlag 2006 Masashi Asahina • Yuriko Gocho • Hiroshi Kamada • Shinobu Satoh M. Asahina · Y. Gocho · H. Kamada · S. Satoh (* ) Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8572, Japan Tel. +81-298-534871; Fax +81-298-534579 e-mail: satohshi@sakura.cc.tsukuba.ac.jp Abstract Cucumber (Cucumis sativus L.) hypocotyls were transversely cut to half their diameter, and morphological analyses of the tissue-reunion process in the cortex were conducted to elucidate the involvement of root-derived fac- tors. Cell division in the cortex commenced 3 days after cutting, and the cortex was nearly fully united within 7 days. In shoots from which the roots were removed and which were cultured in water, cell division occurred during tissue reunion; however, thick-wall layer formed in the reunion region, and intrusive cell elongation and interdigitation of cortex cells at the cut surface did not occur, even after 7 days. Interdigitation of cells, followed by normal tissue reunion, was observed in shoots from which the roots were removed and which were cultured in squash xylem sap or Murashige and Skoog (MS) medium. The same effect was observed with the simultaneous application of B, Mn, and Zn, which are the major inorganic microelements of MS medium. Our results suggest that application of these inor- ganic elements, which are taken up from the soil and trans- ferred to the xylem sap, are required for interdigitation of cells during tissue reunion in the cortex of cucumber hypo- cotyls, possibly because they are required for cell wall func- tion and metabolism. Key words Inorganic elements · Interdigitation of cells · Murashige and Skoog medium · Root · Tissue-reunion of cut hypocotyl · Xylem sap and aboveground organs are connected by xylem and phloem in vascular bundles, and vascular tissues provide long-distance transport of water, nutrients, and various organic and inorganic materials within the plant (Jesko 1989; Satoh et al. 1998; Sakuta and Satoh 2000). When the original vascular connection is interrupted by wounding or grafting, the formation of new vascular tissue should be induced. Although the molecular mechanisms controlling vascular reunion are not yet fully understood, the involve- ment of phytohormones such as auxin and cytokinin, in xylem and phloem differentiation has been suggested (Roberts 1988; Mattsson et al. 1999; Sachs 2000). Studies of graft union and repair in cut tissues have focused on the differentiation of vascular elements in the tissue-reunion process, but the process of reunion in the cortex of cut tissues is not well understood. Our previous study of tissue reunion in cucumber and tomato seedlings showed that the division and elongation of cortex cells begins at 3 days after cutting, and that the cortex is nearly completely united within 7 days (Asahina et al. 2002). Gibberellin (GA) is required for cell division during tissue reunion in the cortex of cut hypocotyls, and cotyledons are involved in GA production (Asahina et al. 2002). In contrast, in plants from which the roots are removed and the shoot is cultured in water, cell division occurs during tissue reunion, but intrusive cell elongation and the inter- digitation of cells between confronted cut cortex cells does not occur, even after 7 days. The interdigitation of cells during tissue reunion may play a role in the re-generation of the physiological and physical connections between sep- arated tissues and cells. Such connections include intercel- lular attachment through the cell wall. Plant cell walls are composed primarily of cellulose microfibrils, hemicellulose, pectic polysaccharides, and small amounts of structural proteins (Carpita et al. 1993; Ridley et al. 2001; Willats et al. 2001). Pectin is thought to be involved in intercellular attachment because it is local- ized mainly in the primary cell wall, middle lamella, and cell corners. Pectin consists mainly of three structurally charac- terized polysaccharides: homogalacturonans (HGs) and Asahina M and Gocho Y equally contributed to this work. Introduction In higher plants, growth is thought to depend on interac- tions among organs such as roots, shoots, and leaves. Roots