The structure and development of the haustorium in Cuscuta australis

Abstract

The structure and development of the haustorium of a parasitic angiosperm Cuscuta australis R. Brown growing on the host plant Trifolium repens L. was studied with light and electron microscopy. The upper haustorium, which lies external to the host organ, initiates endogenously from cortical cells of the middle layers of the parasite stem. The initial cells develop into a group of meristematic cells. As haustorial maturation progresses, the meristematic cells develop into an endophyte primordium that penetrates the host tissue. The endophyte primordium consists of three cell types: (i) remarkably enlarged elongate cells (digitate cells) with very dense cytoplasm and large nuclei at the central region; (ii) smaller file cells with prominent nuclei proximal to the digitate cells; and (iii) highly compressed cells distal to the digitate cells. Evidence suggests that the digitate cells are metabolically very active. The endophyte, which lies internal to the host tissue, consists of parenchymatous axial cells and elongate tip cells with dense cytoplasm and conspicuous nuclei. The axial and tip cells of endophyte are interpreted as originating from the file and digitate cells of the endophyte primordium, respectively. The tip cells independently penetrate the host tissues and transform into the filamentous hyphae. The hyphae reach the host vascular tissues and eventually differentiate into xylary or phloic conductive hyphae.

Interspecific RNA Interference of SHOOT MERISTEMLESS-Like Disrupts Cuscuta pentagona Plant Parasitism

“…Previous literature interprets the dodder haustorium as a highly modified adventitious root (Truscott, 1958;Kuijt, 1976;Lee and Chai, 1989;Lee, 2007). Ultrastructural analysis of the origin of adventitious roots in cuttings of the distant relative petunia (Petunia hybrida) show their origin from cell divisions within the cambium layer itself (Ahkami et al, 2009) in a manner distinct from the dedifferentiation of cortical parenchyma in dodder.…”

The biology of Canadian weeds. 133. Cuscuta campestris Yuncker, C. gronovii Willd. ex Schult., C. umbrosa Beyr. ex Hook., C. epithymum (L.) L. and C. epilinum Weihe.

“…The mechanism of attachment and the development of haustoria have been studied in detail from a structural perspective (Kuijt and Toth 1976;Lee and Lee 1989;Dawson et al 1994;Vaughn 2002Vaughn , 2003. Haustoria develop on the inner (concave) side of the stem coils and their part that will remain external to the host is called prehaustorium ("upper haustorium"- Lee and Lee 1989;or "adhesive disk"-Dawson et al 1994).…”

“…Haustoria develop on the inner (concave) side of the stem coils and their part that will remain external to the host is called prehaustorium ("upper haustorium"- Lee and Lee 1989;or "adhesive disk"-Dawson et al 1994). The prehaustorium develops endogenously from a disk-like meristem located within the cortex, close to the vascular bundles (Dawson et al 1994).…”

“…Haustoria invasion and connection to the vascular system of the host -Mechanisms of connection to the host have been studied in great detail (Kuijt and Toth 1976;Lee and Lee 1989;Dawson et al 1994;Vaughn 2002Vaughn , 2003. After the successful contact and attachment of the parasite, a mass of tissue known as the "inner haustorium" penetrates and invades the host tissue.…”

Anatomy and ultrastructure of epidermal cells in the haustorium of a parasitic flowering plant,Cuscuta japonica, during attachment to the host

“…Thus the attachment mechanism(s) of the upper haustoria are not known in detail. Field and laboratory investigations have found that many haustoria fail to make functional attachments (Baird and Riopel, 1983;Lee and Lee, 1989;Lesny, 1991). In several parasites, this contact is undoubtedly promoted by the tight adhesion of the upper haustoria to the host surface, thereby reinforcing the subsequent thrust of the invading endophyte (Riopel and Timko, 1995).…”