Anatomical Studies of Haustorium Ontogeny and the Remarkable Mode of Penetration of the Haustorium in Nuytsiafloribunda (Labill.) R. Br.

Abstract

AbstractThe development and structure of secondary haustoria of Nuytsia floribunda are described and compared with other Santalalean haustoria.After establishing contact with the host root, cortical folds of the haustorium grow around the root in separate directions and fuse forming a ring around it. At an early stage of development, meristematic tissue differentiates in the interior proximal part of the haustorium. Zones of collapsed layers are present in the outer cortical region. Subsequently, in the proximal part, two vascular cores, two lysigenous cavities and extensive masses of sclerenchyma develop prior to penetration of the host root. The sclerenchymatous cells form a characteristic structure, described as the sclerenchyma prong.During penetration the intrusive part of the haustorium reaches not only the host xylem but continues growing downwards until it entirely splits the host root. Comparable to a guillotine, the sclerenchyma prong is directly involved in this remarkable process. The sclerenchyma prong finally lies in the distal part of the haustorium.Following this mechanical slicing of the host root, tube‐like cells of the intrusive part actively penetrate the host xylem in an axial direction.