Surface characteristics and internal structure of Orobanche seedlings
1991
Losner Goshen, D. | Joel, D.M. (Agricultural Research Organization, Newe-Yaar (Israel). Department of Weed Research) | Mayer, A.M. (University of Jerusalem, Jerusalem (Israel). Department of Botany) | Steffens, J.C. (Cornell University, Ithaca, New York (USA). Department of Plant Breeding and Biometry)
The radicle of Orobanche aegyptiaca and O. cumana forms a short, non gravitropic, root which is covered with a thin cuticle. The meristematic cells at the root tip form longitudinal rows that lead to further elongation of the root. The apex is conical, with basipetal gradient of cell maturation. It develops no root cap. As soon as the root tip reaches a host, elongation stops, the apex flattens and a few peripheral cells become papillate. This also happens without any host, then the root tip often turns from conical to roundish as the result of the extension of almost all apical cells. At this stage starch accumulates in the root apex. The papillae surrounding the root tip are cell extensions protruding from epidermal cells. The outer papillar surface often bears wall protuberances of a complex structure. Larger protuberances are located in a more central position, around which small protuberances are scattered, sometimes arranged in concentric circles. The secretory substance, a carbohydrate, accumulates in these protuberances in a sub cuticular space which is encircled with a thick cuticular belt. This substance is released when coming in contact with a host and forms a thin adhesive layer on the papillar surface that binds the parasite to its host. The ultraestructure of the papillar cell is secretory. It shows a dense cytoplasm, abundant with dictyosomes which are arranged in groups. They produce many large secretory vesicles with fibrillar content, presumably related to the secretion of the adhesive carbohydrate
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