Le système endophytique d'Arceuthobium oxycedri. II. Aspects ultrastructuraux des zones de contact entre les tissus de l'hôte et du parasite

Abstract

Ultrastructural study of the contact areas between the endophytic system of Arceuthobium oxycedri and the tissues of its host, Juniperus oxycedrus, shows that a crushed zone often occurs around the large cortical strands and along the primary sinkers in the secondary phloem of the host; such a structure seems rather unfavourable to the transfer of substances. On the other hand, the presence in the secondary xylem of half-bordered pits in direct contact with the cells of the primary and especially secondary sinkers certainly makes it easier for exchanges to take place. At the tip of the sinkers, the cells of the parasite, in the course of their growth, damage the cells of the host and sometimes penetrate into the lumen of its tracheids. Electron microscopy shows important acid phosphatase and ATPase activities at the level of the plasmalemma, plasmodesmata, and also some small endo- or exo-cytotic vesicles in the primary and secondary sinkers. Such activities are a sign of intense active transfer processes in these parts of the endophytic system. Around the contact zones, the parenchymatous cells of the host become very similar in aspect to those of the parasite.