Sécrétions intravasculaires de substances « gommeuses » par les cellules associées aux vaisseaux en réaction à une attaque parasitaire

Differential responses of three grapevine cultivars to Botryosphaeria dieback

Botryosphaeria dieback is a fungal grapevine trunk disease that represents a threat for viticulture worldwide due to the decreased production of affected plants and their premature death. This dieback is characterized by a typical wood discoloration called brown stripe. Herein, a proteome comparison of the brown striped wood from Botryosphaeria dieback-affected standing vines cultivars Chardonnay, Gewurztraminer, and Mourvèdre was performed. The transcript analysis for 15 targeted genes and the quantification of both total phenolics and specific stilbenes were also performed. Several pathogenesis-related proteins and members of the antioxidant system were more abundant in the brown striped wood of the three cultivars, whereas other defense-related proteins were less abundant. Additionally, total phenolics and some specific stilbenes were more accumulated in the brown striped wood. Strongest differences among the cultivars concerned proteins of the primary metabolism, which looked to be particularly impaired in the brown striped wood of 'Chardonnay'. Low abundance of some proteins involved in defense response probably contributes to make global response insufficient to avoid the symptom development. The differential susceptibility of the three grapevine cultivars could be linked to the diverse expression of various proteins involved in defense response, stress tolerance, and metabolism.

Structural modifications induced by Eutypa lata in the xylem of trunk and canes of Vitis vinifera

Eutypa dieback, a devastating disease in grapevines, is caused by the fungal pathogen Eutypa lata, a wood-inhabiting fungus. E. lata acts by degrading wood tissues in the colonisation areas, and produces foliar symptoms. These striking symptoms have been attributed to the production of toxic metabolites by the pathogen, the most widely studied being eutypine. The aims of the study were to compare the effects of E. lata on xylem structure at the site of infection and in remote tissues. In healthy Vitis vinifera, the vessel-associated cells (VACs) in the trunk have a protective layer that covers the entire lignified wall and forms a transfer apparatus in pits located at the VAC / vessel interface. This apparatus occurs similarly in VACs in the basal part of canes but is less developed in the apical part. In the presence of E. lata, which is found only in the trunk and the cordons, the VACs initiated a program of secretory activity that led to the enlargement of the transfer apparatus, which is formed by tightly associated fibrils. This secretory activity was followed by VAC death. Furthermore, the hypertrophy of the transfer apparatus spread according to an acropetal gradient in the canes. Treatment with eutypine also induced the development of the transfer apparatus in VACs of basal and apical parts of canes excised from healthy vines. However, this apparatus was formed by loosely packed fibrils in VACs that were not completely damaged. Therefore, metabolites other than eutypine are expected to be involved in the VAC degeneration observed in infected vines.

Immunocytochemical Evidence that Secretion of Pectin Occurs During Gel (Gum) and Tylosis Formation in Trees

ABSTRACT During gel (gum) formation in angiosperm trees, fibrillar material accumulated in protective layers of xylem parenchyma cells before being secreted across half-bordered pit membranes into vessel elements. Immunogold labeling demonstrated that this fibrillar material was mainly composed of partially esterified pectic polysaccharides. The primary wall of expanding tyloses, an extension of the parenchyma protective layer, secreted similar pectic substances to completely block vessel elements. In most studies, these occluding structures were reported to be formed in response to causative factors such as aging processes, injuries, or infections. Current observations support the view that partial to complete embolism, which almost always accompanies these factors, might be the main cause triggering the formation of vessel occlusions. Whereas pectin seems to be the basic component of gels (gums) and of the external layer of tyloses, other substances, such as phenols, were also detected either as a part of these plugs or as accumulations beside them in vessels. Finally, it is proposed that the term 'gel' instead of 'gum' be used in future studies to describe the occluding material secreted by ray and paratracheal parenchyma cells.

Secretory tissues in vascular plants

Secretory tissues occur in most vascular plants. Some of these tissues, such as hydathodes, salt glands and nectaries, secrete unmodified or only slightly modified substances supplied directly or indirectly by the vascular tissues. Other tissues secreting, for instance, polysaccharides, proteins and lipophilic material, produce these substances in their cells. The cells of secretory tissues usually contain numerous mitochondria. The frequency of other cell organelles varies according to the material secreted. In most glandular trichomes the side wall of the lowest stalk cell is completely cutinized. This prevents the secreted material from flowing back into the plant. The salt glands in Atriplex eliminate salt into the central vacuole of the bladder cell but, in other plants, the glands secrete salt to the outside. Different views exist as to the manner in which salt is eliminated from the cytoplasm. According to some authors, the mode of elimination is an eccrine one, while others suggest the involvement of membrane-bound vesicles. Nectar is of phloem origin. The pre-nectar moves to the secretory cells through numerous plasmodesmata present in the nectariferous tissue. Nectar is eliminated from the secretory cells by vesicles of either KR or dictyosomal origin. In some cases, both organelles may be involved but an eccrine mode of nectar secretion has also been suggested by some authors. Carbohydrate mucilages and gums are synthesized by dictyosomes but virtually every cell compartment has been suggested as having a role on the secretion of lipophilic substances. Most commonly, plastids are implicated in the synthesis of lipophilic materials but KR may also play a part. In some cases lipophilic materials may be transported towards the plasmalemma in the KR. Resin and gum ducts of some plants develop normally or in response to external stimuli, such as microorganisms or growth substances. Among the latter, ethylene is the most effective. During the course of evolution, secretory tissues seem to have developed from secretory idioblasts scattered among the cells of the ordinary tissues. Subsequently ducts and cavities developed and finally secretory trichomes. CONTENTS Summary 229 I. Introduction 230 II. Salt glands 231 III. Nectaries 236 IV. Mucilages and gums 241 V. Tissues secreting lipophilic material 242 VI. Factors influencing the development of certain secretory tissues 246 VII. Evolutionary considerations 248 References 250.