EFFECTS OF NONGLYCOSYLATED AND GLYCOSYLATED POLYPEPTIDES SECRETED BY THE GRAPEVINE PATHOGEN EUTYPA LATA ON THE STRUCTURAL FEATURES AND MEMBRANE PROCESSES IN GRAPEVINE CELLS
S. Octave, G. Roblin, P. Fleurat-Lessard
Eutypa dieback is a devastating disease of Vitis vinifera L. caused by the fungal pathogen Eutypa lata (Pers.: Fr.) Tul. et C. Tul., which colonizes the vascular tissues of the trunk. Symptoms observed in developing shoots and in the foliage indicate that a necrotic signal spreads at a distance from the infected area. Previous studies have shown that toxic polypeptides isolated from E. lata cultures are able to induce some modifications typical of the disease observed in grapevines. The main aim of this study was to investigate the biological effects of polypeptide sub-fractions (glycosylated and non-glycosylated) for determining the mode and site of action of these toxic compounds. Compounds in the non-glycosylated fraction induced leaf necrosis, increased vacuolar tannin synthesis, modified mitochondria, but induced only a partial damage of the cell wall. They hindered the H+ flux and nutrient uptake as a result of the modification of H+ gradient, as seen on plasma membrane vesicles, without affecting the H+-ATPase activity. Eutypine induced the same effects (i.e. on mitochondria and protonophoric action). Polypeptides of the glycosylated fraction increased anthocyanin synthesis in isolated leaves, promoted the decrease of the starch content and casused heavy damage to the cell wall. They also modified H+ flux and nutrient uptake but, in this case, these processes may be the consequence of a direct effect on the H+-ATPase activity. Our results show that the different toxic compounds secreted by E. lata present a complex frame of action on various plant cellular sites. These effects impair plant metabolism and damage cell structure thus favouring host invasion by the fungus.