RESISTANCE OF YOUNG VERSUS OLD TOBACCO-LEAVES TO NECROTROPHS, FUSARIC ACID, CELL WALL-DEGRADING ENZYMES AND AUTOLYSIS OF MEMBRANE-LIPIDS

Infection with necrotrophs, Alternaria alternata or Botrytis cinerea caused more severe symptoms on old than young tobacco leaves. Much higher amounts of fusaric acid were required to induce necrosis in young leaves compared with older leaves. Similarly fusaric acid caused higher leakage of ions from older leaf discs than from younger discs. Leaf slices from younger leaves were more resistant to pectinase and cellulase enzymes. Protoplasts from younger leaves were more tolerant to the toxic effect of cell wall-degrading enzymes than protoplasts from older leaves. These differences were related to lipid content. The amount of phospho- and galactolipids was higher while the amount of free sterols was lower in juvenile leaf tissues. The autolysis of phospholipids was much higher in homogenates from older leaves, suggesting that infection caused cell decompartmentalization resulting from a more rapid degradation of membranes in senescent tissues compared to young leaves. © 1992.