ENLARGEMENT AND VACUOLIZATION OF THE CYTOPLASM IN CONTACT CELLS OF RESISTANT AND SUSCEPTIBLE TOMATO PLANTS FOLLOWING INOCULATION WITH FUSARIUM-OXYSPORUM F SP LYCOPERSICI, RACE 1

This study deals with rapid early cytoplasmic responses that occur in contact parenchyma cells that lie immediately adjacent to vascular infections. Earlier studies have shown that such contact cells in tomato and cotton respond to vascular infections by the deposition of apposition wall layers and the synthesis of stress metabolites several hours to several days after inoculation. These responses appear to be part of a complex system of defence. The studies reported here demonstrated that pronounced cytoplasmic changes, which seemingly enable subsequent morphological changes, could be detected 60-90 min after inoculation. The changes included, first, an increased cytoplasmic width (plasmalemma to vacuolar membrane) on the side of the cell proximal to the infection, and later, increased cytoplasmic width on the distal side. No changes in the numbers and/or distribution of mitochondria were detected during this early period. The cytoplasmic response was found to be more rapid and greater in a resistant than in a near-isogenic, susceptible cultivar of tomato. Vacuolization of the cytoplasm was a conspicuous feature associated with this apparent cytoplasm distension. © 1991 Academic Press Limited.