Changes in the cytoskeleton accompanying infection-induced nuclear movements and the hypersensitive response in plant cells invaded by rust fungi

Abstract

During the infection of cowpea (Vigna unguiculata) by the cowpea rust fungus (Uromyces vignae, race 1) the plant nucleus moves towards and away from the invading hypha and eventually moves close to the fungus in the susceptible cultivar while it remains away in two cultivars which subsequently respond by resistance gene-dependent plant cell death (the hypersensitive response, HR). The role of plant cytoskeleton in these responses was investigated by fluorescent microscopy and treatments with anticytoskeletal drugs. Observations of microtubule organization prior to cell death revealed that the sequence of events leading to protoplast collapse differed between the two resistant cultivars, suggesting a possibility of multiple pathways for cellular degradation during the HR. Different fixations produced two different microfilament patterns: a filament network and cables. Microfilament network remained visible even at later stages of cell death. Oryzalin and taxol reduced the incidence of autofluorescence that develops late in the death process, indicating a role of microtubules in the deposition of phenolics by adjacent living cells. Cell death and nuclear movements were not affected by oryzalin and taxol but were inhibited by cytochalasin E, suggesting that the microfilaments are required for the HR.