Sensitivity of isolated oat root cap cells and protoplasts to victorin

Abstract

Isolated root cap cells can be used to study the effects of victorin on large populations of intact oat cells. The isolation of oat root cap protoplasts allowed a comparison of victorin-induced death of cells, with or without cell walls. Isolated root cap cells and protoplasts were incubated at 35°C in 0·6 M sorbitol, with or without victorin. Cell or protoplast viability was judged using fluorescein diacetate. Fifty percent of the cells and protoplasts from a susceptible oat cultivar were killed after 10 h in 20 units ml−1 victorin; 50–150 units ml−1 victorin caused 100% death within 6 h. Cells and protoplasts from resistant oat cultivars were not killed by up to 200 units ml−1 victorin. There was no difference in the rate of death of cells with or without cell walls; therefore, the cell wall is not the site of victorin's lethal effects. The root cap cell bioassay was also used to compare the sensitivity of other oat cell types. Root epidermal cells died at the same rate as root cap cells, but root hair and leaf mesophyll cells were at least 10-fold more sensitive to victorin than root cap cells. These results emphasize the need for caution in interpreting pathotoxin studies which employ intact plant tissues that contain a variety of cell types.