Boron Nutrition of Tobacco BY-2 Cells. V. Oxidative Damage is the Major Cause of Cell Death Induced by Boron Deprivation

Boron (B) is an essential micronutrient for vascular plants. However, it remains unclear how B deficiency leads to various metabolic disorders and cell death. To understand this mechanism, we analyzed the physiological changes in suspension-cultured tobacco (Nicotiana tabacum) BY-2 cells upon B deprivation. When 3-day-old cells were transferred to B-free medium, cell death was detectable as early as 12 h after treatment. The B-deprived cells accumulated more reactive oxygen species and lipid peroxides than control cells, and showed a slight but significant decrease in the cellular ascorbate pool. Supplementing the media with lipophilic antioxidants effectively suppressed the death of B-deprived cells, suggesting that the oxidative damage is the immediate and major cause of cell death under B deficiency. Dead cells in B-free culture exhibited a characteristic morphology with a shrunken cytoplasm, which is often seen in cells undergoing programmed cell death (PCD). However, they did not display other hallmarks of PCD such as internucleosomal DNA fragmentation, decreased ascorbate peroxidase expression and protection from death by cycloheximide. These results suggest that the death of tobacco cells induced by B deprivation is not likely to be a typical PCD.