Effect of toxic Fe2+ levels on the biological characteristics of rice root border cells

Abstract

Root border cells are a population of rhizosphere cells surrounding the root tips but separated from them. The root tip is a major target of Fe2+ toxicity; thus, it was hypothesized that the border cells might protect or exacerbate Fe2+ toxicity. To explore the effects of excess Fe2+ on the border cells in rice (Oryza sativa L.), experiments were carried out using the border cells in vitro (Shanyou No. 10). The border cells were precultured under “hanging in the air” and detached from the root tips. The shape, numbers, and viability of border cells were examined during exposure to toxic levels of Fe2+. When the root was 1 mm long, there were 205 border cells on average. With the growth of the root, more border cells were observed. When the root grew to 25 mm long, the total number of border cells reached a maximum, while the maximum activity of border cells appeared when the root was 20 mm long. The pectin methyl esterase (PME) activity of the root cap peaked at a root length of 2 mm. Border cell development was related to PME activity in rice. Excessive Fe2+ was toxic to detached border cells. After treatment with 200 μM Fe2+ solution for 48 h, cell viability decreased by 72.70%. However, when treated with 400 μM Fe2+ solution, the number of viable cells was actually higher, suggesting the induction of a cellular self-protection response. The activity of PME first increased under high concentrations of Fe2+ and then decreased. These results indicate that toxic levels of Fe2+ modulate PME activity and border cell survival.