Spatial analysis of the rice leaf growth zone under controlled and cadmium-exposed conditions

Worldwide contamination of agricultural soils with cadmium (Cd) not only leads to reduced plant yield, but accumulation within the edible plant parts also poses a serious threat to human health. In this study, the rice leaf growth zone was used to examine how the effects of Cd on leaf growth are mediated by its effect on cell division and expansion. Based on a kinematic analysis and flow cytometry, we show that both processes are inhibited upon root Cd exposure. The Cd-inhibited leaf growth was confirmed by the overall downregulation of cell cycle genes upon Cd exposure. In addition, Cd preferentially accumulates within the leaf meristem and the transition zone, whereas the concentration steeply drops in the elongation zone. As Cd induces an oxidative challenge, which is also related to plant growth, it was further investigated whether this could be involved in the mode of action of the Cd-inhibited leaf growth. Therefore, gene expression patterns of antioxidative enzymes such as superoxide dismutases (SOD), catalases (CAT) and ascorbate peroxidases (APX) were investigated in different leaf growth zones. Whereas no significant differences were seen for SOD expression across the different leaf zones under control conditions, large differences in abundance were visible for APX and CAT expression. Moreover, Cd stress significantly upregulated genes in these families in an isoform- and location-dependent fashion, indicating the possible involvement of the Cd-induced oxidative challenge in regulating leaf growth processes and highlighting the importance of specific leaf sampling for further investigations.