Gamma-tubulin distribution and ultrastructural changes in root cells of soybean (Glycine max L.) seedlings under cadmium stress

Abstract

Gamma-tubulin (γ-tubulin) is known to be a key component of the complexes responsible for nucleation and the provision of spatial and temporal control over the functioning of the microtubule cytoskeleton. However, the effect of heavy metal stress on the distribution of γ-tubulin containing complexes has not yet been elucidated. In this study, we present the effect of cadmium (Cd) on γ-tubulin distribution in plant cells. The localization and level of γ-tubulin was assessed in the root cells of soybean seedlings exposed to moderate (85μM) and high (170μM) Cd concentrations, using various immunological approaches. In response to Cd, the fluorescence signal for γ-tubulin was significantly weaker. This decrease was most pronounced in the neighborhood of the nuclei envelope and plasmalemma of interphase cells and in the mitotic arrays of dividing cells. This finding was in line with a biochemical analysis which revealed that Cd leads to a decrease in the level of some γ-tubulin isoforms and the appearance of low molecular γ-tubulin-related proteins. Interestingly, at the same time, exposure to Cd at high concentration resulted in the up-regulation of γ-tubulin encoding genes. The results indicate that Cd stress might provoke dysfunctionality in γ-tubulin complexes, which contribute to a disturbed MT cytoskeleton structure. Additionally, ultrastructural observations confirmed considerable Cd-dependent subcellular changes in the root cells of soybean seedlings. The most prominent of these included vacuolization of the cytoplasm, occurrence of autophagic bodies and electron dense deposits in the vacuole, changes in the nucleolus structure and callose deposition. The observed changes are discussed as a response to stress conditions.