In the present study, we investigated the effects of tetramethylpyrazine (TMP) on hydrogen peroxide (H2O2)-induced apoptosis in PC12 cells. The apoptosis in H2O2-induced PC12 cells was accompanied by a decrease in Bcl-2/Bax protein ratio, release of cytochrome c to cytosol and the activation of caspase-3. TMP not only suppressed the down-regulation of Bcl-2, up-regulation of Bax and the release of mitochondrial cytochrome c to cytosol, but also attenuated caspase-3 activation and eventually protected against H2O2-induced apoptosis. These results indicated that TMP blocked H2O2-induced apoptosis by the regulation of Bcl-2 family members, suppression of cytochrome c release, and caspase cascade activation in PC12 cells.

Lignin is a natural polymer interlaced with cellulose and hemicellulose in secondary cell walls (SCWs). Auxin acts via its signalling transduction to regulate most of plant physiological processes. Lignification responds to auxin signals likewise and affects the development of anther and secondary xylem in plants. In this review, the research advances of AUXIN RESPONSE FACTOR (ARF)-dependent signalling pathways regulating lignin formation are discussed in detail. In an effort to facilitate the understanding of several key regulators in this process, we present a regulatory framework that comprises protein–protein interactions at the top and protein–gene regulation divided into five tiers. This characterises the regulatory roles of auxin in lignin biosynthesis and links auxin signalling transduction to transcriptional cascade of lignin biosynthesis. Our works further point to several of significant problems that need to be resolved in the future to gain a better understanding of the underlying mechanisms through which auxin regulates lignin biosynthesis.

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