The effects of silicon application before sowing on the drought-induced oxidative stress and antioxidant defense in wheat (Triticum aestivum L.) were investigated. Drought stress was applied by withholding watering till sampling at booting or filling stage. Application of Si increased the water potential of drought-stressed plants at filling stage, whereas it did not at booting stage. The superoxide dismutase (SOD) activity was inhibited and peroxidase (POD) activity was enhanced by drought at booting stage, and no differences were observed due to the Si treatment. At filling stage, however, application of Si increased the SOD activity and decreased the POD activity of drought-stressed plants. The catalase (CAT) activity was slightly increased by drought only in the absence of Si and at booting stage. The activity of glutathione reductase (GR) was not greatly influenced. Application of Si did not change the contents of H 2 O 2 , total soluble protein and protein carbonyl of drought-stressed plants at booting stage, whereas at filling stage, it decreased the content of H 2 O 2 and protein carbonyl and increased the content of total soluble protein. The content of thiobarbituric acid reactive substances (TBARS) and the activities of acid phospholipase (AP) and lipoxygenase (LOX) in drought-stressed plants were also decreased by application of Si at both stages.

Death-associated protein kinase (DAPK) is a key player in several modes of neuronal death/injury and has been implicated in the late-onset Alzheimer's disease (AD). DAPK promotes cell death partly through its effect on regulating actin cytoskeletons. In this study, we report that DAPK inhibits microtubule (MT) assembly by activating MARK/PAR-1 family kinases MARK1/2, which destabilize MT by phosphorylating tau and related MAP2/4. DAPK death domain, but not catalytic activity, is responsible for this activation by binding to MARK1/2 spacer region, thereby disrupting an intramolecular interaction that inhibits MARK1/2. Accordingly, DAPK À/À mice brain displays a reduction of tau phosphorylation and DAPK enhances the effect of MARK2 on regulating polarized neurite outgrowth. Using a well-characterized Drosophila model of tauopathy, we show that DAPK exerts an effect in part through MARK Drosophila ortholog PAR-1 to induce rough eye and loss of photoreceptor neurons. Furthermore, DAPK enhances tau toxicity through a PAR-1 phosphorylation-dependent mechanism. Together, our study reveals a novel mechanism of MARK activation, uncovers DAPK functions in modulating MT assembly and neuronal differentiation, and provides a molecular link of DAPK to tau phosphorylation, an event associated with AD pathology.