The histidine phosphotransfer AHP4 plays a negative role in Arabidopsis plant response to drought.

Cytokinin plays an important role in plant stress responses via a multistep signaling pathway, involving the histidine phosphotransfer proteins (HPs). In Arabidopsis thaliana, the AHP2, AHP3 and AHP5 proteins are known to affect drought responses; however, the role of AHP4 in drought adaptation remains undetermined. In the present study, using a loss-of-function approach we showed that AHP4 possesses an important role in the response of Arabidopsis to drought. This is evidenced by the higher survival rates of ahp4 than wild-type (WT) plants under drought conditions, which is accompanied by the downregulated AHP4 expression in WT during periods of dehydration. Comparative transcriptome analysis of ahp4 and WT plants revealed AHP4-mediated expression of several dehydration- and/or abscisic acid-responsive genes involved in modulation of various physiological and biochemical processes important for plant drought acclimation. In comparison with WT, ahp4 plants showed increased wax crystal accumulation in stems, thicker cuticles in leaves, greater sensitivity to exogenous abscisic acid at germination, narrow stomatal apertures, heightened leaf temperatures during dehydration, and longer root length under osmotic stress. In addition, ahp4 plants showed greater photosynthetic efficiency, lower levels of reactive oxygen species, reduced electrolyte leakage and lipid peroxidation, and increased anthocyanin contents under drought, when compared with WT. These differences displayed in ahp4 plants are likely due to upregulation of genes that encode enzymes involved in reactive oxygen species scavenging and non-enzymatic antioxidant metabolism. Overall, our findings suggest that AHP4 plays a crucial role in plant drought adaptation.

Comparison of safety of subcutaneous enoxaparin as outpatient anticoagulation bridging therapy in patients with a mechanical heart valve versus patients with nonvalvular atrial fibrillation.

Patients with mechanical heart valves (MHVs) are at a higher risk for thromboembolic events than patients with atrial fibrillation (AF). This difference is observed in the higher maintenance international normalized ratio (INR) range for patients with MHV and in the selection for anticoagulation bridge therapy when warfarin is interrupted perioperatively. However, once the decision is made to "bridge," the same therapeutic options, unfractionated heparin and subcutaneous low-molecular-weight heparin (LMWH), are applicable to the 2 patient populations. Unfractionated heparin requires extended hospitalization and is often not selected. A paucity of published data exist establishing the efficacy and safety of LMWH as a bridging agent. The aim of this study was to describe a single-center experience and to provide data supporting the use of enoxaparin as a bridging agent. The study assessed whether patients with MHV undergoing bridging for a variety of procedures had higher thromboembolic and hemorrhagic risk compared to patients with nonvalvular AF. We performed a retrospective cohort study of 173 patients (with MHV and AF) who underwent 230 bridging episodes with an LMWH, enoxaparin, from February 2002 through September 2007. Main outcome measurements were the incidence of thromboembolic and hemorrhagic events within 2 months after the procedure. Of total bridging episodes, 130 episodes met the inclusion criteria; 62 episodes occurred in the MHV population and 68 episodes occurred in the AF population. The procedures varied from minor invasive procedures to major surgeries. There were no deaths or thromboembolic events. Major and minor bleeding rates were similar between the MHV and AF groups (3.2% and 2.9%, 14.5% and 13.2% respectively, p = NS). The major bleeding rate was similar to published data on bridging therapy. Most bleeding episodes (73%) occurred within 7 days after the procedure. In conclusion, our study provided actual outpatient anticoagulation clinical data on using LMWH as an option for periprocedural bridging anticoagulation in patients with MHV.