Simultaneous recording of diurnal changes in leaf turgor pressure and stem water status of bread wheat reveal variation in hydraulic mechanisms in response to drought.

Information about water relations within crop canopies is needed to improve our understanding of canopy resource distribution and crop productivity. In this study, we examined the dehydration/rehydration kinetics of different organs of wheat plants using ZIM-probes that continuously monitor water status non-destructively. ZIM-probes were clamped to the flag leaf and penultimate leaf of the same stem to monitor changes in turgor pressure, and a novel stem probe was clamped to the peduncle (just below the spike of the same stem) to monitor changes in stem water status. All organs behaved similarly under well-watered conditions, dehydrating and recovering at the same times of day. When water was withheld, the behaviour diverged, with the leaves showing gradual dehydration and incomplete recovery in leaf turgor pressure during the night, but the stem was affected to a lesser extent. Penultimate leaves were the most severely affected, reaching turgor loss point before the flag leaf. Upon rewatering, turgor pressure recovered but the output patch-pressure of the probes (Pp) oscillated at ~30min periods in all organs of most plants (n=4). Oscillations in Pp were attributed to oscillations in stomatal opening and appear to only occur above a threshold light intensity. The mechanisms identified in this study will be beneficial for crop productivity because the flag leaf is the source of most photoassimilates in developing grains, so the plant's ability to maintain flag leaf hydration at the expense of older leaves should moderate the impact of drought on yield. Stomatal oscillations could increase water use efficiency as the plant attempts to rehydrate after drought.

Spatio-temporal water dynamics in mature Banksia menziesii trees during drought.

Southwest Australian Banksia woodlands are highly diverse plant communities that are threatened by drought- or temperature-induced mortality due to the region's changing climate. We examined water relations in dominant Banksia menziesii R. Br. trees using magnetic leaf patch clamp pressure (ZIM-) probes that allow continuous, real-time monitoring of leaf water status. Multiple ZIM-probes across the crown were complemented by traditional ecophysiological measurements. During summer, early stomatal downregulation of transpiration prevented midday balancing pressures from exceeding 2.5 MPa. Diurnal patterns of ZIM-probe and pressure chamber readings agreed reasonably well, however, ZIM-probes recorded short-term dynamics, which are impossible to capture using a pressure chamber. Simultaneous recordings of three ZIM-probes evenly spaced along leaf laminas revealed intrafoliar turgor gradients, which, however, did not develop in a strictly basi- or acropetal fashion and varied with cardinal direction. Drought stress manifested as increasing daily signal amplitude (low leaf water status) and occasionally as rising baseline at night (delayed rehydration). These symptoms occurred more often locally than across the entire crown. Microclimate effects on leaf water status were strongest in crown regions experiencing peak morning radiation (East and North). Extreme spring temperatures preceded the sudden death of B. menziesii trees, suggesting a temperature- or humidity-related tipping point causing rapid hydraulic failure as evidenced by collapsing ZIM-probe readings from an affected tree. In a warmer and drier future, increased frequency of B. menziesii mortality will result in significantly altered community structure and ecosystem function.

Safety evaluation of the concomitant use of clozapine and benzodiazepines: a retrospective, cross-sectional chart review.

OBJECTIVE: Previously published case reports have noted severe adverse reactions such as cardiac arrest, respiratory arrest, and sudden death when clozapine (CLZ) and benzodiazepines (BZDs) are used concomitantly. As CLZ and BZD are both used regularly to treat psychiatric illness, it is important to have additional information concerning this potential interaction. The objective of this study was to contribute to the evolving literature by evaluating the occurrence of sudden deaths and cardiac or respiratory events leading to death in patients treated concurrently with CLZ and BZD. METHOD: A retrospective chart review was conducted at a 240-bed New York State mental health facility. Most patients in this facility have been diagnosed with refractory schizophrenia, resulting in high rates of CLZ use. Electronic and hard copy records of the 490 patients who had been treated with CLZ in this facility at any time from 2001 to 2006 were selected, and the medication records of these patients were assessed for concomitant BZD use. Information on 152 patients who were treated with CLZ and a BZD concomitantly during this time period are included in this study. Data from the facility's mortality review committee were obtained to determine sudden deaths and cardiac or respiratory events leading to death in patients treated with CLZ and BZD concomitantly. Secondary parameters also recorded during the chart review included average duration of CLZ therapy, BZD therapy, and concomitant therapy; average doses of agents used; specific BZD used; number of patients treated with a specific BZD; psychiatric diagnosis; and use of other medications that depress the central nervous system. RESULTS AND CONCLUSIONS: No deaths occurred as a result of concomitant BZD and CLZ use in the sample examined in this study, suggesting that CLZ and BZD may be safely used concomitantly in many cases. Further study is needed to determine patient characteristics or predisposing factors that might put patients at higher risk of death from this interaction. Our findings are limited by the small sample size and suboptimal frequency of side effect measurements (e.g., measurements of blood pressure and heart rate, reports of hypotensive episodes). Confounding variables that might also play a role in interactions between CLZ and BZDs, but which were not measured in this study, include other types of respiratory compromise, cognitive dysfunction, and organ dysfunction. Precautionary measures that may be used when initiating concomitant CLZ and BZD therapy include slow titration of CLZ, blood pressure monitoring, and/or nightly pulse oximeter measurements.

Methamphetamine administration reduces hippocampal vesicular monoamine transporter-2 uptake.

Repeated high-dose injections of methamphetamine (METH) rapidly decrease dopamine uptake by the vesicular monoamine transporter-2 (VMAT-2) associated with dopaminergic nerve terminals, as assessed in nonmembrane-associated vesicles purified from striata of treated rats. The purpose of this study was to determine whether METH similarly affects vesicular uptake in the hippocampus; a region innervated by both serotonergic and noradrenergic neurons and profoundly affected by METH treatment. Results revealed that repeated high-dose METH administrations rapidly (within 1 h) reduced hippocampal vesicular dopamine uptake, as assessed in vesicles purified from treated rats. This reduction was likely associated with serotonergic nerve terminals because METH did not further reduce vesicular monoamine uptake in para-chloroamphetamine-lesioned animals. Pretreatment with the serotonin transporter inhibitor fluoxetine blocked both this acute effect on VMAT-2 and the decrease in serotonin content observed 7 days after METH treatment. In contrast, there was no conclusive evidence that METH affected vesicular dopamine uptake in noradrenergic neurons or caused persistent noradrenergic deficits. These findings suggest a link between METH-induced alterations in serotonergic hippocampal vesicular uptake and the persistent hippocampal serotonergic deficits induced by the stimulant.