Xylem structure and hydraulic characteristics of deep roots, shallow roots and branches of walnut under seasonal drought.

BACKGROUND: Despite the importance of root hydraulics, there is little research on the in situ dynamic responses of embolism formation and embolism repair of roots distributed in different soil depths in response to different water regimes. RESULTS: The vessel diameter, hydraulic conductivity, and vulnerability to cavitation were in the order of deep root > shallow root > branch. The midday PLC of shallow root was the highest in the dry season, while the midday PLC of deep root slightly higher than that of branch with no significant difference in the two seasons. The capacity of embolism repair of roots was significantly greater than that of branch both in dry season and wet season. The xylem pressure was in the order of deep roots > shallow root > branch, and it was negative in most of the time for the latter two in the dry season, but positive for both of the roots during the observation period in the wet season. The NSC and starch content in roots were significantly higher than those in branches, especially in the dry season. In contrast, roots had lower content of soluble sugar. CONCLUSIONS: The relatively stable water condition in soil, especially in the deep layers, is favorable for the development of larger-diameter vessels in root xylem, however it cannot prevent the root from forming embolism. The mechanism of embolism repair may be different in different parts of plants. Deep roots mainly depend on root pressure to refill the embolized vessels, while branches mainly depend on starch hydrolysis to soluble sugars to do the work, with shallow roots shifted between the two mechanisms in different moisture regimes. There is theoretically an obvious trade-off between conducting efficiency and safety over deep roots, shallow roots and branches. But in natural conditions, roots do not necessarily suffer more severe embolism than branches, maybe due to their root pressure-driven embolism repair and relatively good water conditions.

Cell-Permeable Peptide Targeting the Nrf2-Keap1 Interaction: A Potential Novel Therapy for Global Cerebral Ischemia.

The current study examined efficacy of a small Tat (trans-activator of transcription)-conjugated peptide activator of the Nrf2 (nuclear factor-E2-related factor-2) antioxidant/cell-defense pathway as a potential injury-specific, novel neuroprotectant against global cerebral ischemia (GCI). A competitive peptide, DEETGE-CAL-Tat, was designed to facilitate Nrf2 activation by disrupting interaction of Nrf2 with Keap1 (kelch-like ECH-associated protein 1), a protein that sequesters Nrf2 in the cytoplasm and thereby inactivates it. The DEETGE-CAL-Tat peptide contained the critical sequence DEETGE for the Nrf2-Keap1 interaction, the cell transduction domain of the HIV-Tat protein, and the cleavage sequence of calpain, which is sensitive to Ca(2+) increase and allows injury-specific activation of Nrf2. Using an animal model of GCI, we demonstrated that pretreatment with the DEETGE-CAL-Tat peptide markedly decreased Nrf2 interaction with Keap1 in the rat hippocampal CA1 region after GCI, and enhanced Nrf2 nuclear translocation and DNA binding. The DEETGE-CAL-Tat peptide also induced Nrf2 antioxidant/cytoprotective target genes, reduced oxidative stress, and induced strong neuroprotection and marked preservation of hippocampal-dependent cognitive function after GCI. These effects were specific as control peptides lacked neuroprotective ability. Intriguingly, the DEETGE-CAL-Tat peptide effects were also injury specific, as it had no effect upon neuronal survival or cognitive performance in sham nonischemic animals. Of significant interest, peripheral, postischemia administration of the DEETGE-CAL-Tat peptide from days 1-9 after GCI also induced robust neuroprotection and strongly preserved hippocampal-dependent cognitive function. Based on its robust neuroprotective and cognitive-preserving effects, and its unique injury-specific activation properties, the DEETGE-CAL-Tat peptide represents a novel, and potentially promising new therapeutic modality for the treatment of GCI. SIGNIFICANCE STATEMENT: The current study demonstrates that DEETGE-CAL-Tat, a novel peptide activator of a key antioxidant gene transcription pathway in the hippocampus after global cerebral ischemia, can exert robust neuroprotection and preservation of cognitive function. A unique feature of the peptide is that its beneficial effects are injury specific. This feature is attractive as it targets drug activation specifically in the site of injury, and likely would lead to a reduction of undesirable side effects if translatable to the clinic. Due to its injury-specific activation, robust neuroprotection, and cognitive-preserving effects, this novel peptide may represent a much-needed therapeutic advance that could have efficacy in the treatment of global cerebral ischemia.

Maintenance of xylem hydraulic function during winter in the woody bamboo Phyllostachys propinqua McClure.

Background: Frost is a common environmental stress for temperate plants. Xylem embolism occurs in many overwintering plants due to freeze-thaw cycles, so coping with freeze-thaw-induced embolisms is essential for the survival of temperate plants. Methods: This study was conducted on Phyllostachys propinqua McClure, a woody bamboo species that was grown under natural frost conditions to explore its responses to winter embolisms. From autumn to the following spring, the following measurements were recorded: predawn branch and leaf embolism, branch and leaf relative water content (RWC), root pressure and soil temperature, xylem sap osmotic potential, branch and leaf electrolyte leakage (EL), branch nonstructural carbohydrate (NSC) content and leaf net photosynthetic rate. Results: P. propinqua had a mean vessel diameter of 68.95 ±1.27 µm but did not suffer severe winter embolism, peaking around  60% in winter (January), with a distinct reduction in March when root pressure returned. Leaves had a more severe winter embolism, up to 90%. Leaf RWC was much lower in winter, and leaf EL was significantly higher than branch EL in all seasons. Root pressure remained until November when soil temperature reached 9 °C, then appeared again in March when soil temperatures increased from -6 °C (January) to 11 °C. Xylem sap osmotic potential decreased from autumn to winter, reaching a minimum in March, and then increasing again. Soluble sugar (SS) concentration increased throughout the winter, peaked in March, and then decreased. Conclusions: These results suggest that (1) there is a hydraulic segmentation between the stem and leaf, which could prevent stem water loss and further embolization in winter; (2) maintenance of root pressure in early winter played an important role in reducing the effect of freeze-thaw cycles on the winter embolism; (3) the physiological process that resulted in a decrease in xylem sap osmotic potential and tissue water content, and an accumulation of SS associated with cold acclimation also aided in reducing the extent of freeze-thaw-induced embolism. All these strategies could be helpful for the maintenance of xylem hydraulic function of this bamboo species during winter.

Interactive effect between tree ageing and trunk-boring pest reduces hydraulics and carbon metabolism in Hippophae rhamnoides.

Sea-buckthorn (Hippophae rhamnoides) is widely distributed across the Eurasian continent. Recently sea-buckthorn has shown premature ageing and decline when confronted with water deficiency and Holcocerus hippophaecolus damage in northwest China and the Loess Plateau region. However, the physiological process of sea-buckthorn senescence in response to drought and pest damage is still unknown. In this study, 4-year-old (4y), 15-year-old normal growth (15yN) and 15-year-old seriously moth-damaged sea-buckthorn plants (15yH) were used as the research objects. The growth of branches and roots, branch water potential and percentage loss of conductivity (PLC), branch vulnerability to embolism (quantified by P50, xylem water potential at 50 % of PLC), branch xylem parenchyma cell viability, photosynthesis and the non-structural carbohydrate (NSC) content in branches and roots in dry and wet seasons were measured. The results showed that the length, basal diameter of 1-year-old branches and the leaf area of 4y trees were significantly larger than that of 15yN and 15yH trees, and the fine root density of 15yH trees was significantly lower than that of 15yN trees in all measured areas. The branch-specific hydraulic conductivity of 15yN and 15yH trees was only 50.2 % and 12.3 % of that of 4y trees, and the P50 of 4y, 15yH and 15yN trees was -3.69 MPa, -2.71 MPa and -1.15 MPa, respectively. The midday water potential and photosynthetic rate were highest in 4y trees, followed by 15yN and then 15yH trees in both the dry season and wet seasons, while branch PLC declined in the opposite direction (15yH trees highest, 4y trees lowest). The degree of PLC repair within a day was highest in 4y trees, followed by 15yN and then 15yH trees, and the viability of xylem cells was consistent with this pattern. The branch xylem starch and NSC content of 4y and 15yN trees were significantly higher than that of 15yH trees in the dry season, and the root starch and NSC content of 4y trees were significantly higher than that of 15yH trees in the two seasons. The above results suggest that the hydraulic properties of the normal elderly and seriously pest-damaged sea-buckthorn were significantly worse than in juvenile plants. Narrower early wood width and vessel density, high embolism vulnerability and weak embolism repair capacity led to the decline in water-conducting ability, and similarly further affected photosynthesis and the root NSC content. The decline in xylem parenchyma cell viability was the main reason for the limited embolism repair in the branches.

17ß-oestradiol alleviates endoplasmic reticulum stress injury induced by chronic cerebral hypoperfusion through the Haemoglobin/HIF 1α signalling pathway in ovariectomized rats.

Endoplasmic reticulum stress (ERS) is known to be an essential target in protecting against ischaemic brain injury. In this study, using a vascular dementia (VaD) animal model induced by bilateral common carotid artery occlusion (BCCAO), we evaluated the effect and mechanism of 17ß-oestradiol (E2) against VaD by inhibiting ERS at the early stage (14 d, 21 d, 28 d) and late stage (3 m) after BCCAO in the hippocampal CA1 region of ovariectomized rats. The results showed that the activation of the PERK-eIF2α-ATF4-CHOP axis, a typical ERS pathway, was significantly increased at the early and late stages after BCCAO. JNK (c-Jun N-terminal kinase)-cJun, a pro-death pathway, also displayed the same pattern as the ERS axis. E2 treatment profoundly suppressed the impairments caused by BCCAO. Further mechanistic studies revealed that cerebral blood flow (CBF) was sharply decreased at 14 d and returned to the normal level at 21 d after BCCAO. E2 could not change CBF, while it unexpectedly enhanced the ability to carry oxygen. This is evidenced by the fact that the protein expression of haemoglobin α/ß (Hα/ß), an oxygen carrier, robustly increased at BCCAO 21 d and 3 m after E2 treatment. The oxygen carrier increased strongly after 21 d and 3 m of BCCAO treated with E2. Moreover, E2 correspondingly enhanced the protein expression of hypoxia-inducible factor 1α (HIF 1α) in both the early and late stage after BCCAO in the hippocampal CA1 region. Finally, E2 administration markedly decreased the activities of caspase-8, caspase-3, and caspase-12 and increased the number of NeuN-positive cells. These findings suggest that E2 serves as a neuroprotectant to alleviate VaD by suppressing ERS injury involving the haemoglobin/HIF 1α signalling pathway.

Frost fatigue and its spring recovery of xylem conduits in ring-porous, diffuse-porous, and coniferous species in situ.

Frost-induced embolism and frost fatigue are two major aspects of frost damage to xylem water transport in trees. In this study, three species of each ring-porous, diffuse-porous, and coniferous trees growing in situ were used to explore their differences in winter embolism and frost fatigue. Changes in predawn water potential, predawn native embolism, maximal specific conductivity (Kmax), and cavitation resistance (P50, xylem water potential at 50% loss of conductivity) of current-year branches were measured from autumn to spring. Maximum native embolism of late winter was near 100% for ring-porous species, approximately 80% for diffuse-porous species, and below 50% for conifers. In early spring, there was no significant reduction of native embolism until formation of new vessels in ring-porous trees, while diffuse-porous trees and conifers exhibited a reduction in native embolism before development of new xylem. There was a significant decrease in P50 of ring- and diffuse-porous species over winter; however, in May P50 was markedly reduced along with formation of new vessels. Kmax of ring- and diffuse-porous species significantly decreased from autumn to late winter. The results revealed that vulnerability to cavitation and frost fatigue was related to conduit diameter. The strategies for coping with winter embolism differed among the three wood types: in ring-porous species there was no active embolism refilling; in diffuse-porous species there was refilling associated with positive xylem pressure; and in conifers there was refilling without positive xylem pressure. New vessels could completely restore stem hydraulic conductivity but only partially restore xylem cavitation resistance in spring.

Relative contributions of hydraulic dysfunction and carbohydrate depletion during tree mortality caused by drought.

Drought-induced tree mortality has been observed worldwide. Nevertheless, the physiological mechanisms underlying this phenomenon are still being debated. Potted Robinia pseudoacacia and Platycladus orientalis saplings were subjected to drought and their hydraulic failure and carbon starvation responses were studied. They underwent simulated fast drought (FD) and slow drought (SD) until death. The dynamics of their growth, photosynthesis, water relations and carbohydrate concentration were measured. The results showed that during drought, growth and photosynthesis of all saplings were significantly reduced in both species. The predawn water potential in both species was ~ -8 MPa at mortality. The percentage loss of conductivity (PLC) was at a maximum at mortality under both FD and SD. For R. pseudoacacia and P. orientalis, they were >95 and ~45 %, respectively. At complete defoliation, the PLC of R. pseudoacacia was ~90 % but the trees continued to survive for around 46 days. The non-structural carbohydrate (NSC) concentrations in the stems and roots of both FD and SD R. pseudoacacia declined to a very low level near death. In contrast, the NSC concentrations in the needles, stems and roots of P. orientalis at mortality under FD did not significantly differ from those of the control, whereas the NSC concentrations in SD P. orientalis stems and roots at death were significantly lower than those of the control. These results suggest that the duration of the drought affected NSC at mortality in P. orientalis. In addition, the differences in NSC between FD and SD P. orientalis did not alter mortality thresholds associated with hydraulic failure. The drought-induced death of R. pseudoacacia occurred at 95 % PLC for both FD and SD, indicating that hydraulic failure played an important role in mortality. Nevertheless, the consistent decline in NSC in R. pseudoacacia saplings following drought-induced defoliation may have also contributed to its mortality.

Phenology-dependent variation in the non-structural carbohydrates of broadleaf evergreen species plays an important role in determining tolerance to defoliation (or herbivory).

Two broadleaf evergreen canopy species (Schima superba and Engelhardia roxburghiana) with different phenologies in a subtropical region of southern China were used to determine the influence of leaf phenology on the impact of an insect pest attack. S. superba regenerates its leaves in February, while E. roxburghiana regenerates its leaves in May. The moth Thalassodes quadraria attacked the two broadleaf evergreen species in March to April, and the newly produced leaves were removed for S. superba but not for E. roxburghiana. The young trees were artificially defoliated to imitate an insect pest attack during March 2014. Nonstructural carbohydrate (NSC) and growth measurements and a retrospective analysis based on the radial growth of mature trees were conducted in January 2015. The results showed that NSC concentrations decreased in S. superba during canopy rebuilding, and the subsequent defoliation severely inhibited leaf and shoot growth, prevented NSC restoration in roots and stem xylem, and caused high mortality. The insect outbreaks reduced the radial growth of S. superba. In contrast, E. roxburghiana experienced less growth retardation, lower mortality, and normal radial growth. Thus, taking phenology-dependent variation in NSCs into consideration, defoliation and insect pest outbreaks more negatively impacted S. superba than E. roxburghiana.

Protective Effect of 17ß-Estradiol Upon Hippocampal Spine Density and Cognitive Function in an Animal Model of Vascular Dementia.

The current study examined whether the steroid hormone, 17ß-estradiol (E2) can exert long-lasting beneficial effects upon axonal health, synaptic plasticity, dementia-related amyloid-beta (Aß) protein expression, and hippocampal-dependent cognitive function in an animal model of chronic cerebral hypoperfusion and vascular dementia (VaD). Chronic cerebral hypoperfusion and VaD was induced by bilateral common carotid artery occlusion (BCCAO) in adult male Sprague Dawley rats. Low dose E2 administered for the first 3-months after BCCAO exerted long-lasting beneficial effects, including significant neuroprotection of hippocampal CA1 neurons and preservation of hippocampal-dependent cognitive function when examined at 6-months after BCCAO. E2 treatment also prevented BCCAO-induced damage to hippocampal myelin sheaths and oligodendrocytes, enhanced expression of the synaptic proteins synaptophysin and PSD95 in the hippocampus, and prevented BCCAO-induced loss of total and mushroom dendritic spines in the hippocampal CA1 region. Furthermore, E2-treatment also reduced BCCAO induction of dementia-related proteins expression such as p-tau (PHF1), total ubiquitin, and Aß1-42, when examined at 6 m after BCCAO. Taken as a whole, the results suggest that low-dose E2 replacement might be a potentially promising therapeutic modality to attenuate or block negative neurological consequences of chronic cerebral hypoperfusion and VaD.