Water-stress physiology of Rhinanthus alectorolophus, a root-hemiparasitic plant.

Root-hemiparasitic plants of the genus Rhinanthus acquire resources through a water-wasting physiological strategy based on high transpiration rate mediated by the accumulation of osmotically active compounds and constantly open stomata. Interestingly, they were also documented to withstand moderate water stress which agrees with their common occurrence in rather dry habitats. Here, we focused on the water-stress physiology of Rhinanthus alectorolophus by examining gas exchange, water relations, stomatal density, and biomass production and its stable isotope composition in adult plants grown on wheat under contrasting (optimal and drought-inducing) water treatments. We also tested the effect of water stress on the survival of Rhinanthus seedlings, which were watered either once (after wheat sowing), twice (after wheat sowing and the hemiparasite planting) or continuously (twice and every sixth day after that). Water shortage significantly reduced seedling survival as well as the biomass production and gas exchange of adult hemiparasites. In spite of that drought-stressed and even wilted plants from both treatments still considerably photosynthesized and transpired. Strikingly, low-irrigated plants exhibited significantly elevated photosynthetic rate compared with high-irrigated plants of the same water status. This might relate to biochemical adjustments of these plants enhancing the resource uptake from the host. Moreover, low-irrigated plants did not acclimatize to water stress by lowering their osmotic potential, perhaps due to the capability to tolerate drought without such an adjustment, as their osmotic potential at full turgor was already low. Contrary to results of previous studies, hemiparasites seem to close their stomata in response to severe drought stress and this happens probably passively after turgor is lost in guard cells. The physiological traits of hemiparasites, namely the low osmotic potential associated with their parasitic lifestyle and the ability to withstand drought and recover from the wilting likely enable them to grow in dry habitats. However, the absence of osmotic adjustment of adults and sensitivity of seedlings to severe drought stress demonstrated here may result in a substantial decline of the hemiparasitic species with ongoing climate change.

Hydathode trichomes actively secreting water from leaves play a key role in the physiology and evolution of root-parasitic rhinanthoid Orobanchaceae.

BACKGROUND AND AIMS: Root hemiparasites from the rhinanthoid clade of Orobanchaceae possess metabolically active glandular trichomes that have been suggested to function as hydathode trichomes actively secreting water, a process that may facilitate resource acquisition from the host plant's root xylem. However, no direct evidence relating the trichomes to water secretion exists, and carbon budgets associated with this energy-demanding process have not been determined. METHODS: Macro- and microscopic observations of the leaves of hemiparasitic Rhinanthus alectorolophus were conducted and night-time gas exchange was measured. Correlations were examined among the intensity of guttation, respiration and transpiration, and analysis of these correlations allowed the carbon budget of the trichome activity to be quantified. We examined the intensity of guttation, respiration and transpiration, correlations among which indicate active water secretion. KEY RESULTS: Guttation was observed on the leaves of 50 % of the young, non-flowering plants that were examined, and microscopic observations revealed water secretion from the glandular trichomes present on the abaxial leaf side. Night-time rates of respiration and transpiration and the presence of guttation drops were positively correlated, which is a clear indicator of hydathode trichome activity. Subsequent physiological measurements on older, flowering plants indicated neither intense guttation nor the presence of correlations, which suggests that the peak activity of hydathodes is in the juvenile stage. CONCLUSIONS: This study provides the first unequivocal evidence for the physiological role of the hydathode trichomes in active water secretion in the rhinanthoid Orobanchaceae. Depending on the concentration of organic elements calculated to be in the host xylem sap, the direct effect of water secretion on carbon balance ranges from close to neutral to positive. However, it is likely to be positive in the xylem-only feeding holoparasites of the genus Lathraea, which is closely related to Rhinanthus. Thus, water secretion by the hydathodes might be viewed as a physiological pre-adaptation in the evolution of holoparasitism in the rhinanthoid lineage of Orobanchaceae.

Interleukin-6 gene variants and the risk of sepsis development in children.

A proinflammatory cytokine interleukin-6 (IL-6) plays an important role in the development, pathogenesis and outcome of SIRS, sepsis and septic shock. We have evaluated the role of the IL-6 gene polymorphisms in pediatric patients. A total of 421 consecutive pediatric patients admitted to the pediatric intensive care unit with fever, systemic inflammatory response syndrome (SIRS), sepsis, severe sepsis, septic shock, or multiple organ distress syndrome (MODS) were studied together with 644 healthy controls. DNA was isolated and two IL-6 gene polymorphisms (G-174>C and G-572>C) were analyzed. The frequencies of both analyzed variants differ significantly between the group of patients and healthy controls (p = 0.02 for G-174>C and p = 0.049 for G-572>C). In addition, genetic analysis of the G-174>C IL-6 gene variant revealed significant differences between the subgroup of febrile patients and subgroup of septic shock (p = 0.0319) and between the subgroup of SIRS and septic shock (p = 0.038). In both cases the negative genotype was CC. No statistically significant differences for the IL-6 gene polymorphism G-572>C were found between the groups of patients with different diagnosis. IL-6 gene polymorphisms G-174>C and G-572>C could be the predictors of risk of development and/or the predictors of the severity of sepsis in children.

Bactericidal permeability increasing protein gene variants in children with sepsis.

OBJECTIVE: To evaluate the role of genetic polymorphisms of the bactericidal permeability increasing protein (BPI) in pediatric patients with sepsis. DESIGN: Prospective, single-center, case-control study at the pediatric intensive care unit (PICU) of a university hospital. PATIENTS: 345 consecutive pediatric patients admitted to the PICU with fever, systemic inflammatory response syndrome (SIRS), sepsis, severe sepsis, septic shock, or multiple organ distress syndrome (MODS). INTERVENTIONS: DNA was isolated and two BPI gene polymorphisms BPI (G545 > C) Taq and BPI (A645[ > G) 216 were studied in patients and compared with healthy controls. MEASUREMENTS AND RESULTS: Genetic analysis of the BPI Taq gene revealed significant differences between healthy controls and the subgroup of febrile patients (p = 0.0243), the subgroup of SIRS and sepsis (p = 0.0101), and the subgroup of severe sepsis, septic shock, and MODS (p = 0.0027), respectively. No statistically significant differences for the BPI 216 gene polymorphism were found between patient and healthy control groups. A statistically significant predisposition to Gram-negative sepsis in patients carrying the BPI Taq GG variant together with the BPI 216 AG or GG variant was revealed (p = 0.0081), and these haplotypes were also associated with death due to sepsis-related complications. CONCLUSION: BPI Taq gene polymorphism is the accurate predictor of the severity of sepsis in children admitted to the PICU.