Outside-Xylem Vulnerability, Not Xylem Embolism, Controls Leaf Hydraulic Decline during Dehydration.

Leaf hydraulic supply is crucial to maintaining open stomata for CO2 capture and plant growth. During drought-induced dehydration, the leaf hydraulic conductance (Kleaf) declines, which contributes to stomatal closure and, eventually, to leaf death. Previous studies have tended to attribute the decline of Kleaf to embolism in the leaf vein xylem. We visualized at high resolution and quantified experimentally the hydraulic vulnerability of xylem and outside-xylem pathways and modeled their respective influences on plant water transport. Evidence from all approaches indicated that the decline of Kleaf during dehydration arose first and foremost due to the vulnerability of outside-xylem tissues. In vivo x-ray microcomputed tomography of dehydrating leaves of four diverse angiosperm species showed that, at the turgor loss point, only small fractions of leaf vein xylem conduits were embolized, and substantial xylem embolism arose only under severe dehydration. Experiments on an expanded set of eight angiosperm species showed that outside-xylem hydraulic vulnerability explained 75% to 100% of Kleaf decline across the range of dehydration from mild water stress to beyond turgor loss point. Spatially explicit modeling of leaf water transport pointed to a role for reduced membrane conductivity consistent with published data for cells and tissues. Plant-scale modeling suggested that outside-xylem hydraulic vulnerability can protect the xylem from tensions that would induce embolism and disruption of water transport under mild to moderate soil and atmospheric droughts. These findings pinpoint outside-xylem tissues as a central locus for the control of leaf and plant water transport during progressive drought.

Leaf vein xylem conduit diameter influences susceptibility to embolism and hydraulic decline.

Ecosystems worldwide are facing increasingly severe and prolonged droughts during which hydraulic failure from drought-induced embolism can lead to organ or whole plant death. Understanding the determinants of xylem failure across species is especially critical in leaves, the engines of plant growth. If the vulnerability segmentation hypothesis holds within leaves, higher order veins that are most terminal in the plant hydraulic system should be more susceptible to embolism to protect the rest of the water transport system. Increased vulnerability in the higher order veins would also be consistent with these experiencing the greatest tensions in the plant xylem network. To test this hypothesis, we combined X-ray micro-computed tomography imaging, hydraulic experiments, cross-sectional anatomy and 3D physiological modelling to investigate how embolisms spread throughout petioles and vein orders during leaf dehydration in relation to conduit dimensions. Decline of leaf xylem hydraulic conductance (Kx ) during dehydration was driven by embolism initiating in petioles and midribs across all species, and Kx vulnerability was strongly correlated with petiole and midrib conduit dimensions. Our simulations showed no significant impact of conduit collapse on Kx decline. We found xylem conduit dimensions play a major role in determining the susceptibility of the leaf water transport system during strong leaf dehydration.

The impact of tocilizumab on physical function and quality of life in patients with rheumatoid arthritis: a systematic literature review and interpretation.

OBJECTIVE: To determine the impact of tocilizumab on physical function and quality of life in patients diagnosed with rheumatoid arthritis. METHODS: A systematic literature review was performed to select for trials that could be used to examine the impact of tocilizumab on patients in terms of health-related physical function, quality of life, and quality of sleep. By examining background therapy, disease duration, and remission rates, we were able to determine the impact that a dose of tocilizumab has on various patients. RESULTS: A total of 2617 tocilizumab-treated patients and 1271 controls were available for this study. Tocilizumab improved the Health Assessment Questionnaire Disability Index score statistically in comparison to the controls, with odds ratios from 1.4 to 7.0. Tocilizumab improved the physical function measure substantially more than the minimal clinically important difference (MCID) (5 units) - 8.9 and 9.7 - compared to 4.1 and 5.0 for controls. Seven and nine units of improvement were observed when measuring fatigue in rheumatoid arthritis patients. Using the Epworth Sleepiness Scale, we found that sleep improved (from 7.7 [3.1] to 3.4 [2.2]). CONCLUSION: Tocilizumab improves function and quality of life and decreases fatigue in patients with rheumatoid arthritis.