Physiological and growth responses of eleven Ontario provenances of one-year old Picea glauca seedlings to elevated CO2 concentrations

To study the physiological and growth responses of eleven Ontario provenances of white spruce [Picea glauca (Moench) Voss] to elevated atmospheric CO2 concentrations, one-year old seedlings were grown in three greenhouses under CO2 concentrations of ambient, 530 ppm, and 700 ppm for a period 90 days. The following physiological traits were measured after 60 and 90 days of treatment: net assimilation rate (A), stomatal conductance (gs), transpiration (E), water-use efficiency (WUE), and intercellular to ambient CO2 concentration ratio (C|/Ca). Shoot, root, and total biomass and biomass allocation were also measured after 60 and 90 days of treatment. Height and root collar diameter (RCD) data were collected after 0, 30, 60, and 90 days of treatment. Net CO2 assimilation was significantly enhanced by elevated [CO2 ] after 60 and 90 days of treatment despite reductions in photosynthetic capacity. Elevated [CO2 ] also enhanced WUE and decreased gs and E after 60 days of treatment. There was significant down-regulation of photosynthesis in response to CO2 concentration elevation. Elevated [CO2] significantly reduced Rubisco carboxylation efficiency (Vcmax), RuBP regeneration capacity (Jmax), and triose phosphate utilisation (TPU), but had no significant effect on leaf respiration (Rj) or C 0 2 compensation point. Despite its substantial influence on gas exchange, CO2 concentration did not significantly affect seedling biomass, biomass allocation, height, or RCD. No significant CO2 x provenance interactions were found in the gas exchange measurements. Provenance had a significant effect on the height and RCD of the white spruce seedlings. Strong correlations existed between gas exchange and monthly climate variables for the 11 Ontario provenances of white spruce at ambient and elevated CO2 concentrations, suggesting adaptation of individual provenances to local climate. The implications of CO2 response of diverse sources of white spruce seedlings on tree improvement programs will probably be minimal. Seed sources of white spruce in Ontario selected for superior growth characteristics in the present climate will probably perform well in the predicted future climate

Cochlin Induced TREK-1 Co-Expression and Annexin A2 Secretion: Role in Trabecular Meshwork Cell Elongation and Motility

Fluid flow through large interstitial spaces is sensed at the cellular level, and mechanistic responses to flow changes enables expansion or contraction of the cells modulating the surrounding area and brings about changes in fluid flow. In the anterior eye chamber, aqueous humor, a clear fluid, flows through trabecular meshwork (TM), a filter like region. Cochlin, a secreted protein in the extracellular matrix, was identified in the TM of glaucomatous patients but not controls by mass spectrometry. Cochlin undergoes shear induced multimerization and plays a role in mechanosensing of fluid shear. Cytoskeletal changes in response to mechanosensing in the ECM by cochlin will necessitate transduction of mechanosensing. TREK-1, a stretch activated outward rectifying potassium channel protein known to act as mechanotransducer was found to be expressed in TM. Cochlin expression results in co-expression of TREK-1 and filopodia formation. Prolonged cochlin expression results in expression and subsequent secretion of annexin A2, a protein known to play a role in cytoskeletal remodeling. Cochlin interacts with TREK-1 and annexin A2. Cochlin-TREK-1 interaction has functional consequences and results in changes in cell shape and motility. Annexin A2 expression and secretion follows cochlin-TREK-1 syn-expression and correlates with cell elongation. Thus cytoskeleton changes in response to fluid shear sensed by cochlin are further mediated by TREK-1 and annexin A2

Cochlin, Intraocular Pressure Regulation and Mechanosensing

Fluid shear modulates many biological properties. How shear mechanosensing occurs in the extracellular matrix (ECM) and is transduced into cytoskeletal change remains unknown. Cochlin is an ECM protein of unknown function. Our investigation using a comprehensive spectrum of cutting-edge techniques has resulted in following major findings: (1) over-expression and down-regulation of cochlin increase and decrease intraocular pressure (IOP), respectively. The overexpression was achieved in DBA/2J-Gpnmb+/SjJ using lentiviral vectors, down-regulation was achieved in glaucomatous DBA/2J mice using targeted disruption (cochlin-null mice) and also using lentiviral vector mediated shRNA against cochlin coding region; (2) reintroduction of cochlin in cochlin-null mice increases IOP; (3) injection of exogenous cochlin also increased IOP; (4) increasing perfusion rates increased cochlin multimerization, which reduced the rate of cochlin proteolysis by trypsin and proteinase K; The cochlin multimerization in response to shear stress suggests its potential mechanosensing. Taken together with previous studies, we show cochlin is involved in regulation of intraocular pressure in DBA/2J potentially through mechanosensing of the shear stress

Aqueous outflow: Segmental and distal flow

A prominent risk factor of primary open-angle glaucoma is ocular hypertension, a pathologic state caused by impaired outflow of aqueous humor through the trabecular meshwork within the iridocorneal angle. The juxtacanalicular region of the trabecular meshwork and the inner wall of Schlemm canal have been identified as the main contributors to aqueous outflow resistance, and both extracellular matrix within the trabecular meshwork and trabecular meshwork cell shape have been shown to affect outflow. Overexpression of multiple ECM proteins in perfused cadaveric human eyes has led to increased outflow resistance and elevated IOP. Pharmacologic agents targeting trabecular meshwork cytoskeletal arrangements have been developed after multiple studies demonstrated the importance of cell shape on outflow. Several groups have shown that aqueous outflow occurs only at certain segments of the trabecular meshwork circumferentially, a concept known as segmental flow. This is based on the theory that aqueous outflow is dependent on the presence of discrete pores within the Schlemm canal. Segmental flow has been described in the eyes of multiple species, including primate, bovine, mouse, and human samples. While the trabecular meshwork appears to be the major source of resistance, trabecular meshwork bypass procedures have been unable to achieve the degree of IOP reduction observed with trabeculectomy, reflecting the potential impact of distal flow, or flow through Schlemm canal and collector channels, on outflow. Multiple studies have demonstrated that outflow occurs preferentially near collector channels, suggesting that these distal structures may be more important to aqueous outflow than previously believed