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Objective. C4-derived activation fragments are the only complement ligands present on the surfaces of normal erythrocytes. The significance of this observation is unknown, and the role of erythrocyte-bound C4 (E-C4) in human disease has not been explored. More than any other human disease, the pathogenesis of systemic lupus erythematosus (SLE) has been characterized by defects in clearance of complement-bearing immune complexes via erythrocytes expressing complement receptor 1 (CR1). This study was undertaken to determine whether these functional defects might be reflected by abnormal patterns of E-C4 and E-CR1 expression on erythrocytes of patients with SLE.Methods. We conducted a cross-sectional study of 100 patients with SLE, 133 patients with other diseases, and 84 healthy controls. Erythrocytes were characterized by indirect immunofluorescence and by flow cytometry for determination of levels of C4d and CR1.Results. Patients with SLE had higher levels of E-C4d and lower levels of E-CR1 than did patients with other diseases (P < 0.001) or healthy controls (P < 0.001). The test was 81% sensitive and 91% specific for SLE versus healthy controls and 72% sensitive and 79% specific for SLE versus other diseases, and it had an overall negative predictive value of 92%.Conclusion. This is the first report of abnormal levels of E-C4d in human disease. We found that abnormally high levels of E-C4d and low levels of E-CR1 are characteristic of SLE, and combined measurement of the 2 molecules has high diagnostic sensitivity and specificity for lupus. Determination of E-C4d/E-CR1 levels may be a useful addition to current tests and criteria for SLE diagnosis.It has been known for decades that proteolytic fragments of complement component C4, generated during activation of the classical pathway, are present on surfaces of normal erythrocytes. C4 is a class III HLA molecule, and its polymorphism is responsible for the Rogers and Chido blood group antigens; however, the physiologic significance of erythrocyte-bound C4 (E-C4) is entirely unknown. Although there has been extensive study of serum C4 levels in human disease, abnormalities of E-C4 and the potential role of E-C4 molecules during inflammatory and immune responses have not been investigated.A large body of evidence accumulated over several decades has demonstrated that abnormalities in complement activation and clearance of immune complexes by erythrocytes are fundamental to the pathogenesis of systemic lupus erythematosus (SLE) (1,2). These include reduced levels of CR1 on erythrocytes, deficiencies in components of the classical pathway including C4, and saturation of CR1 by preexisting immune complexes (3-12). These observations led to our hypothesis that abnormalities in complement activation specific to SLE may be reflected by molecular events involving both receptors and ligands on erythrocyte surfaces and that

Land plants must balance CO 2 assimilation with transpiration in order to minimize drought stress and maximize their reproductive success. The ratio of assimilation to transpiration is called transpiration efficiency (TE). TE is under genetic control, although only one specific gene, ERECTA, has been shown to regulate TE. We have found that the a-subunit of the heterotrimeric G protein in Arabidopsis (Arabidopsis thaliana), GPA1, is a regulator of TE. gpa1 mutants, despite having guard cells that are hyposensitive to abscisic acid-induced inhibition of stomatal opening, have increased TE under ample water and drought stress conditions and when treated with exogenous abscisic acid. Leaf-level gas-exchange analysis shows that gpa1 mutants have wild-type assimilation versus internal CO 2 concentration responses but exhibit reduced stomatal conductance compared with ecotype Columbia at ambient and below-ambient internal CO 2 concentrations. The increased TE and reduced whole leaf stomatal conductance of gpa1 can be primarily attributed to stomatal density, which is reduced in gpa1 mutants. GPA1 regulates stomatal density via the control of epidermal cell size and stomata formation. GPA1 promoter::b-glucuronidase lines indicate that the GPA1 promoter is active in the stomatal cell lineage, further supporting a function for GPA1 in stomatal development in true leaves.Land plants, in particular plants that utilize C 3 photosynthesis, must balance CO 2 acquisition with water loss in order to maximize fitness. The water loss cost per unit of biomass acquired can be expressed as transpiration efficiency (TE; also referred to as wateruse efficiency), the ratio of CO 2 assimilation (A) to transpiration. TE strongly correlates with the d 13 C of plant tissue, the ratio of 13 C to 12

Summary Phenotypic plasticity is the ability of one genotype to display different phenotypes under different environmental conditions. Although variation for phenotypic plasticity has been documented in numerous species, little is known about the genetic mechanisms underlying phenotypic plasticity. Given their widespread roles in hormonal and environmental signaling, we examined whether genes which encode heterotrimeric G proteins are plasticity genes. We grew multiple alleles of heterotrimeric G‐protein mutants, together with wild‐type Arabidopsis thaliana, under different watering regimes to determine the contributions of G‐protein genes to phenotypic plasticity for a number of developmental and reproduction‐related traits. G‐protein mutations did not affect significantly the amount of phenotypic variation within an environment for any trait, but did affect significantly the amount of phenotypic plasticity for certain traits. AGB1, which encodes the β subunit of the heterotrimeric G protein in Arabidopsis, is a plasticity gene and regulates reproductive trait plasticity in response to water availability, resulting in increased fitness (defined as seed production) under drought stress.

INTRODUCTIONThe flux of ions across membranes via ion channels is vital to cellular responses to internal and external stimuli, and therefore to cellular survival in changing circumstances. Patch clamping is a powerful technique for ion channel investigation, because it enables measurement of both net ion fluxes across the entire surface area of a cell and ion currents flowing through a single open channel. However, unlike animal cells, plant cells are surrounded by cell walls that prevent the physical contact between the patch pipette and the plasma membrane necessary for the patch clamp technique. To demonstrate how patch clamping can be applied to plant physiology research, we describe a protocol used to record potassium ion (K(+)) channel currents in Arabidopsis guard cell protoplasts (a widely studied model cell type in plant biology). The protocol requires a two-step cellulase and pectinase digestion to isolate high quality Arabidopsis guard cell protoplasts (i.e., plant cells lacking their cell walls), preparation of suitable glass capillary microelectrodes, and formation of the whole-cell configuration with a gigaohm (GΩ) seal. We also describe the history of the protocol and list other types of plant cells from which successful patch clamp recordings have been obtained.