Concerted Action of Evolutionarily Ancient and Novel SNARE Complexes in Flowering-Plant Cytokinesis

Membrane vesicles delivered to the cell-division plane fuse with one another to form the partitioning membrane during plant cytokinesis, starting in the cell center. In Arabidopsis, this requires SNARE complexes involving the cytokinesis-specific Qa-SNARE KNOLLE. However, cytokinesis still occurs in knolle mutant embryos, suggesting contributions from KNOLLE-independent SNARE complexes. Here we show that Qa-SNARE SYP132, having counterparts in lower plants, functionally overlaps with the flowering plant-specific KNOLLE. SYP132 mutation causes cytokinesis defects, knolle syp132 double mutants consist of only one or a few multi-nucleate cells, and SYP132 has the same SNARE partners as KNOLLE. SYP132 and KNOLLE also have non-overlapping functions in secretion and in cellularization of the embryo-nourishing endosperm resulting from double fertilization unique to flowering plants. Evolutionarily ancient non-specialized SNARE complexes originating in algae were thus amended by the appearance of cytokinesis-specific SNARE complexes, meeting the high demand for membrane-fusion capacity during endosperm cellularization in angiosperms. In plant cytokinesis, SNARE complexes mediate vesicle fusion for partitioning membrane formation. Park et al. show that evolutionarily ancient Qa-SNARE SYP132 functionally overlaps with flowering plant- and cytokinesis-specific Qa-SNARE KNOLLE. KNOLLE acquisition may have been due to high demand for membrane-fusion capacity during endosperm cellularization in flowering plants

Neurohumoral and metabolic response to exercise in water.

Item does not contain fulltextAtrial natriuretic peptide (ANP) stimulates lipid mobilization and lipid oxidation in humans. The mechanism appears to promote lipid mobilization during exercise. We tested the hypothesis that water immersion augments exercise-induced ANP release and that the change in ANP availability is associated with increased lipid mobilization and lipid oxidation. In an open randomized and cross-over fashion we studied 17 men (age 31+/-3.6 years; body mass index 24+/-1.7 kg/m(2); body fat 17+/-6.7%) on no medication. Subjects underwent two incremental exercise tests on a bicycle ergometer. One test was conducted on land and the other test during immersion in water up to the xiphoid process. In a subset (n=7), we obtained electromyography recordings in the left leg. We monitored gas exchange, blood pressure, and heart rate. In addition, we obtained blood samples towards the end of each exercise step to determine ANP, norepinephrine, epinephrine, lactate, free fatty acids, insulin, and glucose concentrations. Heart rate, systolic blood pressure, and oxygen consumption at the anaerobic threshold and during peak exercise were similar on land and with exercise in water. The respiratory quotient was mildly reduced when subjects exercised in water. Glucose and lactate measurements were decreased whereas free fatty acid concentrations were increased with exercise in water. Water immersion attenuated epinephrine and norepinephrine and augmented ANP release during exercise. Even though water immersion blunts exercise-induced sympathoadrenal activation, lipid mobilization and lipid oxidation rate are maintained or even improved. The response may be explained by augmented ANP release.1 mei 201