Aperture In Response Research Articles

Possible involvement of phospholipase A2 in light signal transduction of guard cells of Commelina communis

Polyunsaturated fatty acids induce stomatal opening (Y. Lee, H. Lee, R. C. Crain, A. Lee and S. J. Korn. 1994. Cell Signal. 6: 181–186), but it is not known whether they function as second messengers in guard cells exposed to signals that open stomata. To test the hypothesis that phospholipase A2 (PLA2), which produces fatty acids and lysophospholipids, is involved in light signal transduction in guard cells, we treated epidermal peels of Commelina communis L. with PLA2 inhibitors and followed the changes in stomatal apertures in response to light. Stomatal opening by white, blue, or red light was inhibited by 2–3 different PLA2 inhibitors in concentration ranges that have been reported to inhibit PLA2 activity. However, the PLA2 inhibitors could not block stomatal opening induced by a polyunsaturated fatty acid. These results suggest that PLA2 functions as a signal transducer for both blue and red light in guard cells.

Eyelid Movement During Complete Neuromuscular Block

Eyelid Movement During Complete Neuromuscular Block

Co-ordination of signalling elements in guard cell ion channel control

Fine regulation of solutes transport across the guard cell plasma membrane for osmotic modulation is essential for the maintenance of the proper stomatal aperture in response to environmental stimuli. The major osmotica, K + , Cl - and malate are transported through selective ion channels in the plasma membrane and tonoplast of guard cells. To date, a number of ion channels have been shown to operate in the guard cell plasma membrane: outwardly- and inwardly-rectifying K + channels (I K,in and I K,out ), slowly- and rapid-activating anion channels, and stretch-activated non-selective channels. Slow and fast vacuolar channels (SV and FV) and voltage-independent K + -selective (VK) channels have been found at the guard cell tonoplast. On the molecular level, the regulation of the stomatal aperture is achieved by precise spatial and temporal co-ordination of channel activities through a network of signalling cascades that can be triggered, among others, by plant hormones. ABA and auxin as regulators of stomatal aperture have received most attention to date. It is clear now that the effect of these hormones on ion channels is mediated by second messengers pH i and [Ca 2+ ] i . The effect of ABA is generally associated with increases in pH i , while auxin acidifies the cytosol. Both of these hormones may induce elevation in [Ca 2+ ] i . Phosphorylation is another important factor in cellular signalling. The ABI1 gene encoding a 2C-type protein phosphatase has been shown to be a key element of ABA-dependent cascades. Plasma membrane voltage is also an important component of signalling and channel control, and has recently been shown to influence cytosolic-free [Ca 2+ ]. Thus, transduction of these, and associated cytoplasmic signals is clearly non-linear, and is probably important for providing a plasticity of cellular response to external and environmental stimuli. Understanding the interdependence and hierarchy of signalling elements now presents a major challenge for research in plant biology.

Two plasma membrane H(+)-ATPase genes expressed in guard cells of Vicia faba are also expressed throughout the plant.

Guard cells modulate stomatal apertures in response to hormones, metabolic demands and environmental stimuli. The guard cell PM H(+)-ATPases play a critical role in this process by generating the electrochemical gradient to drive solute transport and concomitant water flux. The PM H(+)-ATPase activity is specifically regulated by red and blue light, fungal toxins and auxin. To determine if the unique responsiveness of the guard cell PM H(+)-ATPase is due to the expression of a cell-specific isoform, we amplified by PCR, and cloned portions of PM H(+)-ATPase genes VHA1 and VHA2, which are expressed in guard cell protoplasts (GCP). In situ hybridization to leaf tissue sections indicated that VHA1 and VHA2 genes were expressed in guard cells and mesophyll cells but not in epidermal cells or vascular tissues. Furthermore, a gene-specific quantitative reverse transcription (RT)-PCR detected VHA1 and VHA2 mRNAs in both GCP and mesophyll cell protoplast mRNA as well as in mRNA isolated from roots, leaves, stems and flowers. Thus, two PM H(+)-ATPase genes expressed in guard cells are also expressed in many other tissues and cell types. This suggests that the unique responsiveness of the guard cell PM H(+)-ATPases to environmental stimuli results from cell-specific signal transduction pathways rather than the expression of a cell-specific PM H(+)-ATPase.

Leaf and canopy responses to elevated CO2 in a pine forest under free-air CO2 enrichment.

Physiological responses to elevated CO2 at the leaf and canopy-level were studied in an intact pine (Pinus taeda) forest ecosystem exposed to elevated CO2 using a free-air CO2 enrichment (FACE) technique. Normalized canopy water-use of trees exposed to elevated CO2 over an 8-day exposure period was similar to that of trees exposed to current ambient CO2 under sunny conditions. During a portion of the exposure period when sky conditions were cloudy, CO2-exposed trees showed minor (≤7%) but significant reductions in relative sap flux density compared to trees under ambient CO2 conditions. Short-term (minutes) direct stomatal responses to elevated CO2 were also relatively weak (≈5% reduction in stomatal aperture in response to high CO2 concentrations). We observed no evidence of adjustment in stomatal conductance in foliage grown under elevated CO2 for nearly 80 days compared to foliage grown under current ambient CO2, so intrinsic leaf water-use efficiency at elevated CO2 was enhanced primarily by direct responses of photosynthesis to CO2. We did not detect statistical differences in parameters from photosynthetic responses to intercellular CO2 (A net-C i curves) for Pinus taeda foliage grown under elevated CO2 (550 μmol mol-1) for 50-80 days compared to those for foliage grown under current ambient CO2 from similar-sized reference trees nearby. In both cases, leaf net photosynthetic rate at 550 μmol mol-1 CO2 was enhanced by approximately 65% compared to the rate at ambient CO2 (350 μmol mol-1). A similar level of enhancement under elevated CO2 was observed for daily photosynthesis under field conditions on a sunny day. While enhancement of photosynthesis by elevated CO2 during the study period appears to be primarily attributable to direct photosynthetic responses to CO2 in the pine forest, longer-term CO2 responses and feedbacks remain to be evaluated.

Expiratory pattern and laryngeal responses to single-breath expiratory resistance loads

Responses of expiratory duration (T E) and laryngeal aperture to small flow resistance loads (2 and 5 cm H 2O/LPS) applied to single expirations were measured using repeated applications in four subjects during quiet breathing. All subjects significantly prolonged T E in response to the higher load and 3 of the 4 showed that same response to the lower load, which was not perceived by these subjects. These same 3 subjects showed a narrowed laryngeal aperture in response to loading such that their expiratory impedance must have been greater than the increase provided by the load alone. The effect of such a loading response was to slow the expiratory volume decay so that a small but significantly increase in the halftime for volume decay was observed. The prolongation of T E seen with loading could be due to the alteration of volume-related feedback consequent to the increased expiratory impedance. This may serve a role in regulation of expiratory muscle function.