Homologue structure of the SLAC1 anion channel for closing stomata in leaves
Yu-hang ChenLei HuMarco PuntaRenato BruniB. HillerichBrian KlossBurkhard RostJ. LoveSteven A. SiegelbaumWayne A. Hendrickson
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Differential Responses of Abaxial and Adaxial Guard Cells of Broad Bean to Abscisic Acid and Calcium
Abstract Regulation by abscisic acid (ABA) and Ca2+ of broad bean (Vicia faba) abaxial and adaxial guard cell movements and inward K+ currents were compared. One millimolar Ca2+ in the bathing medium inhibited abaxial stomatal opening by 60% but only inhibited adaxial stomatal opening by 15%. The addition of 1 μm ABA in the bathing medium resulted in 80% inhibition of abaxial but only 45% inhibition of adaxial stomatal opening. Similarly, ABA and Ca2+ each stimulated greater abaxial stomatal closure than adaxial stomatal closure. Whole-cell patch-clamp results showed that the inward K+ currents of abaxial guard cells were inhibited by 60% (−180 mV) in the presence of 1.5 μmCa2+ in the cytoplasm, whereas the inward K+currents of adaxial guard cells were not affected at all by the same treatment. Although 1 μm ABA in the cytoplasm inhibited the inward K+ currents to a similar extent for both abaxial and adaxial guard cells, the former were more sensitive to ABA applied externally. These results suggest that the abaxial stomata are more sensitive to Ca2+ and ABA than adaxial stomata in regard to stomatal opening and closing processes and that the regulation of the inward K+ currents by ABA may not proceed via a Ca2+-signaling pathway in adaxial guard cells. Therefore, there may be different pathways for ABA- and Ca2+-mediated signal transduction in abaxial and adaxial guard cells.
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Contents Summary 1018 I. Introduction 1018 II. Guard cell photosynthesis 1019 III. Guard cell central metabolism 1022 IV. Guard cell starch metabolism differs from that of mesophyll cells and plays a key role in stomatal movement 1025 V. Connectors between mesophyll and guard cells 1026 VI. Challenges and perspectives in understanding and modelling guard cell metabolism 1029 Acknowledgements 1030 References 1030 Summary Stomata are leaf epidermal structures consisting of two guard cells surrounding a pore. Changes in the aperture of this pore regulate plant water‐use efficiency, defined as gain of C by photosynthesis per leaf water transpired. Stomatal aperture is actively regulated by reversible changes in guard cell osmolyte content. Despite the fact that guard cells can photosynthesize on their own, the accumulation of mesophyll‐derived metabolites can seemingly act as signals which contribute to the regulation of stomatal movement. It has been shown that malate can act as a signalling molecule and a counter‐ion of potassium, a well‐established osmolyte that accumulates in the vacuole of guard cells during stomatal opening. By contrast, their efflux from guard cells is an important mechanism during stomatal closure. It has been hypothesized that the breakdown of starch, sucrose and lipids is an important mechanism during stomatal opening, which may be related to ATP production through glycolysis and mitochondrial metabolism, and/or accumulation of osmolytes such as sugars and malate. However, experimental evidence supporting this theory is lacking. Here we highlight the particularities of guard cell metabolism and discuss this in the context of the guard cells themselves and their interaction with the mesophyll cells.
Osmolyte
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Light-gated ion channel
Cys-loop receptors
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Stomata, functionally specialized small pores on the surfaces of leaves, regulate the flow of gases in and out of plants. The pore is opened by an increase in osmotic pressure in the guard cells, resulting in the uptake of water. The subsequent increase in cell volume inflates the guard cell and culminates with the opening of the pore. Although guard cells can be regarded as one of the most thoroughly investigated cell types, our knowledge of the signalling pathways which regulate guard cell function remains fragmented. Recent research in guard cells has led to several new hypotheses, however, it is still a matter of debate as to whether guard cells function autonomously or are subject to regulation by their neighbouring mesophyll cells. This review synthesizes what is known about the mechanisms and genes critical for modulating stomatal movement. Recent progress on the regulation of guard cell function is reviewed here including the involvement of environmental signals such as light, the concentration of atmospheric CO2 and endogenous plant hormones. In addition we re-evaluate the important role of organic acids such as malate and fumarate play in guard cell metabolism in this process.
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Scandium
Carbon fibers
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Summary Stomata can be regarded as hydraulically driven valves in the leaf surface, which open to allow CO 2 uptake and close to prevent excessive loss of water. Movement of these ‘Watergates’ is regulated by environmental conditions, such as light, CO 2 and humidity. Guard cells can sense environmental conditions and function as motor cells within the stomatal complex. Stomatal movement results from the transport of K + salts across the guard cell membranes. In this review, we discuss the biophysical principles and mechanisms of stomatal movement and relate these to ion transport at the plasma membrane and vacuolar membrane. Studies with isolated guard cells, combined with recordings on single guard cells in intact plants, revealed that light stimulates stomatal opening via blue light‐specific and photosynthetic‐active radiation‐dependent pathways. In addition, guard cells sense changes in air humidity and the water status of distant tissues via the stress hormone abscisic acid (ABA). Guard cells thus provide an excellent system to study cross‐talk, as multiple signaling pathways induce both short‐ and long‐term responses in these sensory cells. Contents Summary 665 I. Introduction 665 II. The hydrodynamic valve 666 III. Regulation of ion transport in guard cells 678 IV. Interaction between guard cell signaling pathways 682 V. Outlook 684 Acknowledgements 685 References 685
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Experimental results are presented which show that abscisic acid (ABA) causes stomatal closure only if the stomatal complex is adjacent to live epidermal cells. It is further shown that ABA acts by affecting solute fluxes into and out of epidermal and guard cells. Live epidermal cells function as recipients for solutes and thereby assist their movement out of the guard cells. ABA-mediated solute leakage from guard cells alone does not suffice to cause stomatal closure within one hour.
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