There are several intertwined signaling pathways in the guard cell that regulate ion channel activity and modulate stomatal movements in response to environmental stimuli. Upon environmental stimuli such as drought, ABA production in the guard cell increases and elevates cytosolic calcium concentrations, initiating a cascade of signaling events, thereby leading to ion effluxes outside the guard cell, reducing the turgor pressure and stomata closure which occurs to maintain water balance in plants. Abscisic acid (ABA) regulates the cellular activities that coordinate anion effluxes, inhibits K + in channels, and activates K + out channels in a signaling pathway mediated by ABA receptors, phosphatases/kinases, and ion channels. It has been proposed that the activation of the S-type anion channel SLAC1 in the guard cells is a key event leading to the closing of stomata pores. On the other hand, stomatal closure requires a coordinated efflux of anions and potassium ions from the guard cell via anion channels such as S-type slow activated anion channels (S-type), R-type rapidly activated anion channels (R-type), and K + out outward-rectifying potassium (K + out) channels. In Arabidopsis thaliana, KAT1 and KAT2 channel activity represents a major contributor to a potassium influx in the guard cell. Light-induced stomatal opening is governed by K + in (inward-rectifying potassium) channels present in the PM of the guard cells, such as KAT1, KAT2, AKT1, and AKT2. Stomata movements are achieved via ion fluxes to control guard cell turgor pressure in response to environmental stimuli with a highly sophisticated signaling network that controls cation and anion channels located in the PM (plasma membrane) and tonoplast of the guard cell and is responsible for tuning the stomatal movement. Stomata opening is induced by light, allowing a CO 2 influx during photosynthesis in the leaves, whereas stomata pore closure occurs when plants are exposed to water-deprived conditions to keep the water balance in plants maintained. It is comprised of two kidney-shaped cells forming a stomatal pore in the plant leaf epidermis and is responsible for gaseous exchange between the plants and the surrounding environment. The guard cell plays an essential role in plants when adapting to such environmental stimuli, which are on the rise due to global warming. Plants must adapt to different environmental challenges such as drought, elevated CO 2 and O 3, and pathogen attacks to survive. In this review, the guard cell ion channels are discussed, highlighting the structure and functions of key ion channels the SLAC1 anion channel and KAT1 potassium channel, and their regulatory components, emphasizing their significance in guard cell response to various stimuli. It is well-established that the turgor pressure of guard cells is regulated by ions transportation across the membrane, such as anions and potassium ions. This phenomenon involves a complex network of ion channels and their regulation. When the plants are exposed to extreme weather conditions such as high CO 2 levels, O 3, low air humidity, and drought, the turgor pressure of the guard cells exhibits an appropriate response against these stresses, which leads to stomatal closure. These pores must be tightly controlled, as inadequate CO 2 intake and excessive water loss are devastating for plants. A stomatal pore is formed by a pair of specialized guard cells and serves as a major gateway for water transpiration and atmospheric CO 2 influx for photosynthesis in plants.
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