Figure 1. General model of ion fluxes during stomatal opening and closure. Stomatal opening is induced via activation of plasma membrane H+ -ATPase. The protein provides H+ extrusion outside of guard cell which leads to decreased membrane potential (-110 mV) and hyperpolarization. The consequent activation of inward-rectifying K+ channels provides K+ influx. As one of the counter anions, Cl- enters guard cell by symport with H+ , whereas malate is produced in the cytosol. The electrochemical proton gradient across vacuolar membrane is provided by V-Type ATPases which transfers H+ inside the vacuole lumen. Anion channels transport Cl inside the vacuole along the vacuolar electrical potential (-40 mV). A malate carrier maintains cytoplasmic levels of malate decreased. An H+ -driven antiporter takes up K+ against the vacuolar membrane potential. During stomatal closure, K+ efflux through outward rectifying channels causes vacuolar membrane depolarization (0 mV) which is accompanied by Clextrusion through an anion channel. Consequent activation of plasma membrane anion channels provides anion efflux from cytoplasm and depolarization of plasma membrane (-50 mV). Due to membrane potential change, K+ outward-rectifying channels are activated and release K+ .
New Insights into the Regulation of Stomatal Movements by Red Light, Carbon Dioxide and Circadian Rhythms
by Matrosova A. (2015)
Anastasia Matrosova, Faculty of Forest Sciences Department of Forest Genetics and Plant Physiology, Umeå, Sweden
in Doctoral Thesis Swedish University of Agricultural Sciences Umeå 2015 –
Stomata are small adjustable pores formed by pairs of guard cells that enable gas exchange between leaves and the atmosphere, thus directly affecting water loss and CO2 uptake in plants. The current work focuses on the regulation of stomatal movements by red light, carbon dioxide and the circadian system and attempts to uncover molecular mechanisms that control guard cell function. The signaling pathway that underlays stomatal opening in response to red light is yet to be fully elucidated. Here, the HIGH LEAF TEMPERATURE 1 (HT1) protein kinase, known as a negative regulator of high CO2 stomatal closure, is shown to be a key component of stomatal signaling in response to red light (Paper I). It was demonstrated that HT1 is epistatic to the positive regulator of ABA- and high CO2- induced stomatal closure OPEN STOMATA1 (OST1) protein kinase both in red lightand CO2-induced signal transduction in guard cells (Paper I). A photosynthesis-induced drop in intercellular CO2 as well as processes originating in the photosynthetic electron transport chain (PETC) have been proposed to signal the guard cell response to red light. Investigation of the effect of PETC inhibitors on stomatal conductance in Arabidopsis thaliana ecotypes Col-0 and Ely-1a has suggested the redox state of plastoquinone (PQ) pool to be involved in the regulation of stomatal movements (Paper II). The full mechanisms that link the regulation of stomatal movements to the circadian clock are yet unknown. The blue light receptor, F-box protein and key element of the circadian clock ZEITLUPE (ZTL) was here shown to physically interact with OST1 protein kinase (Paper III). Furthermore, Arabidopsis thaliana mutant plants and Populus transgenic lines that lack the activity of ZTL or OST1 demonstrated similar phenotypes, affected in stomatal movement control (Paper III). The work supports a requirement of both ZTL and OST1 in the regulation of guard cell turgor and suggests a direct link between the circadian clock and OST1 activity.