@article{NuhkatBroscheStoezleFeixetal.2021,
  author    = {Nuhkat, Maris and Brosch{\´e}, Mikael and Stoezle-Feix, Sonja and Dietrich, Petra and Hedrich, Rainer and Roelfsema, M. Rob G. and Kollist, Hannes},
  title     = {Rapid depolarization and cytosolic calcium increase go hand-in-hand in mesophyll cells' ozone response},
  series = {New Phytologist},
  volume    = {232},
  journal   = {New Phytologist},
  number    = {4},
  doi       = {10.1111/nph.17711},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-259646},
  pages     = {1692-1702},
  year      = {2021},
  abstract  = {Plant stress signalling involves bursts of reactive oxygen species (ROS), which can be mimicked by the application of acute pulses of ozone. Such ozone-pulses inhibit photosynthesis and trigger stomatal closure in a few minutes, but the signalling that underlies these responses remains largely unknown. We measured changes in Arabidopsis thaliana gas exchange after treatment with acute pulses of ozone and set up a system for simultaneous measurement of membrane potential and cytosolic calcium with the fluorescent reporter R-GECO1. We show that within 1 min, prior to stomatal closure, O\(_{3}\) triggered a drop in whole-plant CO\(_{2}\) uptake. Within this early phase, O\(_{3}\) pulses (200-1000 ppb) elicited simultaneous membrane depolarization and cytosolic calcium increase, whereas these pulses had no long-term effect on either stomatal conductance or photosynthesis. In contrast, pulses of 5000 ppb O\(_{3}\) induced cell death, systemic Ca\(^{2+}\) signals and an irreversible drop in stomatal conductance and photosynthetic capacity. We conclude that mesophyll cells respond to ozone in a few seconds by distinct pattern of plasma membrane depolarizations accompanied by an increase in the cytosolic calcium ion (Ca\(^{2+}\)) level. These responses became systemic only at very high ozone concentrations. Thus, plants have rapid mechanism to sense and discriminate the strength of ozone signals.},
  language  = {en}
}
@article{HuangDingRoelfsemaetal.2021,
  author    = {Huang, Shouguang and Ding, Meiqi and Roelfsema, M. Rob G. and Dreyer, Ingo and Scherzer, S{\"o}nke and Al-Rasheid, Khaled A. S and Gao, Shiqiang and Nagel, Georg and Hedrich, Rainer and Konrad, Kai R.},
  title     = {Optogenetic control of the guard cell membrane potential and stomatal movement by the light-gated anion channel GtACR1},
  series = {Science Advances},
  volume    = {7},
  journal   = {Science Advances},
  number    = {28},
  doi       = {10.1126/sciadv.abg4619},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-260925},
  year      = {2021},
  abstract  = {Guard cells control the aperture of plant stomata, which are crucial for global fluxes of CO\(_2\) and water. In turn, guard cell anion channels are seen as key players for stomatal closure, but is activation of these channels sufficient to limit plant water loss? To answer this open question, we used an optogenetic approach based on the light-gated anion channelrhodopsin 1 (GtACR1). In tobacco guard cells that express GtACR1, blue- and green-light pulses elicit Cl\(^-\) and NO\(_3\)\(^-\) currents of -1 to -2 nA. The anion currents depolarize the plasma membrane by 60 to 80 mV, which causes opening of voltage-gated K+ channels and the extrusion of K+. As a result, continuous stimulation with green light leads to loss of guard cell turgor and closure of stomata at conditions that provoke stomatal opening in wild type. GtACR1 optogenetics thus provides unequivocal evidence that opening of anion channels is sufficient to close stomata.},
  language  = {en}
}
@article{JakobsonVaahteraToldseppetal.2016,
  author    = {Jakobson, Liina and Vaahtera, Lauri and T{\~o}ldsepp, Kadri and Nuhkat, Maris and Wang, Cun and Wang, Yuh-Shuh and H{\~o}rak, Hanna and Valk, Ervin and Pechter, Priit and Sindarovska, Yana and Tang, Jing and Xiao, Chuanlei and Xu, Yang and Talas, Ulvi Gerst and Garc{\´i}a-Sosa, Alfonso T. and Kangasj{\"a}rvi, Saijaliisa and Maran, Uko and Remm, Maido and Roelfsema, M. Rob G. and Hu, Honghong and Kangasj{\"a}rvi, Jaakko and Loog, Mart and Schroeder, Julian I. and Kollist, Hannes and Brosch{\´e}, Mikael},
  title     = {Natural Variation in Arabidopsis Cvi-0 Accession Reveals an Important Role of MPK12 in Guard Cell CO\(_{2}\) Signaling},
  series = {PLoS Biology},
  volume    = {14},
  journal   = {PLoS Biology},
  number    = {12},
  doi       = {10.1371/journal.pbio.2000322},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-166657},
  pages     = {e2000322},
  year      = {2016},
  abstract  = {Plant gas exchange is regulated by guard cells that form stomatal pores. Stomatal adjustments are crucial for plant survival; they regulate uptake of CO\(_{2}\) for photosynthesis, loss of water, and entrance of air pollutants such as ozone. We mapped ozone hypersensitivity, more open stomata, and stomatal CO\(_{2}\)-insensitivity phenotypes of the Arabidopsis thaliana accession Cvi-0 to a single amino acid substitution in MITOGEN-ACTIVATED PROTEIN (MAP) KINASE 12 (MPK12). In parallel, we showed that stomatal CO\(_{2}\)-insensitivity phenotypes of a mutant cis (CO\(_{2}\)-insensitive) were caused by a deletion of MPK12. Lack of MPK12 impaired bicarbonate-induced activation of S-type anion channels. We demonstrated that MPK12 interacted with the protein kinase HIGH LEAF TEMPERATURE 1 (HT1)—a central node in guard cell CO\(_{2}\) signaling—and that MPK12 functions as an inhibitor of HT1. These data provide a new function for plant MPKs as protein kinase inhibitors and suggest a mechanism through which guard cell CO\(_{2}\) signaling controls plant water management.},
  language  = {en}
}
@article{DindasDreyerHuangetal.2021,
  author    = {Dindas, Julian and Dreyer, Ingo and Huang, Shouguang and Hedrich, Rainer and Roelfsema, M. Rob G.},
  title     = {A voltage-dependent Ca\(^{2+}\) homeostat operates in the plant vacuolar membrane},
  series = {New Phytologist},
  volume    = {230},
  journal   = {New Phytologist},
  number    = {4},
  doi       = {10.1111/nph.17272},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-259627},
  pages     = {1449-1460},
  year      = {2021},
  abstract  = {Cytosolic calcium signals are evoked by a large variety of biotic and abiotic stimuli and play an important role in cellular and long distance signalling in plants. While the function of the plasma membrane in cytosolic Ca\(^{2+}\) signalling has been intensively studied, the role of the vacuolar membrane remains elusive. A newly developed vacuolar voltage clamp technique was used in combination with live-cell imaging, to study the role of the vacuolar membrane in Ca\(^{2+}\) and pH homeostasis of bulging root hair cells of Arabidopsis. Depolarisation of the vacuolar membrane caused a rapid increase in the Ca\(^{2+}\) concentration and alkalised the cytosol, while hyperpolarisation led to the opposite responses. The relationship between the vacuolar membrane potential, the cytosolic pH and Ca2+ concentration suggests that a vacuolar H\(^{+}\)/Ca\(^{2+}\) exchange mechanism plays a central role in cytosolic Ca2+ homeostasis. Mathematical modelling further suggests that the voltage-dependent vacuolar Ca\(^{2+}\) homeostat could contribute to calcium signalling when coupled to a recently discovered K\(^{+}\) channel-dependent module for electrical excitability of the vacuolar membrane.},
  language  = {en}
}