Prognostic impact of concomitant pH-regulating drugs in patients with non-small cell lung cancer receiving epidermal growth factor receptor tyrosine kinase inhibitors: the Tokushukai REAl-world Data project 01-S1.

PURPOSE: This study aimed to examine the prognostic impact of concomitant pH-regulating drug use in patients with epidermal growth factor receptor (EGFR)-mutation-positive non-small-cell lung cancer (NSCLC) receiving EGFR-tyrosine kinase inhibitors (TKIs). METHODS: We conducted a nationwide retrospective cohort study and reviewed clinical data of consecutive patients with NSCLC treated with the first-line EGFR-TKIs in 46 hospitals between April 2010 and March 2020. Cox regression analyses were conducted to examine the differences in overall survival (OS) between patients treated with and without concomitant pH-regulating drugs, including potassium-competitive acid blockers (P-CABs), proton pump inhibitors (PPIs), and H2-receptor antagonists (H2RAs). RESULTS: A total of 758 patients were included in the final dataset, of which 307 (40%) were administered concomitant pH-regulating drugs while receiving frontline EGFR-TKIs. After adjusting for basic patient characteristics, patients administered gefitinib, erlotinib, afatinib, and osimertinib with concomitant pH-regulating drugs had lower OS than those without concomitant pH-regulating drugs, with hazard ratios of 1.74 (with a 95% confidence interval of 1.34-2.27), 1.33 (0.80-2.22), 1.73 (0.89-3.36), and 5.04 (1.38-18.44), respectively. The 2-year OS rates of patients receiving gefitinib with or without concomitant pH-regulating drugs were 65.4 and 77.5%, those for erlotinib were 55.8 and 66.6%, and those for afatinib were 63.2 and 76.9%, respectively. The 1-year OS rates of patients receiving osimertinib with or without concomitant pH-regulating drugs were 88.1% and 96.9%, respectively. CONCLUSION: In addition to the first-generation EGFR-TKIs, the second- and third-generation EGFR-TKIs also resulted in OS deterioration in patients with EGFR mutation-positive NSCLC when used concurrently with pH-regulating drugs.

Inflammation­based prognostic markers of metastatic pancreatic cancer using real­world data in Japan: The Tokushukai REAl­world Data (TREAD) project.

Inflammation-based prognostic markers based on a combination of blood-based parameters, including the modified Glasgow prognostic score (mGPS), have been associated with clinical outcomes in patients with various types of cancer. The present study aimed to evaluate and compare the accuracy of these previously reported markers in patients with metastatic pancreatic cancer receiving first-line chemotherapy. A total of 846 patients were identified between April 2010 and March 2020 as part of a nationwide real-world study from 46 Tokushukai medical group hospitals in Japan. Blood laboratory data collected within 14 days of starting first-line chemotherapy assessed 17 inflammation-based prognostic markers. Information from patients with no missing data was used to compare the accuracy and performance of the inflammation-based prognostic markers. A total of 487 patients were eligible for this supplemental analysis. The 17 inflammation-based markers demonstrated significant prognostic value. Among them, the concordance rate with overall survival (OS) was highest for mGPS. The median OS time of patients with mGPS 0, 1 and 2 was 8.2, 6.0 and 2.9 months, respectively. Compared with mGPS 0, mGPS 1 and 2 showed hazard ratios of 1.39 (95% confidence interval, 1.07-1.81) and 2.63 (2.00-3.45), respectively. The present real-world data analysis showed that various previously reported inflammation-based markers had significant prognostic value in patients with metastatic pancreatic cancer. Among these markers, the mGPS demonstrated the highest level of accuracy. This trial has been registered in the University Hospital Medical Information Network Clinical Trials Registry as UMIN000050590 on April 1, 2023.

Real-world treatment outcomes of metastatic biliary tract cancer patients in Japan: the Tokushukai REAl-world data project 04 (TREAD 04).

OBJECTIVES: To investigate temporal trends in treatment patterns and prognostic factors for overall survival in patients with metastatic biliary tract cancer. METHODS: From the Tokushukai REAl-world Data project, we identified 945 patients with metastatic biliary tract cancer treated with gemcitabine, tegafur/gimeracil/oteracil, gemcitabine plus cisplatin, gemcitabine plus tegafur/gimeracil/oteracil or gemcitabine plus cisplatin and tegafur/gimeracil/oteracil between April 2010 and March 2022. Stratified/conventional Cox regression analyses were conducted to examine the association between overall survival and patient- and tumour-related factors, study period, hospital volume, hospital type and first-line chemotherapy regimen. Using inverse probability of treatment weighting with propensity scores, overall survival was also compared between monotherapy and combination therapy groups. RESULTS: We enrolled 366 patients (199 men; median age, 72 years). Over a median follow-up of 5.2 months, the median overall survival was 7.0 months (95% confidence interval 6.2-9.0), and the median time to treatment failure was 3.5 months (95% confidence interval 3.1-4.5). Median overall survival and time to treatment failure for gemcitabine/tegafur-gimeracil-oteracil/gemcitabine plus cisplatin/gemcitabine plus tegafur-gimeracil-oteracil/gemcitabine plus cisplatin and tegafur-gimeracil-oteracil regimen were 6.2/6.6/7.9/16.2/15.1 and 2.8/3.4/4.1/15.3/7.4 months, respectively. Primary disease site, previous surgery, previous endoscopic procedures and hospital type were identified as significant prognostic factors. Inverse probability of treatment weighting analysis demonstrated that combination therapy had a significantly better prognosis than monotherapy (hazard ratio 0.61, 95% confidence interval 0.43-0.88, P = 0.006). CONCLUSIONS: Our real-world data analysis showed that standard care for metastatic biliary tract cancer is widely used in hospitals throughout Japan and verified the survival benefits of combination therapy over monotherapy observed in prior clinical trials. CLINICAL TRIAL NUMBER: UMIN000050590 (http://www.umin.ac.jp/ctr/index.htm).

Stepwise prolongation of overall survival from first to third generation EGFR-TKIs for EGFR mutation-positive non-small-cell lung cancer: the Tokushukai REAl-world Data project (TREAD 01).

OBJECTIVE: The introduction of new-generation epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) has afforded promising overall survival outcomes in clinical trials for non-small-cell lung cancer. We aim to investigate the current adoption rate of these agents and the real-world impact on overall survival among institutions. METHODS: In a nationwide retrospective cohort study of 46 Tokushukai Medical Group hospitals in Japan, we analyzed clinical data of consecutive patients with non-small-cell lung cancer receiving EGFR-TKIs between April 2010 and March 2020. Univariate and multivariate Cox regression analyses examined the associations between overall survival and patient/tumor-related factors and first-line EGFR-TKIs. RESULTS: A total of 758 patients (58.5% females; median age, 73 years) were included. Of 40 patients diagnosed in 2010, 72.5% received gefitinib, whereas 81.3% of 107 patients diagnosed in 2019 received osimertinib as the first-line EGFR-TKI. With a median follow-up of 15.8 months, the median overall survival was 28.4 months (95% confidence interval, 15.3-31.0). In a multivariate Cox regression analysis, age, body mass index, disease status, EGFR mutational status and first-line epidermal growth factor receptor tyrosine kinase inhibitor were identified as significant prognostic factors after adjusting for background factors including study period, hospital volume and hospital type. The estimated 2-year overall survival rates for gefitinib, erlotinib, afatinib and osimertinib were 70.1% (95% confidence interval 59.7-82.4), 67.8% (95% confidence interval 55.3-83.2), 75.5% (95% confidence interval 64.7-88.0) and 90.8% (95% confidence interval 84.8-97.3), respectively. The median time to treatment failure of gefitinib, erlotinib, afatinib and osimertinib were 12.8, 8.8, 12.0 and 16.9 months or more, respectively. CONCLUSIONS: Our real-world data revealed that the swift and widespread utilization of newer-generation EGFR-TKIs in patients with EGFR mutation-positive non-small-cell lung cancer, and that these newer-generation EGFR-TKIs can prolong overall survival regardless of hospital volume or type. Therefore, osimertinib could be a reasonable first choice treatment for these patients across various clinical practice settings.

Real­world treatment outcomes among patients with metastatic pancreatic cancer in Japan: The Tokushukai real­world data project.

The present study aimed to investigate temporal trends in treatment patterns and prognostic factors for overall survival (OS) among patients with metastatic pancreatic cancer. From the Tokushukai REAl-world Data project, 1,093 patients with metastatic pancreatic cancer treated with gemcitabine, tegafur/gimeracil/oteracil (S-1), gemcitabine plus S-1, gemcitabine plus nab-paclitaxel, or fluorouracil, folic acid, oxaliplatin and irinotecan (FOLFIRINOX) between April 2010 and March 2020 were identified. Stratified/conventional Cox regression analyses were conducted to examine associations between patient- and tumor-related factors, study period, hospital volume, hospital type and first-line chemotherapy regimens. Overall, 846 patients were selected (503 male patients; median age, 70 years) after excluding ineligible patients. Over a median follow-up of 5.4 months, the median OS was 6.8 months (95% confidence interval, 6.3-7.4). The median OS for gemcitabine, S-1, gemcitabine plus S-1, gemcitabine plus nab-paclitaxel and FOLFIRINOX regimens was 5.9, 5.3, 7.7, 9.0 and 9.5 months, respectively. The median OS for 2010-2013, 2014-2017 and 2017-2020 was 6.2, 7.1 and 7.8 months, respectively. Performance status, body mass index and first-line chemotherapy regimens were identified to be significant prognostic factors. In summary, the real-world data indicated that standard care, including chemotherapy, for metastatic pancreatic cancer was widely used in hospitals throughout Japan and verified the survival benefits of gemcitabine plus nab-paclitaxel and FOLFIRINOX observed in prior clinical trials. This trial has been registered in the University Hospital Medical Information Network Clinical Trials Registry as UMIN000050590 on April 1, 2023.

Real-World Outcomes of Systemic Therapy in Japanese Patients with Cancer (Tokushukai REAl-World Data Project: TREAD): Study Protocol for a Nationwide Cohort Study.

Cohort studies using large-scale databases have become increasingly important in recent years. The Tokushukai Medical Group is a leading medical group in Japan that includes 71 general hospitals nationwide from Hokkaido to Okinawa, with a total of 18,000 beds, and a unified electronic medical record system. This retrospective cohort study aims to evaluate the real-world outcomes of systemic therapy for Japanese patients with cancer using this merit of scale. All adult patients with cancer who received systemic therapy using a centrally registered chemotherapy protocol system at 46 hospitals from April 2010 to March 2020 will be identified (~48,850 patients). Key exclusion criteria include active double cancer and inadequate data extraction. Data will be obtained through electronic medical records, diagnosis procedure combination data, medical prescription data, and the national cancer registration system that includes sociodemographic variables, diagnostic and laboratory tests, concomitant drug prescriptions, cost, and overall survival. Kaplan-Meier estimates will be calculated for time-to-event analyses. Stratified/conventional Cox proportional hazards regression analyses will be conducted to examine the relationships between overall survival and related factors. Our findings provide important insights for future research directions, policy initiatives, medical guidelines, and clinical decision-making.

The evolution of plant proton pump regulation via the R domain may have facilitated plant terrestrialization.

Plasma membrane (PM) H+-ATPases are the electrogenic proton pumps that export H+ from plant and fungal cells to acidify the surroundings and generate a membrane potential. Plant PM H+-ATPases are equipped with a C­terminal autoinhibitory regulatory (R) domain of about 100 amino acid residues, which could not be identified in the PM H+-ATPases of green algae but appeared fully developed in immediate streptophyte algal predecessors of land plants. To explore the physiological significance of this domain, we created in vivo C-terminal truncations of autoinhibited PM H+­ATPase2 (AHA2), one of the two major isoforms in the land plant Arabidopsis thaliana. As more residues were deleted, the mutant plants became progressively more efficient in proton extrusion, concomitant with increased expansion growth and nutrient uptake. However, as the hyperactivated AHA2 also contributed to stomatal pore opening, which provides an exit pathway for water and an entrance pathway for pests, the mutant plants were more susceptible to biotic and abiotic stresses, pathogen invasion and water loss, respectively. Taken together, our results demonstrate that pump regulation through the R domain is crucial for land plant fitness and by controlling growth and nutrient uptake might have been necessary already for the successful water-to-land transition of plants.

A tonoplast-localized magnesium transporter is crucial for stomatal opening in Arabidopsis under high Mg2+ conditions.

Plant stomata play an important role in CO2 uptake for photosynthesis and transpiration, but the mechanisms underlying stomatal opening and closing under changing environmental conditions are still not completely understood. Through large-scale genetic screening, we isolated an Arabidopsis mutant (closed stomata2 (cst2)) that is defective in stomatal opening. We cloned the causal gene (MGR1/CST2) and functionally characterized this gene. The mutant phenotype was caused by a mutation in a gene encoding an unknown protein with similarities to the human magnesium (Mg2+ ) efflux transporter ACDP/CNNM. MGR1/CST2 was localized to the tonoplast and showed transport activity for Mg2+ . This protein was constitutively and highly expressed in guard cells. Knockout of this gene resulted in stomatal closing, decreased photosynthesis and growth retardation, especially under high Mg2+ conditions, while overexpression of this gene increased stomatal opening and tolerance to high Mg2+ concentrations. Furthermore, guard cell-specific expression of MGR1/CST2 in the mutant partially restored its stomatal opening. Our results indicate that MGR1/CST2 expression in the leaf guard cells plays an important role in maintaining cytosolic Mg2+ concentrations through sequestering Mg2+ into vacuoles, which is required for stomatal opening, especially under high Mg2+ conditions.

Type 2C protein phosphatase clade D family members dephosphorylate guard cell plasma membrane H+-ATPase.

Plasma membrane (PM) H+-ATPase in guard cells is activated by phosphorylation of the penultimate residue, threonine (Thr), in response to blue and red light, promoting stomatal opening. Previous in vitro biochemical investigation suggested that Mg2+- and Mn2+-dependent membrane-localized type 2C protein phosphatase (PP2C)-like activity mediates the dephosphorylation of PM H+-ATPase in guard cells. PP2C clade D (PP2C.D) was later demonstrated to be involved in PM H+-ATPase dephosphorylation during auxin-induced cell expansion in Arabidopsis (Arabidopsis thaliana). However, it is unclear whether PP2C.D phosphatases are involved in PM H+-ATPase dephosphorylation in guard cells. Transient expression experiments using Arabidopsis mesophyll cell protoplasts revealed that all PP2C.D isoforms dephosphorylate the endogenous PM H+-ATPase. We further analyzed PP2C.D6/8/9, which display higher expression levels than other isoforms in guard cells, observing that pp2c.d6, pp2c.d8, and pp2c.d9 single mutants showed similar light-induced stomatal opening and phosphorylation status of PM H+-ATPase in guard cells as Col-0. In contrast, the pp2c.d6/9 double mutant displayed wider stomatal apertures and greater PM H+-ATPase phosphorylation in response to blue light, but delayed dephosphorylation of PM H+-ATPase in guard cells; the pp2c.d6/8/9 triple mutant showed similar phenotypes to those of the pp2c.d6/9 double mutant. Taken together, these results indicate that PP2C.D6 and PP2C.D9 redundantly mediate PM H+-ATPase dephosphorylation in guard cells. Curiously, unlike auxin-induced cell expansion in seedlings, auxin had no effect on the phosphorylation status of PM H+-ATPase in guard cells.

A conserved, buried cysteine near the P-site is accessible to cysteine modifications and increases ROS stability in the P-type plasma membrane H+-ATPase.

Sulfur-containing amino acid residues function in antioxidative responses, which can be induced by the reactive oxygen species generated by excessive copper and hydrogen peroxide. In all Na+/K+, Ca2+, and H+ pumping P-type ATPases, a cysteine residue is present two residues upstream of the essential aspartate residue, which is obligatorily phosphorylated in each catalytic cycle. Despite its conservation, the function of this cysteine residue was hitherto unknown. In this study, we analyzed the function of the corresponding cysteine residue (Cys-327) in the autoinhibited plasma membrane H+-ATPase isoform 2 (AHA2) from Arabidopsis thaliana by mutagenesis and heterologous expression in a yeast host. Enzyme kinetics of alanine, serine, and leucine substitutions were identical with those of the wild-type pump but the sensitivity of the mutant pumps was increased towards copper and hydrogen peroxide. Peptide identification and sequencing by mass spectrometry demonstrated that Cys-327 was prone to oxidation. These data suggest that Cys-327 functions as a protective residue in the plasma membrane H+-ATPase, and possibly in other P-type ATPases as well.

Plasma membrane H+-ATPases sustain pollen tube growth and fertilization.

Pollen tubes are highly polarized tip-growing cells that depend on cytosolic pH gradients for signaling and growth. Autoinhibited plasma membrane proton (H+) ATPases (AHAs) have been proposed to energize pollen tube growth and underlie cell polarity, however, mechanistic evidence for this is lacking. Here we report that the combined loss of AHA6, AHA8, and AHA9 in Arabidopsis thaliana delays pollen germination and causes pollen tube growth defects, leading to drastically reduced fertility. Pollen tubes of aha mutants had reduced extracellular proton (H+) and anion fluxes, reduced cytosolic pH, reduced tip-to-shank proton gradients, and defects in actin organization. Furthermore, mutant pollen tubes had less negative membrane potentials, substantiating a mechanistic role for AHAs in pollen tube growth through plasma membrane hyperpolarization. Our findings define AHAs as energy transducers that sustain the ionic circuit defining the spatial and temporal profiles of cytosolic pH, thereby controlling downstream pH-dependent mechanisms essential for pollen tube elongation, and thus plant fertility.

A program of exercise, brain training, and lecture to prevent cognitive decline.

OBJECTIVE: We examined the benefits of a community-based program combining physical exercise, cognitive training, and education on dementia and lifestyle habits. METHODS: This crossover open-label trial included 141 community-dwelling elderly people with suspected mild cognitive decline (MCD). Subjects were assigned to a 6-month intervention-first/6-month observation-second (INT-OBS) group or an OBS-INT group. The 6-month intervention consisted of 2 h of physical exercise, cognitive training, and classroom study or rest once weekly. Primary outcome was change in Touch Panel-type Dementia Assessment Scale (TDAS) score. RESULTS: TDAS score improved significantly during the intervention period compared with the observation period for all subjects (P < 0.05). Some physical functions also improved significantly during the intervention period compared with the observation period in the OBS-INT group (P < 0.05). INTERPRETATION: This community-based program improved both cognitive and physical function in elderly people with suspected MCD.

Raf-like kinases CBC1 and CBC2 negatively regulate stomatal opening by negatively regulating plasma membrane H+-ATPase phosphorylation in Arabidopsis.

Stomatal pores, which are surrounded by pairs of guard cells in the plant epidermis, regulate gas exchange between plants and the atmosphere, thereby controlling photosynthesis and transpiration. Blue light works as a signal to guard cells, to induce intracellular signaling and open stomata. Blue light receptor phototropins (phots) are activated by blue light; phot-mediated signals promote plasma membrane (PM) H+-ATPase activity via C-terminal Thr phosphorylation, serving as the driving force for stomatal opening in guard cells. However, the details of this signaling process are not fully understood. In this study, through an in vitro screening of phot-interacting protein kinases, we obtained the CBC1 and CBC2 that had been reported as signal transducers in stomatal opening. Promoter activities of CBC1 and CBC2 indicated that both genes were expressed in guard cells. Single and double knockout mutants of CBC1 and CBC2 showed no lesions in the context of phot-mediated phototropism, chloroplast movement, or leaf flattening. In contrast, the cbc1cbc2 double mutant showed larger stomatal opening under both dark and blue light conditions. Interestingly, the level of phosphorylation of C-terminal Thr of PM H+-ATPase was higher in double mutant guard cells. The larger stomatal openings of the double mutant were effectively suppressed by the phytohormone abscisic acid (ABA). CBC1 and CBC2 interacted with BLUS1 and PM H+-ATPase in vitro. From these results, we conclude that CBC1 and CBC2 act as negative regulators of stomatal opening, probably via inhibition of PM H+-ATPase activity.

Usefulness of intermittent clomiphene citrate treatment for women with polycystic ovarian syndrome that is resistant to standard clomiphene citrate treatment.

PURPOSE: Clomiphene citrate (CC) has been used as a first-line treatment for anovulatory polycystic ovary syndrome (PCOS). However, some patients with PCOS are resistant to standard CC treatment. In this study, a new CC treatment protocol was developed, named "intermittent CC treatment" (ICT) and its efficacy was investigated on the induction of follicular growth in patients with PCOS who were resistant to standard CC treatment. METHODS: Of the 42 patients with PCOS who were resistant to standard CC treatment (50 mg/day, 5 days), 26 underwent ICT. They were given 100 mg/day of CC for 5 days from the next menstrual cycle day (MCD) 5 (first CC). If follicular growth was not observed on MCD 14, they were given 100 mg/day of CC for 5 days (MCD 14-MCD 18) (second CC). If follicular growth still was not observed on MCD 23, they were treated with CC again in the same way (third CC). RESULTS: The first CC, second CC, and third CC were effective for 3/26 (11.5%) patients, 12/23 (52.2%) patients, and 6/11 (54.5%) patients, respectively. In total, ICT was effective for 21/26 (80.8%) patients with CC-resistant PCOS. CONCLUSION: Thus, ICT is a useful treatment and could be an alternative to gonadotropin therapy for patients with CC-resistant PCOS.

Brassinosteroid Involvement in Arabidopsis thaliana Stomatal Opening.

Stomata within the plant epidermis regulate CO2 uptake for photosynthesis and water loss through transpiration. Stomatal opening in Arabidopsis thaliana is determined by various factors, including blue light as a signal and multiple phytohormones. Plasma membrane transporters, including H+-ATPase, K+ channels and anion channels in guard cells, mediate these processes, and the activities and expression levels of these components determine stomatal aperture. However, the regulatory mechanisms involved in these processes are not fully understood. In this study, we used infrared thermography to isolate a mutant defective in stomatal opening in response to light. The causative mutation was identified as an allele of the brassinosteroid (BR) biosynthetic mutant dwarf5. Guard cells from this mutant exhibited normal H+-ATPase activity in response to blue light, but showed reduced K+ accumulation and inward-rectifying K+ (K+in) channel activity as a consequence of decreased expression of major K+in channel genes. Consistent with these results, another BR biosynthetic mutant, det2-1, and a BR receptor mutant, bri1-6, exhibited reduced blue light-dependent stomatal opening. Furthermore, application of BR to the hydroponic culture medium completely restored stomatal opening in dwarf5 and det2-1 but not in bri1-6. However, application of BR to the epidermis of dwarf5 did not restore stomatal response. From these results, we conclude that endogenous BR acts in a long-term manner and is required in guard cells with the ability to open stomata in response to light, probably through regulation of K+in channel activity.

A Raf-like protein kinase BHP mediates blue light-dependent stomatal opening.

Stomata in the plant epidermis open in response to blue light and affect photosynthesis and plant growth by regulating CO2 uptake and transpiration. In stomatal guard cells under blue light, plasma membrane H+-ATPase is phosphorylated and activated via blue light-receptor phototropins and a signaling mediator BLUS1, and H+-ATPase activation drives stomatal opening. However, details of the signaling between phototropins and H+-ATPase remain largely unknown. In this study, through a screening of specific inhibitors for the blue light-dependent H+-ATPase phosphorylation in guard cells, we identified a Raf-like protein kinase, BLUE LIGHT-DEPENDENT H+-ATPASE PHOSPHORYLATION (BHP). Guard cells in the bhp mutant showed impairments of stomatal opening and H+-ATPase phosphorylation in response to blue light. BHP is abundantly expressed in the cytosol of guard cells and interacts with BLUS1 both in vitro and in vivo. Based on these results, BHP is a novel signaling mediator in blue light-dependent stomatal opening, likely downstream of BLUS1.

GOLDEN 2-LIKE transcription factors for chloroplast development affect ozone tolerance through the regulation of stomatal movement.

Stomatal movements regulate gas exchange, thus directly affecting the efficiency of photosynthesis and the sensitivity of plants to air pollutants such as ozone. The GARP family transcription factors GOLDEN 2-LIKE1 (GLK1) and GLK2 have known functions in chloroplast development. Here, we show that Arabidopsis thaliana (A. thaliana) plants expressing the chimeric repressors for GLK1 and -2 (GLK1/2-SRDX) exhibited a closed-stomata phenotype and strong tolerance to ozone. By contrast, plants that overexpress GLK1/2 exhibited an open-stomata phenotype and higher sensitivity to ozone. The plants expressing GLK1-SRDX had reduced expression of the genes for inwardly rectifying K(+) (K(+) in) channels and reduced K(+) in channel activity. Abscisic acid treatment did not affect the stomatal phenotype of 35S:GLK1/2-SRDX plants or the transcriptional activity for K(+) in channel gene, indicating that GLK1/2 act independently of abscisic acid signaling. Our results indicate that GLK1/2 positively regulate the expression of genes for K(+) in channels and promote stomatal opening. Because the chimeric GLK1-SRDX repressor driven by a guard cell-specific promoter induced a closed-stomata phenotype without affecting chloroplast development in mesophyll cells, modulating GLK1/2 activity may provide an effective tool to control stomatal movements and thus to confer resistance to air pollutants.

Difference in abscisic acid perception mechanisms between closure induction and opening inhibition of stomata.

Abscisic acid (ABA) induces stomatal closure and inhibits light-induced stomatal opening. The mechanisms in these two processes are not necessarily the same. It has been postulated that the ABA receptors involved in opening inhibition are different from those involved in closure induction. Here, we provide evidence that four recently identified ABA receptors (PYRABACTIN RESISTANCE1 [PYR1], PYRABACTIN RESISTANCE-LIKE1 [PYL1], PYL2, and PYL4) are not sufficient for opening inhibition in Arabidopsis (Arabidopsis thaliana). ABA-induced stomatal closure was impaired in the pyr1/pyl1/pyl2/pyl4 quadruple ABA receptor mutant. ABA inhibition of the opening of the mutant's stomata remained intact. ABA did not induce either the production of reactive oxygen species and nitric oxide or the alkalization of the cytosol in the quadruple mutant, in accordance with the closure phenotype. Whole cell patch-clamp analysis of inward-rectifying K(+) current in guard cells showed a partial inhibition by ABA, indicating that the ABA sensitivity of the mutant was not fully impaired. ABA substantially inhibited blue light-induced phosphorylation of H(+)-ATPase in guard cells in both the mutant and the wild type. On the other hand, in a knockout mutant of the SNF1-related protein kinase, srk2e, stomatal opening and closure, reactive oxygen species and nitric oxide production, cytosolic alkalization, inward-rectifying K(+) current inactivation, and H(+)-ATPase phosphorylation were not sensitive to ABA.

Crosstalk between blue-light- and ABA-signaling pathways in stomatal guard cells.

We recently established an immunohistochemical method for the detection of blue light (BL)-induced and phototropin-mediated phosphorylation of plasma-membrane H+-ATPase in stomatal guard cells of Arabidopsis thaliana. This technique makes it possible to detect the phosphorylation/activation status of guard-cell H+-ATPase in the epidermis of a single rosette leaf, without the need to prepare guard-cell protoplasts (GCPs) from a large number of plants. Moreover, it can detect guard-cell responses under more natural and stress-free conditions compared to using GCPs. Taking advantage of these properties, we examined the effect of abscisic acid (ABA) on BL-induced phosphorylation of guard-cell H+-ATPase by using ABA-insensitive mutants. This revealed inhibition of BL-induced phosphorylation of guard-cell H+-ATPase via the early ABA-signaling components PYR/PYL/RCAR-PP2Cs-SnRK2s, which are known to be early ABA-signaling components for a wide range of ABA responses in plants.