Reactive Carbonyl Species Mediate Methyl Jasmonate-Induced Stomatal Closure.

Production of reactive oxygen species (ROS) is a key signal event for methyl jasmonate (MeJA)- and abscisic acid (ABA)-induced stomatal closure. We recently showed that reactive carbonyl species (RCS) stimulates stomatal closure as an intermediate downstream of hydrogen peroxide (H2O2) production in the ABA signaling pathway in guard cells of Nicotiana tabacum and Arabidopsis thaliana. In this study, we examined whether RCS functions as an intermediate downstream of H2O2 production in MeJA signaling in guard cells using transgenic tobacco plants overexpressing A. thaliana 2-alkenal reductase (n-alkanal + NAD(P)+ ⇌ 2-alkenal + NAD(P)H + H+) (AER-OE tobacco) and Arabidopsis plants. The stomatal closure induced by MeJA was impaired in the AER-OE tobacco and was inhibited by RCS scavengers, carnosine and pyridoxamine, in the wild-type (WT) tobacco plants and Arabidopsis plants. Application of MeJA significantly induced the accumulation of RCS, including acrolein and 4-hydroxy-(E)-2-nonenal, in the WT tobacco but not in the AER-OE plants. Application of MeJA induced H2O2 production in the WT tobacco and the AER-OE plants and the H2O2 production was not inhibited by the RCS scavengers. These results suggest that RCS functions as an intermediate downstream of ROS production in MeJA signaling and in ABA signaling in guard cells.

Exogenous proline enhances antioxidant enzyme activities but does not mitigate growth inhibition by selenate stress in tobacco BY-2 cells.

Selenium (Se) causes oxidative damage to plants. Proline is accumulated as a compatible solute in plants under stress conditions and mitigates stresses. Selenate at 250 µM increased cell death and inhibited the growth of tobacco BY-2 cells while exogenous proline at 10 mM did not mitigate the inhibition by selenate. Selenate increased accumulation of Se and ROS and activities of antioxidant enzymes but not lipid peroxidation in the BY-2 cells. Proline increased Se accumulation and antioxidant enzyme activities but not either ROS accumulation or lipid peroxidation in the selenate-stressed cells. Glutathione (GSH) rather than ascorbic acid (AsA) mitigated the growth inhibition although both reduced the accumulation of ROS induced by selenate. These results indicate that proline increases both antioxidant enzyme activities and Se accumulation, which overall fails to ameliorate the growth inhibition by selenate and that the growth inhibition is not accounted for only by ROS accumulation. Abbreviations: APX: ascorbate peroxidase; AsA: ascorbic acid; BY-2: Bright Yellow-2; CAT: catalase; DAI: days after inoculation; DW: dry weight; FW: fresh weight; GSH: glutathione; ROS: reactive oxygen species.

Reactive Carbonyl Species Function as Signal Mediators Downstream of H2O2 Production and Regulate [Ca2+]cyt Elevation in ABA Signal Pathway in Arabidopsis Guard Cells.

We have demonstrated that reactive carbonyl species (RCS) function as an intermediate downstream of hydrogen peroxide (H2O2) production in abscisic acid (ABA) signaling for stomatal closure in guard cells using transgenic tobacco plants overexpressing alkenal reductase. We investigated the conversion of the RCS production into downstream signaling events in the guard cells. Both ABA and H2O2 induced production of the RCS, such as acrolein and 4-hydroxy-(E)-2-nonenal (HNE), in epidermal tissues of wild-type Arabidopsis thaliana plants. Application of the RCS scavengers, carnosine and pyridoxamine, did not affect the ABA-induced H2O2 production but inhibited the ABA- and H2O2-induced stomatal closure. Both acrolein and HNE induced stomatal closure in a plasma membrane NAD(P)H oxidase mutant atrbohD atrbohF as well as in the wild type, but not in a calcium-dependent kinase mutant cpk6. Acrolein activated plasma membrane Ca2+-permeable cation channels, triggered cytosolic free Ca2+ concentration ([Ca2+]cyt) elevation, and induced stomatal closure accompanied by depletion of glutathione in the guard cells. These results suggest that RCS production is a signaling event between the ROS production and [Ca2+]cyt elevation during guard cell ABA signaling.

Reactive Carbonyl Species Mediate ABA Signaling in Guard Cells.

Drought is responsible for a massive reduction in crop yields. In response to drought, plants synthesize the hormone ABA, which induces stomatal closure, thus reducing water loss. In guard cells, ABA triggers production of reactive oxygen species (ROS), which is mediated by NAD(P)H oxidases. The production of ROS is a key factor for ABA-induced stomatal closure, but it remains to be clarified how the production of ROS is transduced into downstream signaling components in guard cells. We investigated roles of reactive carbonyl species (RCS) in ABA-induced stomatal closure using transgenic tobacco (Nicotiana tabacum) overexpressing Arabidopsis 2-alkenal reductase (AER-OE), which scavenges RCS. ABA and hydrogen peroxide (H2O2) induced accumulation of RCS including acrolein and 4-hydroxy-(E)-2-nonenal in wild-type tobacco but not in AER-OE. Stomatal closure and RCS accumulation in response to ABA and H2O2 were inhibited in AER-OE unlike in the wild type, while ABA-induced H2O2 production in guard cells was observed in AER-OE as well as in the wild type. Moreover, ABA inhibited inward-rectifying K+ channels in wild-type guard cells but not in AER-OE guard cells. These results suggest that RCS is involved in ABA-induced stomatal closure and functions downstream of H2O2 production in the ABA signaling pathway in guard cells.

Inhibition by acrolein of light-induced stomatal opening through inhibition of inward-rectifying potassium channels in Arabidopsis thaliana.

Acrolein is a reactive α,ß-unsaturated aldehyde derived from lipid peroxides, which are produced in plants under a variety of stress. We investigated effects of acrolein on light-induced stomatal opening using Arabidopsis thaliana. Acrolein inhibited light-induced stomatal opening in a dose-dependent manner. Acrolein at 100 µM inhibited plasma membrane inward-rectifying potassium (Kin) channels in guard cells. Acrolein at 100 µM inhibited Kin channel KAT1 expressed in a heterologous system using Xenopus leaves oocytes. These results suggest that acrolein inhibits light-induced stomatal opening through inhibition of Kin channels in guard cells.

Catalases CAT1 and CAT3 are not key enzymes in alleviating gamma irradiation-induced DNA damage, H2O2 accumulation, or lipid peroxidation in Arabidopsis thaliana.

Gamma irradiation increased catalase activities at 0.1 kGy and decreased them at 10 kGy in Arabidopsis wild type and catalase-deficient mutants, cat3-1 and cat1 cat3. Irradiation induced DNA damage, H2O2 accumulation, and lipid peroxidation in both mutants as well as the wild type. Thus catalases might not be key enzymes protecting gamma irradiation-induced damage.