The discovery of cytosolic ABA receptors is an important breakthrough in stomatal research; signaling via these receptors is involved in determining the basal stomatal conductance and stomatal responsiveness. However,...The discovery of cytosolic ABA receptors is an important breakthrough in stomatal research; signaling via these receptors is involved in determining the basal stomatal conductance and stomatal responsiveness. However, the source of ABA in guard cells is still not fully understood. The level of ABA increases in guard cells by de novo synthesis, recycling from inactive conjugates via β-glucosidases BG1 and BG2 and by import, whereas it decreases by hydroxylation, conjugation, and export. ABA importers include the NRT1/PTR family protein AIT1, ATP-binding cassette protein ABCG40, and possibly ABCG22, whereas the DTX family member DTX50 and ABCG25 function as ABA exporters. Here, we review the proteins involved in ABA transport and homeostasis and their physiological role in stomatal regulation. Recent experiments suggest that functional redundancy probably exists among ABA transporters between vascu- lature and guard cells and ABA recycling proteins, as stomatal functioning remained intact in abcg22, abcg25, abcg40, aitl, and bglbg2 mutants. Only the initial response to reduced air humidity was significantly delayed in abcg22. Considering the reports showing autonomous ABA synthesis in guard cells, we discuss that rapid stomatal responses to atmospheric factors might depend primarily on guard cellsynthesized ABA, whereas in the case of long-term soil water deficit, ABA synthesized in the vasculature might have a significant role.展开更多
Guard cell ABA signaling is central for the regulation of plant stomatal conductance （gs） and responses to environmental factors （Mer.ilo et al., 2013）; however, the source of ABA is still debatable. Generally, AB...Guard cell ABA signaling is central for the regulation of plant stomatal conductance （gs） and responses to environmental factors （Mer.ilo et al., 2013）; however, the source of ABA is still debatable. Generally, ABA levels are regulated by （1） biosynthesis： de novo and recycling from the inactive conjugates by β-glucosidases BG1 and BG2; （2） catabolism： irreversible hydroxylation and reversible conjugation to ABA glucosyl ester （ABA-GE）; and （3） transport from elsewhere in the plant. Here, we report that the stomatal responses to elevated CO2 concentration, reduced air humidity, and exogenous ABA in different mutants of ABA transport and recycling were generally intact except in abcg22 mutant. ABCG22 was required for initiating reduced air humidityinduced stomatal closure. Thus, either ABA transport into guard cells is not critical for the studied responses or there are several proteins with redundant functions that are responsible for ABA transport.展开更多
文摘The discovery of cytosolic ABA receptors is an important breakthrough in stomatal research; signaling via these receptors is involved in determining the basal stomatal conductance and stomatal responsiveness. However, the source of ABA in guard cells is still not fully understood. The level of ABA increases in guard cells by de novo synthesis, recycling from inactive conjugates via β-glucosidases BG1 and BG2 and by import, whereas it decreases by hydroxylation, conjugation, and export. ABA importers include the NRT1/PTR family protein AIT1, ATP-binding cassette protein ABCG40, and possibly ABCG22, whereas the DTX family member DTX50 and ABCG25 function as ABA exporters. Here, we review the proteins involved in ABA transport and homeostasis and their physiological role in stomatal regulation. Recent experiments suggest that functional redundancy probably exists among ABA transporters between vascu- lature and guard cells and ABA recycling proteins, as stomatal functioning remained intact in abcg22, abcg25, abcg40, aitl, and bglbg2 mutants. Only the initial response to reduced air humidity was significantly delayed in abcg22. Considering the reports showing autonomous ABA synthesis in guard cells, we discuss that rapid stomatal responses to atmospheric factors might depend primarily on guard cellsynthesized ABA, whereas in the case of long-term soil water deficit, ABA synthesized in the vasculature might have a significant role.
文摘Guard cell ABA signaling is central for the regulation of plant stomatal conductance （gs） and responses to environmental factors （Mer.ilo et al., 2013）; however, the source of ABA is still debatable. Generally, ABA levels are regulated by （1） biosynthesis： de novo and recycling from the inactive conjugates by β-glucosidases BG1 and BG2; （2） catabolism： irreversible hydroxylation and reversible conjugation to ABA glucosyl ester （ABA-GE）; and （3） transport from elsewhere in the plant. Here, we report that the stomatal responses to elevated CO2 concentration, reduced air humidity, and exogenous ABA in different mutants of ABA transport and recycling were generally intact except in abcg22 mutant. ABCG22 was required for initiating reduced air humidityinduced stomatal closure. Thus, either ABA transport into guard cells is not critical for the studied responses or there are several proteins with redundant functions that are responsible for ABA transport.
