Is Malate an Intermediate in the Signal-Transduction Network of Elevated Co2-Induced Stomatal Closure?

• Other Authors: Jiang, Tianran (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Biology
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-3517

Stomata close when plants are exposed to elevated CO2 concentration and they open when plants are exposed to low CO2 concentration. However, molecular elements of the signal transduction network involved in CO2 sensing have not been identified. In addition to the intrinsic CO2 response that guard cells have, it has been proposed that high CO2 evoked malate release from mesophyll cells activates the guard cell anion channel, which initiates ion efflux. In our experimental system (Vicia faba, 3 h from the onset of illumination when stomatal aperture size is increasing), guard cell K+ content tracked the increase in aperture and therefore activation of the anion channel was the cardinal event in stomatal closure. The time course and concentration of malate required to close stomata were studied using epidermal peels (to determine guard cell sensitivity to malate) and petiolar feeding (to infer apoplastic transport of malate to the guard cells). Isolation of the bulk leaf apoplastic malate pool was additionally studied using a novel sequential sampling method. The malate contents of the guard cell symplast and the guard cell apoplast were determined using quantitative histochemical techniques. During the photoperiod, at stomatal aperture size ≤5 μm, guard cell apoplast malate content (maximum = 0.13 pmol, ~ 31 mM) was negatively correlated with stomatal aperture size (R2 = 0.74), which indicates a regulatory role of malate at low apertures. As the essence of this study, the CO2 concentration around whole plants was elevated two fold from nominal pre industrial CO2 concentration (300 μL·L-1). Consistent with previous studies, the bulk leaf apoplastic malate concentration increased (by 2.6 fold) within 30 min of exposure to elevated CO2 concentration. However, stomata closed and the guard-cell K+ contents declined before the modest increase in the guard cell-apoplast malate content. These results do not support the hypothesis that elevated CO2 induced malate release from mesophyll cells initiates stomatal closure, however, an elevated guard cell apoplast malate content could be a contributing factor in the maintenance of stomatal closure under high CO2 concentration. === A Thesis submitted to the Department of Biology in partial fulfillment of the requirements for the degree of Master of Science. === Spring Semester, 2004. === December 17, 2003. === Vicia Faba, Elevated CO2 Concentration, Guard-Cell, Stomatal Movement === Includes bibliographical references. === William H. Outlaw, Jr., Professor Directing Thesis; Hank W. Bass, Committee Member; George W. Bates, Committee Member; Laura R. Keller, Committee Member.