The responses of guard and mesophyll cell photosynthesis to CO2, O2, light, and water stress in a range of species are similar.

High resolution chlorophyll a fluorescence imaging was used to compare the photosynthetic efficiency of PSII electron transport (estimated by Fq'/Fm') in guard cell chloroplasts and the underlying mesophyll in intact leaves of six different species: Commelina communis, Vicia faba, Amaranthus caudatus, Polypodium vulgare, Nicotiana tabacum, and Tradescantia albifora. While photosynthetic efficiency varied between the species, the efficiencies of guard cells and mesophyll cells were always closely matched. As measurement light intensity was increased, guard cells from the lower leaf surfaces of C. communis and V. faba showed larger reductions in photosynthetic efficiency than those from the upper surfaces. In these two species, guard cell photosynthetic efficiency responded similarly to that of the mesophyll when either light intensity or CO2 concentration during either measurement or growth was changed. In all six species, reducing the O2 concentration from 21% to 2% reduced guard cell photosynthetic efficiency, even for the C4 species A. caudatus, although the mesophyll of the C4 species did not show any O2 modulation of photosynthetic efficiency. This suggests that Rubisco activity is significant in the guard cells of these six species. When C. communis plants were water-stressed, the guard cell photosynthetic efficiency declined in parallel with that of the mesophyll. It was concluded that the photosynthetic efficiency in guard cells is determined by the same factors that determine it in the mesophyll.

[1]  O. Heath,et al.  STUDIES IN STOMATAL BEHAVIOUR , 1952 .

[2]  G. Underwood,et al.  In vivo estimation of the photosystem II photochemical efficiency of individual microphytobenthic cells using high‐resolution imaging of chlorophyll a fluorescence , 2000 .

[3]  D. Bowling,et al.  Influence of the Mesophyll on Stomatal Opening , 1995 .

[4]  L. D. Talbott,et al.  Sugar and Organic Acid Accumulation in Guard Cells of Vicia faba in Response to Red and Blue Light , 1993, Plant physiology.

[5]  T Lawson,et al.  High resolution imaging of photosynthetic activities of tissues, cells and chloroplasts in leaves. , 2001, Journal of experimental botany.

[6]  L. D. Talbott,et al.  The guard cell chloroplast: a perspective for the twenty-first century. , 2002, The New phytologist.

[7]  P. Lu,et al.  A New Mechanism for the Regulation of Stomatal Aperture Size in Intact Leaves (Accumulation of Mesophyll-Derived Sucrose in the Guard-Cell Wall of Vicia faba) , 1997, Plant physiology.

[8]  A. Melis,et al.  Chlorophyll a Fluorescence Transients in Mesophyll and Guard Cells : MODULATION OF GUARD CELL PHOTOPHOSPHORYLATION BY CO(2). , 1982, Plant Physiology.

[9]  S. Assmann,et al.  Apparent absence of a redox requirement for blue light activation of pump current in broad bean guard cells. , 2001, Plant physiology.

[10]  I. R. Cowan,et al.  Stomatal conductance correlates with photosynthetic capacity , 1979, Nature.

[11]  W. H. Outlaw,et al.  Transpiration rate. An important factor controlling the sucrose content of the guard cell apoplast of broad bean. , 2001, Plant physiology.

[12]  A. Jarvis,et al.  The coupled response of stomatal conductance to photosynthesis and transpiration , 1998 .

[13]  N. Baker,et al.  An instrument capable of imaging chlorophyll a fluorescence from intact leaves at very low irradiance and at cellular and subcellular levels of organization , 1997 .

[14]  R. Hedrich,et al.  New approach of monitoring changes in chlorophyll a fluorescence of single guard cells and protoplasts in response to physiological stimuli , 1999 .

[15]  J. Mayo,et al.  The occurrence of functional non-chlorophyllous guard cells in Paphiopedilum spp. , 1975 .

[16]  S. Assmann.  The cellular basis of guard cell sensing of rising CO2 , 1999 .

[17]  O. Heath,et al.  Studies in Stomatal Behaviour VI. AN INVESTIGATION OF THE LIGHT RESPONSES OF WHEAT STOMATA WITH THE ATTEMPTED ELIMINATION OF CONTROL BY THE MESOPHYLL , 1954 .

[18]  K. Shimazaki,et al.  Photosynthetic properties of adaxial guard cells from Vicia leaves , 1997 .

[19]  Graham D. Farquhar,et al.  An Empirical Model of Stomatal Conductance , 1984 .

[20]  B. Drake,et al.  MORE EFFICIENT PLANTS: A Consequence of Rising Atmospheric CO2? , 1997, Annual review of plant physiology and plant molecular biology.

[21]  J. Berry,et al.  Effects of O(2) and CO(2) Concentration on the Steady-State Fluorescence Yield of Single Guard Cell Pairs in Intact Leaf Discs of Tradescantia albiflora: Evidence for Rubisco-Mediated CO(2) Fixation and Photorespiration in Guard Cells. , 1992, Plant physiology.

[22]  R. Scheibe,et al.  Rubisco activity in guard cells compared with the solute requirement for stomatal opening. , 1990, Plant physiology.

[23]  L. D. Talbott,et al.  Central Roles for Potassium and Sucrose in Guard-Cell Osmoregulation , 1996, Plant physiology.

[24]  O. Ueno,et al.  Ultrastructural localization of photosynthetic and photorespiratory enzymes in epidermal, mesophyll, bundle sheath, and vascular bundle cells of the C4 dicot Amaranthus viridis. , 2001, Journal of experimental botany.

[25]  K. Tanaka,et al.  Calvin-Benson Cycle Enzymes in Guard-Cell Protoplasts from Vicia faba L: Implications for the Greater Utilization of Phosphoglycerate/Dihydroxyacetone Phosphate Shuttle between Chloroplasts and the Cytosol. , 1989, Plant physiology.

[26]  Govindjee,et al.  Effects of Cations and Abscisic Acid on Chlorophyll a Fluorescence in Guard Cells of Vicia faba. , 1982, Plant physiology.

[27]  S. Assmann,et al.  Photosynthesis by Guard Cell Chloroplasts of Vicia faba L.: Effects of Factors Associated with Stomatal Movement , 1993 .

[28]  S. Gepstein,et al.  Immunological evidence for the presence of ribulose bisphosphate carboxylase in guard cell chloroplasts. , 1985, Plant physiology.

[29]  S. Taylor,et al.  Photosynthetic Carbon Fixation in Guard Cell Protoplasts of Vicia faba L. : Evidence from Radiolabel Experiments. , 1988, Plant physiology.

[30]  R. Hedrich,et al.  Osmotic stress induces inactivation of photosynthesis in guard cell protoplasts of Vicia leaves. , 2001, Plant & cell physiology.

[31]  E. Zeiger,et al.  Light quality and osmoregulation in vicia guard cells : evidence for involvement of three metabolic pathways. , 1988, Plant physiology.

[32]  W. H. Outlaw.  Critical examination of the quantitative evidence for and against photosynthetic CO2 fixation by guard cells , 1989 .

[33]  T. Kinoshita,et al.  Guard-cell chloroplasts provide ATP required for H(+) pumping in the plasma membrane and stomatal opening. , 2001, Plant & cell physiology.

[34]  D. Lawlor.  Carbon and nitrogen assimilation in relation to yield: mechanisms are the key to understanding production systems. , 2002, Journal of experimental botany.

[35]  Tracy Lawson,et al.  Responses of photosynthetic electron transport in stomatal guard cells and mesophyll cells in intact leaves to light, CO2, and humidity. , 2002, Plant physiology.

[36]  M. Quiñones,et al.  Abaxial and adaxial stomata from Pima cotton (Gossypium barbadense L.) differ in their pigment content and sensitivity to light quality , 1993 .

[37]  J. Morison.  Stomatal response to increased CO2 concentration , 1998 .

[38]  A. S. Raghavendra.  Photosynthesis: A Comprehensive Treatise , 2000 .

[39]  A. Travis,et al.  Light Saturation of Stomatal Opening on the Adaxial and Abaxial Epidermis of Commelina communis , 1981 .

[40]  K. Shimazaki,et al.  Cyclic and Noncyclic Photophosphorylation in Isolated Guard Cell Chloroplasts from Vicia faba L. , 1985, Plant physiology.

[41]  J. Morison,et al.  Stomatal acclimation to increased CO2 concentration in a Florida scrub oak species Quercus myrtifolia Willd , 2001 .