Tobacco aquaporin NtAQP1 is involved in mesophyll conductance to CO2 in vivo.

Leaf mesophyll conductance to CO(2) (g(m)) has been recognized to be finite and variable, rapidly adapting to environmental conditions. The physiological basis for fast changes in g(m) is poorly understood, but current reports suggest the involvement of protein-facilitated CO(2) diffusion across cell membranes. A good candidate for this could be the Nicotiana tabacum L. aquaporin NtAQP1, which was shown to increase membrane permeability to CO(2) in Xenopus oocytes. The objective of the present work was to evaluate its effect on the in vivo mesophyll conductance to CO(2), using plants either deficient in or overexpressing NtAQP1. Antisense plants deficient in NtAQP1 (AS) and NtAQP1 overexpressing tobacco plants (O) were compared with their respective wild-type (WT) genotypes (CAS and CO). Plants grown under optimum conditions showed different photosynthetic rates at saturating light, with a decrease of 13% in AS and an increase of 20% in O, compared with their respective controls. CO(2) response curves of photosynthesis also showed significant differences among genotypes. However, in vitro analysis demonstrated that these differences could not be attributed to alterations in Rubisco activity or ribulose-1,5-bisphosphate content. Analyses of chlorophyll fluorescence and on-line (13)C discrimination indicated that the observed differences in net photosynthesis (A(N)) among genotypes were due to different leaf mesophyll conductances to CO(2), which was estimated to be 30% lower in AS and 20% higher in O compared with their respective WT. These results provide evidence for the in vivo involvement of aquaporin NtAQP1 in mesophyll conductance to CO(2).

[1]  X. Le Roux,et al.  Effect of local irradiance on CO(2) transfer conductance of mesophyll in walnut. , 2002, Journal of experimental botany.

[2]  E. Singsaas,et al.  Elevated CO2 effects on mesophyll conductance and its consequences for interpreting photosynthetic physiology , 2004 .

[3]  F. Loreto,et al.  The use of low [CO2] to estimate diffusional and non‐diffusional limitations of photosynthetic capacity of salt‐stressed olive saplings , 2003 .

[4]  R. Valentini,et al.  In situ estimation of net CO2 assimilation, photosynthetic electron flow and photorespiration in Turkey oak (Q. cerris L.) leaves: diurnal cycles under different levels of water supply , 1995 .

[5]  M. Adams,et al.  Internal conductance does not scale with photosynthetic capacity: implications for carbon isotope discrimination and the economics of water and nitrogen use in photosynthesis. , 2006, Plant, cell & environment.

[6]  D. Manter,et al.  A/C(i) curve analysis across a range of woody plant species: influence of regression analysis parameters and mesophyll conductance. , 2004, Journal of experimental botany.

[7]  U. Zimmermann,et al.  Significance of plasmalemma aquaporins for water-transport in Arabidopsis thaliana. , 1998, The Plant journal : for cell and molecular biology.

[8]  T. Zeuthen,et al.  Aquaporin 6 is permeable to glycerol and urea , 2004, Pflügers Archiv.

[9]  C. Maurel,et al.  The vacuolar membrane protein gamma‐TIP creates water specific channels in Xenopus oocytes. , 1993, The EMBO journal.

[10]  W. Boron,et al.  Effect of PCMBS on CO2permeability of Xenopus oocytes expressing aquaporin 1 or its C189S mutant. , 1998, American journal of physiology. Cell physiology.

[11]  A. Kaplan,et al.  Nature of the rate-limiting step in the supply of inorganic carbon for photosynthesis in isolated asparagus mesophyll cells. , 1983, Plant physiology.

[12]  D. Luu,et al.  Cytosolic pH regulates root water transport during anoxic stress through gating of aquaporins , 2003, Nature.

[13]  Nigel J. Livingston,et al.  On the need to incorporate sensitivity to CO2 transfer conductance into the Farquhar–von Caemmerer–Berry leaf photosynthesis model , 2004 .

[14]  John R. Evans,et al.  Determination of the Average Partial Pressure of CO2 in Chloroplasts From Leaves of Several C3 Plants , 1991 .

[15]  S. Long,et al.  Gas exchange measurements, what can they tell us about the underlying limitations to photosynthesis? Procedures and sources of error. , 2003, Journal of experimental botany.

[16]  Effects of low CO2 on NAD(P)H dehydrogenase, a mediator of cyclic electron transport around photosystem I in the cyanobacterium synechocystis PCC6803. , 2003, Plant & cell physiology.

[17]  G. Farquhar,et al.  Low conductances for CO2 diffusion from stomata to the sites of carboxylation in leaves of woody species , 1992 .

[18]  J. R. Evans,et al.  The Relationship Between CO2 Transfer Conductance and Leaf Anatomy in Transgenic Tobacco With a Reduced Content of Rubisco , 1994 .

[19]  C. Maurel,et al.  Chapter 7 Aquaporins of plants: Structure, function, regulation, and role in plant water relations , 2001 .

[20]  R. Hedrich,et al.  The Nicotiana tabacum plasma membrane aquaporin NtAQP1 is mercury-insensitive and permeable for glycerol. , 1999, The Plant journal : for cell and molecular biology.

[21]  T. Sharkey,et al.  Measurements of mesophyll conductance, photosynthetic electron transport and alternative electron sinks of field grown wheat leaves , 1994, Photosynthesis Research.

[22]  A. Mas,et al.  Plant aquaporins. , 2002, Physiologia plantarum.

[23]  U. Sonnewald,et al.  High CO2‐mediated down‐regulation of photosynthetic gene transcripts is caused by accelerated leaf senescence rather than sugar accumulation , 2000, FEBS letters.

[24]  F. Loreto,et al.  Acquisition and Diffusion of CO2 in Higher Plant Leaves , 2000 .

[25]  F. Loreto,et al.  Photosynthetic limitations in olive cultivars with different sensitivity to salt stress , 2003 .

[26]  T. Zeuthen,et al.  Bidirectional Water Fluxes and Specificity for Small Hydrophilic Molecules in Aquaporins 0–5* , 1998, The Journal of Biological Chemistry.

[27]  S. Long,et al.  Respiratory Oxygen Uptake Is Not Decreased by an Instantaneous Elevation of [CO2], But Is Increased with Long-Term Growth in the Field at Elevated [CO2]1 , 2004, Plant Physiology.

[28]  G. Farquhar,et al.  Effect of temperature on the CO2/O2 specificity of ribulose-1,5-bisphosphate carboxylase/oxygenase and the rate of respiration in the light , 1985, Planta.

[29]  O. Roupsard,et al.  Limitation of photosynthetic activity by CO2 availability in the chloroplasts of oak leaves from different species and during drought , 1996 .

[30]  I. Terashima,et al.  Effects of HgCl(2) on CO(2) dependence of leaf photosynthesis: evidence indicating involvement of aquaporins in CO(2) diffusion across the plasma membrane. , 2002, Plant & cell physiology.

[31]  J. R. Coleman,et al.  Photosynthetic Gas Exchange and Discrimination against 13CO2 and C18O16O in Tobacco Plants Modified by an Antisense Construct to Have Low Chloroplastic Carbonic Anhydrase , 1996, Plant physiology.

[32]  R. Kaldenhoff,et al.  New aspects of plant aquaporin regulation and specificity , 1999 .

[33]  Larsson,et al.  Aquaporins and water homeostasis in plants. , 1999, Trends in plant science.

[34]  Thomas D. Sharkey,et al.  Photometric method for routine determination of kcat and carbamylation of rubisco , 1991, Photosynthesis Research.

[35]  I. Terashima,et al.  Effects of leaf age on internal CO2 transfer conductance and photosynthesis in tree species having different types of shoot phenology , 2001 .

[36]  E. Steudle,et al.  A cohesion/tension mechanism explains the gating of water channels (aquaporins) in Chara internodes by high concentration. , 2004, Journal of experimental botany.

[37]  I. Terashima,et al.  Overexpression of the barley aquaporin HvPIP2;1 increases internal CO(2) conductance and CO(2) assimilation in the leaves of transgenic rice plants. , 2004, Plant & cell physiology.

[38]  G. Farquhar,et al.  On the relationship between leaf anatomy and CO2 diffusion through the mesophyll of hypostomatous leaves , 1995 .

[39]  J. Briantais,et al.  The relationship between the quantum yield of photosynthetic electron transport and quenching of chlorophyll fluorescence , 1989 .

[40]  M. Tyree,et al.  PIP1 plasma membrane aquaporins in tobacco: from cellular effects to function in plants. , 2002, The Plant cell.

[41]  T. Sharkey,et al.  Estimation of Mesophyll Conductance to CO(2) Flux by Three Different Methods. , 1992, Plant physiology.

[42]  C. Lovisolo,et al.  The tobacco aquaporin NtAQP1 is a membrane CO2 pore with physiological functions , 2003, Nature.

[43]  M. R. Badger,et al.  Specific reduction of chloroplast carbonic anhydrase activity by antisense RNA in transgenic tobacco plants has a minor effect on photosynthetic CO2 assimilation , 1994, Planta.

[44]  T. Andrews,et al.  Directed mutation of the Rubisco large subunit of tobacco influences photorespiration and growth. , 1999, Plant physiology.

[45]  Steven D. Sargent,et al.  Tunable diode laser absorption spectroscopy for stable isotope studies of ecosystem–atmosphere CO2 exchange , 2003 .

[46]  D. Epron,et al.  Limitation of net CO2 assimilation rate by internal resistances to CO2 transfer in the leaves of two tree species (Fagus sylvatica L. and Castanea sativa Mill.) , 1995 .

[47]  G. Galili,et al.  Overexpression of a Plasma Membrane Aquaporin in Transgenic Tobacco Improves Plant Vigor under Favorable Growth Conditions but Not under Drought or Salt Stress Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.009225. , 2003, The Plant Cell Online.

[48]  B. Osmond,et al.  Distinctive Responses of Ribulose-1,5-Bisphosphate Carboxylase and Carbonic Anhydrase in Wheat Leaves to Nitrogen Nutrition and their Possible Relationships to CO(2)-Transfer Resistance. , 1992, Plant physiology.

[49]  I. Terashima,et al.  Slow development of leaf photosynthesis in an evergreen broad‐leaved tree, Castanopsis sieboldii: relationships between leaf anatomical characteristics and photosynthetic rate , 2001 .

[50]  Thomas Zeuthen,et al.  Aquaporin homologues in plants and mammals transport ammonia , 2004, FEBS letters.

[51]  D. Wilkins,et al.  Regulation of the expression of photosynthetic nuclear genes by CO2 is mimicked by regulation by carbohydrates: a mechanism for the acclimation of photosynthesis to high CO2? , 1994 .

[52]  T. Sharkey,et al.  Theoretical Considerations when Estimating the Mesophyll Conductance to CO(2) Flux by Analysis of the Response of Photosynthesis to CO(2). , 1992, Plant physiology.

[53]  Binghua Wu,et al.  Point mutations in the aromatic/arginine region in aquaporin 1 allow passage of urea, glycerol, ammonia, and protons. , 2006, Proceedings of the National Academy of Sciences of the United States of America.

[54]  H. Sasaki,et al.  Analysis by δ13C Measurement on Mechanism of Cultivar Difference in Leaf Photosynthesis of Rice (Oryza sativa L.) , 1996 .

[55]  F. Loreto,et al.  Consequences of salt stress on conductance to CO2 diffusion, Rubisco characteristics and anatomy of spinach leaves , 1998 .

[56]  D. Yakir,et al.  Internal Conductance to CO2 Diffusion and C18OO Discrimination in C3 Leaves , 2000 .

[57]  R. Kaldenhoff,et al.  Cell-specific expression of the mercury-insensitive plasma-membrane aquaporin NtAQP1 from Nicotiana tabacum , 2000, Planta.

[58]  C. Maurel,et al.  A proteomic study reveals novel insights into the diversity of aquaporin forms expressed in the plasma membrane of plant roots. , 2003, The Biochemical journal.

[59]  J. Berry,et al.  A biochemical model of photosynthetic CO2 assimilation in leaves of C3 species , 1980, Planta.

[60]  Murray R. Badger,et al.  The interplay between limiting processes in C3 photosynthesis studied by rapid-response gas exchange using transgenic tobacco impaired in photosynthesis , 1998 .

[61]  F. Loreto,et al.  Gas-Exchange Properties of Salt-Stressed Olive (Olea europea L.) Leaves. , 1989, Plant physiology.

[62]  W. Frommer,et al.  Urea Transport by Nitrogen-Regulated Tonoplast Intrinsic Proteins in Arabidopsis1 , 2003, Plant Physiology.

[63]  Thomas D. Sharkey,et al.  An improved model of C3 photosynthesis at high CO2: Reversed O2 sensitivity explained by lack of glycerate reentry into the chloroplast , 1991, Photosynthesis Research.

[64]  Graham D. Farquhar,et al.  On the Relationship Between Carbon Isotope Discrimination and the Intercellular Carbon Dioxide Concentration in Leaves , 1982 .

[65]  F. Manes,et al.  Fluorescence Parameters Measured Concurrently with Net Photosynthesis to Investigate Chloroplastic CO2 Concentration in Leaves of Quercus ilex L. , 1990 .

[66]  Susanne von Caemmerer,et al.  Temperature Response of Mesophyll Conductance. Implications for the Determination of Rubisco Enzyme Kinetics and for Limitations to Photosynthesis in Vivo , 2002, Plant Physiology.

[67]  H. Sinoquet,et al.  Spatial distribution of leaf water‐use efficiency and carbon isotope discrimination within an isolated tree crown , 2001 .

[68]  C. Giménez,et al.  Regulation of Photosynthetic Rate of Two Sunflower Hybrids under Water Stress. , 1992, Plant physiology.

[69]  C. Maurel,et al.  Aquaporins. A molecular entry into plant water relations. , 2001, Plant physiology.

[70]  S. von Caemmerer,et al.  Carbon Dioxide Diffusion inside Leaves , 1996, Plant physiology.

[71]  Jaume Flexas,et al.  Effects of drought on photosynthesis in grapevines under field conditions: an evaluation of stomatal and mesophyll limitations. , 2002, Functional plant biology : FPB.

[72]  Villani,et al.  Restrictions to carbon dioxide conductance and photosynthesis in spinach leaves recovering from salt stress , 1999, Plant physiology.

[73]  C. Maurel,et al.  Purified vesicles of tobacco cell vacuolar and plasma membranes exhibit dramatically different water permeability and water channel activity. , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[74]  S. Tyerman,et al.  Plant aquaporins: multifunctional water and solute channels with expanding roles. , 2002, Plant, cell & environment.

[75]  M. Eckert.  Review article. New aspects of plant aquaporin regulation and specificity , 1999 .

[76]  T. Sharkey,et al.  Carbon isotope discrimination measured concurrently with gas exchange to investigate CO2 diffusion in leaves of higher plants , 1986 .

[77]  T. Sharkey,et al.  Diffusive and metabolic limitations to photosynthesis under drought and salinity in C(3) plants. , 2004, Plant biology.

[78]  H. Mi,et al.  Effects of low CO2 on NAD(P)H dehydrogenase, a mediator of cyclic electron transport around photosystem I in the cyanobacterium synechocystis PCC6803. , 2003, Plant & cell physiology.

[79]  T. Sharkey,et al.  Regulation of photosynthetic electron-transport in Phaseolus vulgaris L., as determined by room-temperature chlorophyll a fluorescence , 1988, Planta.

[80]  T. Sharkey,et al.  Activity ratios of ribulose-1,5-bisphosphate carboxylase accurately reflect carbamylation ratios. , 1989, Plant physiology.

[81]  Park S. Nobel,et al.  Physicochemical and Environmental Plant Physiology , 1991 .

[82]  H. Jones.  Physicochemical and Environmental Plant Physiology, 2nd edn. , 1999 .