SummaryLeaf 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 .

La disponibilidad de agua es el principal factor limitante de la producción agrícola y ganadera en ambientes de clima mediterráneo. Limitación que, ante las previsiones de Cambio Climático Global realizadas por organismo internacionales, serán mucho mayores en los próximos años. En este escenario, la efi ciencia en el uso de los recursos hídricos debe ser un aspecto transversal de las políticas públicas que debe, por tanto, ser afrontado desde diversos puntos de vista. En este sentido, uno de los temas claves a considerar es la efi ciencia con la que las plantas usan el agua. El objetivo de este trabajo es hacer una revisión de los diferentes aspectos relacionados con este tema, considerando las diferentes escalas a las que se estudia la efi ciencia en el uso del agua por las plantas (EUA), desde la hoja hasta el cultivo o el ecosistema. Así, se abordan las difi cultades técnicas que existen para medir, de una forma precisa, la EUA de un cultivo o de un ecosistema, la importancia del ambiente y de las prácticas agronómicas como determinantes de la EUA, la diversidad genética inter e intraespecífi ca, y las implicaciones prácticas de estos factores a la hora de incrementar la EUA.

<p style="text-align: justify;"><strong>Aims</strong>: The use of healthy propagating material is required to control grapevine viruses. The aim of this work was to eliminate <em>Grapevine fleck virus</em> (GFkV) from a Manto Negro clone, a local grapevine variety, in order to include this material in certification programs. Additionally, the effects of virus elimination on photosynthesis and related parameters were evaluated.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Two method combinations for virus elimination were evaluated: (1) field thermotherapy and shoot tip culture and (2) chamber thermotherapy and shoot tip culture. GFkV elimination was tested by double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) and reverse transcription-polymerase chain reaction (RT-PCR). The results suggest that a natural field thermotherapy prior to shoot tip culture is effective, making unnecessary the chamber thermotherapy treatment. Additionally, the effects of virus elimination on gas exchanges, chlorophyll fluorescence, electron transport rate (ETR), protein and pigment content were evaluated. The results indicate that GFkV infection affects physiological processes, especially stomatal conductance (g_s), whereas photosynthesis, protein, pigment content, ETR, and fluorescence parameters were not significantly changed. </p><p style="text-align: justify;"><strong>Conclusion</strong>: This study described a simple and rapid method that requires only one medium for virus elimination (GFkV). Beyond its sanitation potential, the use of larger explants (1-3 mm) ensures the integrity of the clone. The presence of the virus affects physiological processes, especially g_s, demonstrating the beneficial effect of eliminating GFkV. <strong></strong></p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: The described method has the potential to produce GFkV-free rooted plantlets faster than other methods while being potentially safer in maintaining the genetic and phenotypic stability of the regenerated clone. The beneficial effects of GFkV elimination provide evidence for the importance to detect this virus prior to the inclusion of clones in certification programs.</p>

Background and Aims Measuring the carbon assimilation and respiration during vine phenology can provide an understanding of the dynamics of carbon fluxes from different organs and their relationship. Most field studies to date do not consider the respiratory losses of different plant organs and their variability under environmental, genetic and phenological changes. The aim of this study was to investigate the effect of genotype and water regime on carbon assimilation, respiration and allocation during vine phenology. Methods and Results Field trials were carried out during 2013 and 2014 to study the effect of genotype and water status on carbon assimilation, respiratory losses from leaves, shoots, fruits and roots during the vine phenological cycle, and on biomass production. Carbon respiration varied during plant phenology and represented a significant proportion of the total vine carbon assimilation. The integrated carbon respiratory loss in leaves, fruits and roots was greater in irrigated vines than in non‐irrigated vines. Tempranillo recorded the highest carbon assimilation, leaf and stem respiration, as well as the highest above‐ground biomass. Garnacha showed a higher root respiration loss and allocated more biomass to the permanent organs. Accumulation of above‐ground biomass was influenced by plant carbon budgets during the growing season. Conclusions Vine phenology, cultivar and plant water status affected carbon assimilation, carbon loss and carbon allocation. Non‐irrigated vines had a higher respiratory carbon loss in respect to the total carbon assimilation by photosynthesis. Above‐ and below‐ground carbon fluxes were coupled during vine phenology. Significance of the Study The present work illustrates the importance of respiratory processes on the carbon balance and the relationship among different carbon balance components during vine phenology.

Based on a previous work, exposure to limited water availability induced changes in cell wall composition of mature Helianthus annuus L. leaves that affected mesophyll conductance to CO2 diffusion (gm). However, it is unclear on which timescale these cell wall composition changes occur. Here, we tested H. annuus subjected to control (i.e., water availability), different levels of short-term water deficit stress (ST), long-term water deficit stress (LT) and long-term water deficit stress followed by gradual recoveries addressed at different timescales (LT-Rec) to evaluate the dynamics of modifications in cell wall main composition (cellulose, hemicelluloses, pectins and lignins) affecting photosynthesis. During gradual ST treatments, pectins enhancements were associated with gm declines. However, during LT-Rec, pectins content decreased significantly after only 5 h, while hemicelluloses and lignins amounts changed after 24 h, all of them being uncoupled from gm. Surprisingly, lignins increased by around 200% as compared to control and were related to stomatal conductance to gas diffusion (gs) during LT-Rec. Although we suspect that the accuracy of the protocols to determine cell wall composition should be re-evaluated, we demonstrate for the first time that a highly dynamic cell wall composition turnover differently affects photosynthesis in plants subjected to distinct water regimes.