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7 páginas, 2 figuras. ; Physical CO2 diffusion from sub-stomatal cavities to the chloroplasts where photosynthesis takes place is an important limitation of photosynthesis largely neglected in research related to global climate change. This limitation is particularly important in leaves with robust structures such as evergreen sclerophylls. In these leaves, photosynthesis is less sensitive to changes in stomatal openness, which is considered to be the primary limitation of photosynthesis. In this review we state that, because of large limitations in internal diffusion in C3 plants, photosynthesis and the intrinsic efficiency of the use of plant water responds more strongly to elevated levels of CO2 in leaves with more robust structures. This provides an additional explanation for the current apparent expansion of evergreen sclerophylls in many Earth ecosystems, and adds a new perspective to research of the biological effects of increasing atmospheric CO2. ; This study was supported by the Estonian Ministry of Science and Education (grant number SF1090065s07), a collaborative project between the Estonian Academy of Sciences and the Spanish CSIC, the Spanish Government (CGL2006-04025/BOS, CGL2010-17172/BOS and Consolider-Ingenio Montes CSD2008-00040), the CSIC grant PIF08- 006-3 and the Catalan Government grant SGR 2009-458. Research by JF was financed by the Spanish Ministry of Education and Research (Project BFU2008-1072-E/BFI). ; Peer reviewed

Flexas, Jaume et al.-- 14 páginas, 9 figuras, 157 referencias.-- cmartin@irnase.csic.es ; Mesophyll diffusion conductance to CO 2 is a key photosynthetic trait that has been studied intensively in the past years. The intention of the present review is to update knowledge of g m, and highlight the important unknown and controversial aspects that require future work. The photosynthetic limitation imposed by mesophyll conductance is large, and under certain conditions can be the most significant photosynthetic limitation. New evidence shows that anatomical traits, such as cell wall thickness and chloroplast distribution are amongst the stronger determinants of mesophyll conductance, although rapid variations in response to environmental changes might be regulated by other factors such as aquaporin conductance.Gaps in knowledge that should be research priorities for the near future include: how different is mesophyll conductance among phylogenetically distant groups and how has it evolved? Can mesophyll conductance be uncoupled from regulation of the water path? What are the main drivers of mesophyll conductance? The need for mechanistic and phenomenological models of mesophyll conductance and its incorporation in process-based photosynthesis models is also highlighted. ; The study was financially supported by the Estonian Ministry of Science and Education (grant SF1090065s07), the Spanish Ministry of Science and Innovation through projects BFU2008-01072 (MEFORE), AGL2009-11310/AGR, BFU2011-23294 (MECOME) and CGL2009- 13079-C02-01 (PALEOISOTREE), and the European Commission through European Regional Fund (the Estonian Center of Excellence in Environmental Adaptation), and the Marie Curie project MCERG- 246725 (FP7). J.P.F. is supported by the Ramón y Cajal program (RYC-2008-02050). A.G. had a Swiss National Science Fellowship (PA00P3 126259). M.M.B. and C.R.W are supported by Future Fellowships from the Australian Research Council (FT0992063 and FT100100024). C.D. was supported by a grant from the French government and by the cooperation project Tranzfor (Transferring Research between EU and Australia–New Zealand on Forestry and Climate Change, PIRSES-GA-2008-230793) funded by the European Union. ; Peer Reviewed

Background: Plant acclimation is a highly complex process, which cannot be fully understood by analysis at any one specific level (i.e. subcellular, cellular or whole plant scale). Various soft-computing techniques, such as neural networks or fuzzy logic, were designed to analyze complex multivariate data sets and might be used to model large such multiscale data sets in plant biology. Methodology and Principal Findings: In this study we assessed the effectiveness of applying neuro-fuzzy logic to modeling the effects of light intensities and sucrose content/concentration in the in vitro culture of kiwifruit on plant acclimation, by modeling multivariate data from 14 parameters at different biological scales of organization. The model provides insights through application of 14 sets of straightforward rules and indicates that plants with lower stomatal aperture areas and higher photoinhibition and photoprotective status score best for acclimation. The model suggests the best condition for obtaining higher quality acclimatized plantlets is the combination of 2.3% sucrose and photonflux of 122-130 μmol m-2 s -1. Conclusions: Our results demonstrate that artificial intelligence models are not only successful in identifying complex nonlinear interactions among variables, by integrating large-scale data sets from different levels of biological organization in a holistic plant systems-biology approach, but can also be used successfully for inferring new results without further experimental work. © 2014 Gago et al. ; This work was supported by The Regional Government Xunta de Galicia (PGIDIT02BTF30102PR) and Spanish MEC (AGL 2003-05877) to PPG. ML (PR2010-0460) and PPG (PR2010-0357) thank the Spanish Ministry of Education for their financial support during their sabbatical year at Faculty of Science, University of Utrecht, Netherlands ; Peer Reviewed

The alternative oxidase pathway (AOP) is associated with excess energy dissipation in leaves of terrestrial plants. To address whether this association is less important in palustrine plants, we compared the role of AOP in balancing energy and carbon metabolism in palustrine and terrestrial environments by identifying metabolic relationships between primary carbon metabolites and AOP in each habitat. We measured oxygen isotope discrimination during respiration, gas exchange, and metabolite profiles in aerial leaves of ten fern and angiosperm species belonging to five families organized as pairs of palustrine and terrestrial species. We performed a partial least square model combined with variable importance for projection to reveal relationships between the electron partitioning to the AOP (τa) and metabolite levels. Terrestrial plants showed higher values of net photosynthesis (AN) and τa, together with stronger metabolic relationships between τa and sugars, important for water conservation. Palustrine plants showed relationships between τa and metabolites related to the shikimate pathway and the GABA shunt, to be important for heterophylly. Excess energy dissipation via AOX is less crucial in palustrine environments than on land. The basis of this difference resides in the contrasting photosynthetic performance observed in each environment, thus reinforcing the importance of AOP for photosynthesis. ; This work was mainly supported by Ministerio de Economía y Competitividad (MINECO, Spain) (project PGC2018-093824-B-C41) and the ERDF (FEDER). Others funding were provided by FONDECYT No. 1191118 from National Agency for Research and Development (ANID) and the Chilean Scholarship Program/Becas de doctorado nacional/2017–21180329, the European Union's Horizon 2020 Research and Innovation Program under the Marie Skłodowska-Curie grant agreement no. 753301, the 'Ramon y Cajal' contract RYC2019-027244-I/AEI/10.13039/501100011033 and the European Social Fund. ; Peer reviewed

Mesophyll diffusion conductance to CO 2 is a key photosynthetic trait that has been studied intensively in the past years. The intention of the present review is to update knowledge of g m, and highlight the important unknown and controversial aspects that require future work. The photosynthetic limitation imposed by mesophyll conductance is large, and under certain conditions can be the most significant photosynthetic limitation. New evidence shows that anatomical traits, such as cell wall thickness and chloroplast distribution are amongst the stronger determinants of mesophyll conductance, although rapid variations in response to environmental changes might be regulated by other factors such as aquaporin conductance.Gaps in knowledge that should be research priorities for the near future include: how different is mesophyll conductance among phylogenetically distant groups and how has it evolved? Can mesophyll conductance be uncoupled from regulation of the water path? What are the main drivers of mesophyll conductance? The need for mechanistic and phenomenological models of mesophyll conductance and its incorporation in process-based photosynthesis models is also highlighted. ; The study was financially supported by the Estonian Ministry of Science and Education (grant SF1090065s07), the Spanish Ministry of Science and Innovation through projects BFU2008-01072 (MEFORE), AGL2009-11310/AGR, BFU2011-23294 (MECOME) and CGL2009-13079-C02-01 (PALEOISOTREE), and the European Commission through European Regional Fund (the Estonian Center of Excellence in Environmental Adaptation), and the Marie Curie project MC-ERG-246725 (FP7). J.P.F. is supported by the Ramón y Cajal program (RYC-2008-02050). A.G. had a Swiss National Science Fellowship (PA00P3_126259). M.M.B. and C.R.W are supported by Future Fellowships from the Australian Research Council (FT0992063 and FT100100024). C.D. was supported by a grant from the French government and by the cooperation project Tranzfor (Transferring Research between EU and Australia–New Zealand on Forestry and Climate Change, PIRSES-GA-2008-230793) funded by the European Union.