Is nitrogen source the key for overcoming photosynthetic acclimation in Arabidopsis plants exposed to elevated CO2?

Trabajo presentado en el XIII Congreso Hispano-Luso de Fisiología Vegetal, celebrado en Oeiras (Portugal) en julio de 2013.Although the current [CO 2 ] in the atmosphere is generally limiting for C available information suggests that the predicted [ CO 2 ] increase will enhance rates in plants. However, it has been previously (B loom 2010, Stitt Krapp 1999) observed that responsiveness of plants to elevated [CO 2 ] will me mediated by its interaction with other li miting environmental factors, such as nitrogen availabilit y. According to those studies, N availability might decrease or eliminate the positive effect of elevated CO 2 on photosynthetic rates and consequently plant growth. The ‘capacity’ to adjust photosynthetic activity with plant C requirements has been described as a key process co nditioning photosynthetic performance under elevated [CO 2 ]. From this point of view, the reduction in photos ynthetic rates would be conditioned by a plant’s ability to develop new sin ks, or to expand the storage capacity or rate of existing sinks. According to Bloom et al . (2010), photosynthetic down might be conditioned by nitrate reductase activity and the inhibition of NO nt decline in plant N compounds. Furthermore, accor ding to those authors, the kind of nitrogen form applied to plants has a key role in r esponsiveness of plants to elevated [CO order to test the relevancy of N fertilization form in photosynthetic performance under elevated ] conditions, Arabidopsis thaliana (Columbia 0), grown hydroponically were exposed to ambient versus elevated [CO 2 ] concentrations (380 and 800 ppm respectively). Tw o different N forms were supplied at 0.75 mM, KNO 3 and NH 4 NO 3 . The plants were grown in a growth chamber (Hereaus Vötsch HPS 1500) at 16/8h (d/n) ph otoperiod, 22/18ºC (d/n) thermoperiod, 80% rH, 200 μmol photons m -2 s -1 PPDF, during 8 weeks (prior to flowering). Our resu lts revealed that Arabiopsis responsiveness to N fertili zation form was larger than that to elevated ], being the plants fertilized with NH 4 NO 3 and [CO 2 ] the ones with the largest biomass production and photosynthetic rates. More specifica lly, in NO 3 fed plants exposure to 800 ppm had significant effect in net photosynthesis (A N ) and electron transport rate (ETR), but Rubisco maximum carboxylation rate (Vc max ) and electron transport rate contributing to RuBP regeneration (J max ) had no significative effect. Furthermore, in thos e plants Rubisco and tot soluble protein (TSP) content was depleted by 35 an d 25 % respectively. In the other hand, A , J max such parameters were stimulated in NH 4 NO 3 fed plants. The larger responsiveness of photosynthetic apparatus observed in ammonium nitrate feed plants at 800 ppm was explained by their capacity to maintain con trol Rubisco and TSP content values. Those results remark the crucial influence of N sou rce on photosynthesis and its implications on protein metabolism of Arabidopsis plants grown in elevated CO 2.This study was supported in part by the the Spanish National Research and Development Programme (AGL2009-13339-C02-02) and AGL2011-30386-CO2-O2). Ivan Jauregui was the recipient of a FPI grant whereas Iker Aranjuelo was the recipient of a Ramón y Cajal research grant (Economy and Competitiveness Ministry).Peer Reviewe