Physiologia Plantarum 2015 © 2015 Scandinavian Plant Physiology Society, ISSN 0031-9317 Distinct regulation in inflorescence carbohydrate metabolism according to grapevine cultivars during floral development Mélodie Sawicki, Lucile Jacquens, Fabienne Baillieul, Christophe Clément, Nathalie Vaillant-Gaveau † and Cédric Jacquard †,* Laboratoire de Stress, Défenses et Reproduction des Plantes, UPRES EA4707, Université de Reims Champagne-Ardenne, UFR Sciences, Reims, France Correspondence *Corresponding author, e-mail: cedric.jacquard@univ-reims.fr Received 27 October 2014; revised 8 December 2014 doi:10.1111/ppl.12321 Carbohydrate metabolism is important in plant sexual reproduction because sugar contents are determining factors for both flower initiation and flo- ral organ development. In woody plants, flowering represents the most energy-consuming step crucial to reproductive success. Nevertheless, in these species, the photosynthesis performed by flowers supplies the carbon required for reproduction. In grapevine (Vitis vinifera), the inflorescence has a specific status because this organ imports carbohydrates at the same time as it exports photoassimilates. In this study, fluctuations in carbohydrate metabolism were monitored by analyzing gas exchanges, photosynthetic electron transport capacity, carbohydrate contents and some activities of carbohydrate metabolism enzymes, in the inflorescences of Pinot noir and Gewurztraminer, two cultivars with a different sensitivity to coulure phe- nomenon. Our results showed that photosynthetic activity and carbohydrate metabolism are clearly different and differently regulated during the floral development in the two cultivars. Indeed, the regulation of the linear electron flow and the cyclic electron flow is not similar. Moreover, the regulation of PSII activity, with a higher Y(NPQ)/Y(NO) ratio in Gewurztraminer, can be correlated with the higher protection of the photosynthetic chain and consequently with the higher yield under optimal conditions of this cultivar. At least, our results showed a higher photosynthetic activity and a better protection of PSI in Pinot noir during the floral development. † Both authors contributed equally to this work. Abbreviations – A, alpha amylase;  A, beta amylase; APMSF, 4-Amidinophenylmethanesulfonyl fluoride hydrochloride; BBCH, Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie; CEF, cyclic electron flow; DMSO, Dimethyl- sulfoxid; DTT, Dithiothreitol; EGTA, Ethylen glycol-bis(2-aminoethylether)-N,N,N’,N’-tetraacetic acid; ETRI, rate of charge separation at photosystem I reaction centers; ETRII, rate of charge separation at photosystem II reaction centers; FM, female meiosis; FM+x, number of days following FM; FNR, ferredoxin-NADP + reductase; FW, fresh weight; GW, Gewurztraminer; HEPES, 4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid; LEF, linear electron flow; NPQ, non-photochemical quenching; PAR, photosynthetically active radiation; PC, plastocyanin; PCR, polymerase chain reaction; PEG, Polyethylene glycol; PN, Pinot noir; PSI, photosytem I; PSII, photosystem II; PVP, Polyvinylpyrrolidone; RuBisCO, Ribulose-1,5-bisphosphate carboxy- lase/oxygenase; SPS, sucrose phosphate synthase; SS, starch synthase; SSs, sucrose synthase; WB inv, cell wall apoplastic invertase; Y(I), effective photosystem I quantum yield; Y(II), effective photosystem II quantum yield; Y(II)/Y(I), contribution of LEF to Y(I); Y(NA), non-photochemical quantum yield of photosystem I due to acceptor side limitation; Y(ND), non-photochemical quantum yield of photosystem I due to donor side limitation; Y(NO), quantum yield of non-regulated energy dissipation in photosystem II; Y(NPQ), quantum yield of regulated energy dissipation in photosystem II. Physiol. Plant. 2015