Planta (2008) 227:1063–1077 DOI 10.1007/s00425-007-0681-1 123 ORIGINAL ARTICLE Carbohydrate mobilization and gene regulatory proWle in the pseudobulb of Oncidium orchid during the Xowering process Chih-Yu Wang · Chung-Yi Chiou · Heng-Long Wang · Ramanarayan Krishnamurthy · Shripathi Venkatagiri · Jun Tan · Kai-Wun Yeh Received: 16 October 2007 / Accepted: 7 December 2007 / Published online: 9 January 2008  Springer-Verlag 2007 Abstract The pseudobulb of Oncidium orchid is a storage organ for supplying water, minerals and carbohydrates to the developing inXorescence. DiVerent patterns of mannan, starch and pectin metabolism were observed in the pseudo- bulb of three developmental stages by histochemical stain- ing and high performance anion exchange chromatographic (HPAEC) analysis. Copious pectin was strongly stained by ruthenium red in young pseudobulbs demonstrating that mannan and pectin were preferentially accumulated in the young pseudobulb sink at inXorescence pre-initiation stage. Concomitant with the emergence of the inXorescence, man- nan and pectin decreased gradually and converted to starch. The starch, synthesized at the inXorescence developing stage, was eventually degraded at the Xoral development stage. A systematic survey on the subtractive EST (expres- sion sequence tag) library of pseudobulb in the inXores- cence pre-initiation stage revealed the presence of Wve groups of gene homologues related to sucrose, mannan, starch, pectin and other carbohydrate metabolism. The tran- scriptional level of 13 relevant genes related to carbohy- drate metabolism was characterized from pseudobulbs of three diVerent developmental stages. The speciWc activities of the enzymes encoded by these genes were also assayed. The expression proWles of these genes show that the tran- scriptional levels largely correlated with the enzyme activi- ties, which were associated with the respective carbohydrate pools. These results demonstrated a novel functional proWle of polysaccharide mobilization pathway as well as their relevant gene expression in the pseudobulb of Oncidium orchid during the Xowering process. Keywords Carbohydrate metabolism · EST (expressed sequence tags) · InXorescence · Oncidium · Pseudobulb Abbreviations HPAEC High performance anion exchange chromatography EST Expression sequence tags Introduction Carbohydrates are important nutritients and energy sources in living organisms. The structural components of the cells are largely made up of carbohydrates. During plant growth and development, photoassimilates produced by the source leaf are translocated toward diVerent sinks for utilization or accumulation. The source leaves accumulate large foliar carbohydrate pools to buVer variations in the rate of photo- synthesis and to liberate suYcient sucrose at night to ensure a more or less continuous supply of sucrose for sink organs in many plant species (Geiger 1987). Recent evidence has C.-Y. Wang · C.-Y. Chiou · R. Krishnamurthy · J. Tan · K.-W. Yeh (&) Institute of Plant Biology, National Taiwan University, Taipei, 106, Taiwan e-mail: ykwbppp@ntu.edu.tw H.-L. Wang Department of Life Science, National University of Kaohsiung, Kaohsiung, Taiwan J. Tan College of Bioinformatics, Chongqing University of Posts and Telecommunications, Chongqing 400065, China Present Address: S. Venkatagiri Department of Botany, Karnatak University, Dharwad, India