Plant Cell Rep (2007) 26:133–143 DOI 10.1007/s00299-006-0221-7 CELL BIOLOGY AND MORPHOGENESIS Improved somatic embryo maturation in loblolly pine by monitoring ABA-responsive gene expression Teresa Vales · Xiaorong Feng · Lin Ge · Nanfei Xu · John Cairney · Gerald S. Pullman · Gary F. Peter Received: 14 February 2006 / Revised: 20 June 2006 / Accepted: 19 July 2006 / Published online: 29 August 2006 C  Springer-Verlag 2006 Abstract During loblolly pine zygotic embryo devel- opment, increases in mRNAs for three ABA-responsive LEA-like genes coincided with the two developmental stage-specific peaks of endogenous ABA accumulation (Kapik et al. 1995). These ABA concentration profiles from zygotic embryo development were used to develop several tissue culture approaches that altered the exposure of somatic embryos to exogenous ABA. Elevating exogenous ABA at a time corresponding to mid-maturation improved the germination and resulted in more zygotic-like expression of selected genes in somatic embryos. Extending the time on maturation medium for a fourth month increased embryo yield, dry weight, and germination in high-and low-yield Communicated by S. A. Merkle T. Vales · X. Feng · L. Ge · N. Xu · J. Cairney · G. S. Pullman Institute of Paper Science and Technology, 500 10th Street, NW Atlanta, GA 30318-5794, USA Present address: T. Vales Arborgen, P.O. Box 840001, Summerville, SC 29484, USA X. Feng Argos Therapeutics, 4233 Technology Drive, Durham, NC 27704, USA N. Xu BASF Plant Science, NC, 26 Davis Drive, RTP, NC 27709, USA G. F. Peter () School of Forest Resources and Conservation, University of Florida, P.O. Box 110410, Gainesville, FL 32611-0410, USA e-mail: gfpeter@ufl.edu genotypes. Optimizing the amounts of embryogenic suspen- sion, plated and exogenous ABA concentration increased from 22 to 66% in the early-stage bipolar embryos that developed to the cotyledonary stage. Keywords Somatic embryogenesis . Cell density . Abscisic acid . Loblolly pine . Gene expression Introduction The United States demand for wood, pulp, and paper prod- ucts is increasing, while forestlands available for timber harvesting and planting are decreasing due to urbanization, conservation, and land usage restrictions. To meet future de- mands for wood products from a reduced land base, research on planting and cultivation methods, traditional breeding, and intensive land management must function together to in- crease wood yields. The gains made from traditional breed- ing practices are now being enhanced through the develop- ment and application of clonal forestry practices, including the use of in vitro tissue culture methods (Libby and Rauter 1984; Park 2002). Tissue culture methods enable the rapid capture of high-value trees from breeding populations, pro- vide methods for long-term storage of elite germplasm, and facilitate propagation of large numbers of genetically uni- form stock for planting (Sutton 2002). Somatic embryogenesis has been used with many conifer species, including loblolly pine (Pinus taeda), to produce somatic embryos with the ability to germinate and form seedlings (Attree and Fowke 1993; Tautorus et al. 1991; Stasolla and Yeung 2003). However, Pinus species, including Pinus taeda, are often more recalcitrant toward somatic embryogenesis tissue culture methods (Becwar and Pullman 1995). The plant growth regulator, abscisic acid (ABA), plays a vital role in promoting maturation in Springer