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Liquid Culture Systems for in vitro Plant Propagation

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Chapter 20<br />

<strong>Propagation</strong> of Norway spruce via somatic embryogenesis<br />

Sara von Arnold 1 , Peter Bozhkov, David Clapham, Julia Dyachok, Lada<br />

Filonova, Karl-Anders Högberg 2 , Mathieu Ingouff & Malgorzata Wiweger<br />

1 Department of Forest Genetics, SLU, PO Box 7027, S-750 07 Uppsala, Sweden.<br />

Phone: +46 18 673230, Fax: +46 18 6732, E-mail: Sara.von.Arnold@sgen.slu.se<br />

2 The Forestry Research Institute of Sweden, Ekebo, S-268 90 Svalöv, Sweden.<br />

Abstract: Somatic embryogenesis comb<strong>in</strong>ed with cryopreservation is an attractive method to<br />

propagate Norway spruce (Picea abies) vegetatively both as a tool <strong>in</strong> the breed<strong>in</strong>g programme<br />

and <strong>for</strong> large-scale clonal propagation of elite material. Somatic embryos are also a valuable<br />

tool <strong>for</strong> study<strong>in</strong>g regulation of embryo development. Embryogenic cell l<strong>in</strong>es of Norway<br />

spruce are established from zygotic embryos. The cell l<strong>in</strong>es proliferate as proembryogenic<br />

masses (PEMs). Somatic embryos develop from PEMs. PEM-to-somatic embryo transition is<br />

a key developmental switch that determ<strong>in</strong>es the yield and quality of mature somatic embryos.<br />

Withdrawal of plant growth regulators stimulates PEM-to-somatic embryo transition<br />

accompanied by programmed cell death (PCD) <strong>in</strong> PEMs. This PCD is mediated by a marked<br />

decrease <strong>in</strong> extracellular pH. If the acidification is abolished by buffer<strong>in</strong>g the culture medium,<br />

PEM-to-somatic embryo transition together with PCD is <strong>in</strong>hibited. Cell death, <strong>in</strong>duced by<br />

withdrawal of PGRs, can be suppressed by extra supply of lipo-chitooligosaccharides (LCOs).<br />

Extracellular chit<strong>in</strong>ases are probably <strong>in</strong>volved <strong>in</strong> production and degradation of LCOs. Dur<strong>in</strong>g<br />

early embryogeny, the embryos <strong>for</strong>m an embryonal mass surrounded by a surface layer. The<br />

<strong>for</strong>mation of a surface layer is accompanied by a switch <strong>in</strong> the expression pattern of an Ltplike<br />

gene (Pa18) and a homeobox gene (PaHB1), from ubiquitous expression <strong>in</strong> PEMs to<br />

surface layer-specific <strong>in</strong> somatic embryos. Ectopic expression of Pa18 and PaHB1 leads to an<br />

early developmental block. Transgenic embryos and plants of Norway spruce are rout<strong>in</strong>ely<br />

produced by us<strong>in</strong>g a biolistic approach. The transgenic material is used <strong>for</strong> study<strong>in</strong>g the<br />

importance of specific genes <strong>for</strong> regulat<strong>in</strong>g plant development, but transgenic plants can also<br />

be used <strong>for</strong> identification of candidate genes <strong>for</strong> use <strong>in</strong> the breed<strong>in</strong>g programme.<br />

Key words: condition<strong>in</strong>g factors, development of somatic embryos, embryogenic cell<br />

suspension, gene trans<strong>for</strong>mation, genetic regulation, Norway spruce, programmed cell death<br />

Abbreviations: ABA – abscisic acid; AGP – arab<strong>in</strong>ogalactan prote<strong>in</strong>; LCO – lipochitooligosaccharide;<br />

PCD – programmed cell death; PEM – proembryogenic mass;<br />

PGR – plant growth regulator<br />

283<br />

A.K. Hvoslef-Eide and W. Preil (eds.), <strong>Liquid</strong> <strong>Culture</strong> <strong>Systems</strong> <strong>for</strong> <strong>in</strong> <strong>vitro</strong> <strong>Plant</strong> <strong>Propagation</strong>, 283–293.<br />

© 2005 Spr<strong>in</strong>ger. Pr<strong>in</strong>ted <strong>in</strong> the Netherlands.

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