Annals of Botany 90: 11-19, 2002
© 2002 Annals of Botany Company
Photoautotrophic Culture of Coffea arabusta Somatic Embryos: Photosynthetic Ability and Growth of Different Stage Embryos
,1,1,11 Department of Bioproduction Science, Chiba University, Matsudo, Chiba 271-8510, Japan
* For correspondence. Fax 00 1 519 7670755, e-mail: szobayed{at}uoguelph.ca Present address: Department of Plant Agriculture, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
Received: 17 December 2001; Returned for revision: 1 February 2002; Accepted: 19 March 2002
Coffea arabusta somatic embryos were cultured and development of stomata, rate of CO2 fixation or production, chlorophyll content and chlorophyll fluorescence were studied in embryos at different stages of development. Cotyledonary and germinated embryos have photosynthetic capacity, although pretreatment at a high photosynthetic photon flux (PPF) (100 µmol m–2 s–1) for 14 d increased photosynthetic ability. Except in a very small number of cases, stomata did not develop fully in precotyledonary stage embryos and were absent in torpedo stage embryos. Low chlorophyll content (90–130 µg g–1 fresh mass) was noted in torpedo and precotyledonary stage embryos compared with cotyledonary and germinated embryos (300–500 µg g–1 fresh mass). Due to the absence of stomata and low chlorophyll content in the torpedo and precotyledonary stage embryos, the photosynthetic rate was low and, in some cases, CO2 production was observed. These data suggest that the cotyledonary stage is the earliest stage that can be cultured photoautotrophically to ensure plantlet development. When grown photoautotrophically (in a sugar-free medium with CO2 enrichment in the culture headspace and high photosynthetic photon flux), torpedo and precotyledonary stage embryos lost 20–25 % of their initial dry mass after 60 d of culture. However, in cotyledonary and germinated embryos, the dry mass of each embryo increased by 10 and 50 %, respectively. By using a porous supporting material, growth (especially root growth) was increased in cotyledonary stage embryos. In addition, photoautotrophic conditions, high PPF (100–150 µmol m–2 s–1) and increased CO2 concentration (1100 µmol mol–1) were found to be necessary for the development of plantlets from cotyledonary stage embryos.
Key words: CO2 enrichment, chlorophyll florescence, stomata, cotyledonary embryos.
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