Somaclonal variation during interior spruce (Picea glauca engelmannii complex) somatic embryogenesis was evaluated using culture morphology and isozyme analysis. Genotype-specific abscisic acid-dependent developmental profiles and isozyme patterns were similar for subclone and parent line embryogenic cultures and cotyledonary somatic embryos. Extensive analysis of fifteen hundred subclone embryos of one genotype revealed no isozyme pattern variation. Initiation of embryogenic cultures was dependent on the developmental stage of the explant although cultures derived from different stages were morphologically similar. The embryogenic cultures initiated from interior spruce embryos show a high degree of genetic stability in that the morphological behavior and isozyme phenotype were always consistent with that of the explant genotype. These results support the conclusion that this culture system is appropriate for clonal propagation of interior spruce.

Photosynthetic response to water stress was analyzed in 1-year-old interior spruce (Picea glauca (Moench) Voss x P. engelmanni Parry hybrid complex) seedlings and emblings produced from somatic embryogenesis. Carbon dioxide uptake, oxygen evolution and chlorophyll fluorescence at 20 degrees C were monitored as predawn shoot water potential (Psi) decreased. Concurrently with stomatal closure, carbon assimilation declined rapidly as Psi decreased to -1.0 MPa. Oxygen evolution at 10,000 micro l CO(2) l(-1) declined continuously as Psi decreased to -1.6 MPa. At photon flux densities (PFD) above 50 micro mol m(-2) s(-1), photochemical efficiency of photosystem (PS) II observed during actinic light exposure (Phi(II), calculated as DeltaF/F(m)') decreased as Psi decreased. At the same PFDs, photochemical quenching (q(P)) declined with decreasing Psi and nonphotochemical quenching (q(N)) increased steadily. At PFDs below 50 micro mol m(-2) s(-1), major decreases in q(N) were not observed until Psi decreased below -1.6 MPa. We identified three phases of photosynthetic response to progressive water stress in interior spruce: a pronounced decline in gas exchange, subsequent photoprotective changes in chlorophyll fluorescence as primary photochemistry was down-regulated, and a decline in photochemical efficiency of dark-adapted needles.

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