SECRETION OF SPECIFIC EXTRACELLULAR PROTEINS BY SOMATIC EMBRYOS OF PICEA-ABIES IS DEPENDENT ON EMBRYO MORPHOLOGY

Embryogenic cell lines of Picea abies were categorized into two groups , A and B, based on the morphology of the, somatic embryos and the abi lity of the somatic embryos to proceed through a maturation process wh en treated with ABA. Group A embryos had a distinct, densely-packed em bryonic region whereas group B embryos had loosely packed cells in the ir embryonic region. Embryo morphology was shown to be regulated by ch anges in the plant growth regulators in the culture medium. Treatment with N-6-benzyladenine stimulated embryos to develop large embryonic r egions. The morphology of somatic embryos and especially that of the e mbryonic regions was correlated with the presence of specific extracel lular proteins. Only somatic embryos with densely packed cells in the embryonic regions secreted proteins with relative molecular weights of 28, 66 and 85 kD. The extracellular protein of 28 kD was isolated and the first 21 amino acids in the N-terminus were identified. These sho wed 52-57 % identity with the N-terminal sequence conserved among memb ers of a protein family which includes zeamatin and which have been sh own to be involved in plant anti-fungal mechanisms. Immunological stud ies of extracellular chitinases and zeamatin-like proteins, as well as of activity of extracellular peroxidase, revealed a close correlation between the presence of specific chitinases and embryo morphology. (C ) 1996 Annals of Botany Company