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Since the first report of somatic embryogenesis in Norway spruce in 1985, the in vitro process has been initiated for a number of conifer species belonging to different genera. The process of somatic embryogenesis involves initiation, proliferation, maturation and plantlets (emblings) regeneration. The initiation of somatic embryogenesis is restricted mostly to juvenile explants, although recently explants taken from adult trees produced embryogenic tissues. The successful initiation, maturation and emblings regeneration are affected by factors as developmental stage of primary explants, genotype, plant growth regulators content in the culture medium, light conditions. Optimisation of mentioned factors resulted in regeneration of emblings capable of growing after transfer to soil.
Embryogenic cell line AN 72 derived from immature hybrid fir Abies alba x A. numidica zygotic embryos was subjected to different maturation treatments. The effect of the carbohydrates sucrose, maltose and glucose (each at 3%, 6% and 9%) or PEG-4000 (5.0%, 7.5% and 10%) combined with different carbohydrate sources was tested. PEG-4000 stimulated somatic embryo maturation of hybrid fir. This stimulatory effect was dependent on the carbohydrate source used. Culture medium with maltose as carbohydrate source combined with PEG-4000 produced the highest number of cotyledonary somatic embryos. Carbohydrates supplied alone (mainly at 6% and 9%) exerted an unfavorable effect, increasing the frequency of abnormally shaped somatic embryos without regeneration capacity. The structural organization of morphologically well-developed cotyledonary somatic embryos was similar to that of zygotic embryos. In abnormal somatic embryos the shoot apical meristem and root meristem were very damaged. Electrophoretic separation of denatured proteins using SDS-PAGE showed differences in the accumulation of low molecular weight storage proteins in somatic embryos. Storage protein accumulation was dependent on the concentration of PEG-4000 and the carbohydrate source.
The paper reports a comparative study of storage protein synthesis and enzyme activity during zygotic and somatic embryogenesis of silver fir. The SDS-PAGE profiles of storage proteins in zygotic and somatic embryos were similar but not identical. Six storage protein fractions were detected in zygotic embryos, as compared with eleven fractions in somatic embryos. The principal storage protein of zygotic embryos was represented by the 43 kDa fraction, and in somatic embryos by the 53 kDa fraction. Peroxidase activity was lower in the precotyledonary and cotyledonary stages of somatic embryos than in the corresponding developmental stages of zygotic embryos. However, following desiccation, the mature somatic embryos possessed three times higher peroxidase activity than the mature zygotic embryos. The reverse was true of the specific activity of esterase, which was higher in zygotic embryos than in somatic embryos in all stages of development.
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