The development of techniques for somatic embryogenesis in conifers has led to rapid advances in the ability to culture conifer tissue in vitro. Somatic embryogenesis now provides a means to clonally propagate commercially valuable conifers of several species and offers an in vitro experimental system for studying embryogenesis. As a result of these developments, the conifer zygotic and somatic embryo system has recently attracted the attention not only of the cell biologist but also of biochemists and molecular biologists. In this review I have attempted to consolidate the recent information on ultrastructure, biochemical and molecular aspects of conifer zygotic and somatic embryogenesis. In the first section, salient features of zygotic embryogenesis are highlighted followed by biochemical and ultrastructural characterization of development with reference to storage reserve deposition. In the second section, detailed characterization of seed storage proteins, changes in gene expression with emphasis on storage protein genes and Lea genes during zygotic and somatic embryogenesis are described. Effect of culture treatments such as abscisic acid, osmoticum and desiccation on storage protein gene expression in somatic embryos is discussed. Based on these studies, comparisons are presented between angiosperm and gymnosperm embryogeny regarding the unique morphological and developmental patterns of conifer embryogenesis. Finally, a brief discussion of recent progress in biochemical and molecular characterization of conifer seed germination is presented.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0960258500002439

Conifer zygotic embryogenesis, somatic embryogenesis, and seed germination: Biochemical and molecular advances

Comparative biochemistry of the glyoxylate cycle

Peanut (Arachis hypogaea L.) is an important nutrient-rich food legume and valued for its good quality cooking oil. The fatty acid content is the major determinant of the quality of the edible oil. The oils containing higher monounsaturated fatty acid are preferred for improved shelf life and potential health benefits. Therefore, a high oleic/linoleic fatty acid ratio is the target trait in an advanced breeding program. The two mutant alleles, ahFAD2A (on linkage group a09) and ahFAD2B (on linkage group b09) control fatty acid composition for higher oleic/linoleic ratio in peanut. In the present study, marker-assisted backcrossing was employed for the introgression of two FAD2 mutant alleles from SunOleic95R into the chromosome of ICGV06100, a high oil content peanut breeding line. In the marker-assisted backcrossing-introgression lines, a 97% increase in oleic acid, and a 92% reduction in linoleic acid content was observed in comparison to the recurrent parent. Besides, the oleic/linoleic ratio was increased to 25 with respect to the recurrent parent, which was only 1.2. The most significant outcome was the stable expression of oil-content, oleic acid, linoleic acid, and palmitic acid in the marker-assisted backcrossing-introgression lines over the locations. No significant difference was observed between high oleic and normal oleic in peanuts for seedling traits except germination percentage. In addition, marker-assisted backcrossing-introgression lines exhibited higher yield and resistance to foliar fungal diseases, i.e., late leaf spot and rust.

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Steady expression of high oleic acid in peanut bred by marker-assisted backcrossing for fatty acid desaturase mutant alleles and its effect on seed germination along with other seedling traits.

Increasing atmospheric carbon dioxide concentration, [CO2], has profound effects on growth and development of trees. Adoubling of [C02] generally stimulates photosynthesis (Murray 1995; Saxe, Ellsworth & Heath 1998) and can lead to a substantial increase in tree growth (Poorter 1993). For example, doubling [C02] increased the rate of photosynthesis per unit leaf area (A) of Pinus taeda by 14-146% (Ellsworth 1999; Liu & Teskey 1995; Thomas, Lewis & Strain 1994; Tissue et al. 1996; Tissue et al. 1997), and increased relative growth by 40-233% (DeLucia et al. 1999; Sionit et al. 1985; Thomas et al. 1994), we suggest that in very young seedlings, elevated [C02] effects may interact with internal factors such as seed N or C reserves. Thus internal and external factors that regulate growth atthe seedling stage may act acooectively to regulate subsequent seedling growth (Corbineau & Come 1995).

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Germination of CO2-enriched Pinus taeda L. seeds and subsequent seedling growth responses to CO2 enrichment

Isocitrate lyase from higher plants

The changes of isocitrate lyase levels with respect to the catabolism of triglycerides have been studied during the germination of Pinus pinea seeds. We studied the effects of octanoate, oleate, and inhibitors of protein synthesis on isocitrate lyase during germination. Pyruvate kinase, glucose-6-P-dehydrogenase, malate dehydrogenase, and isocitrate dehydrogenase were also assayed. Octanoate and oleate inhibited the isocitrate lyase activity, similarly to cycloheximide, chloramphenicol, and actinomycin, inhibitors of protein biosynthesis. This inhibitory effect is not specific but is strikingly evident with isocitrate lyase. This inhibition was not proportional to the concentration but was proportional to the chain length of oleate and octanoate.

The Effects of Octanoate and Oleate on Isocitrate Lyase Activity during the Germination of Pinus pinea Seeds.

The levels of total lipids and triglycerides were determined during germination ofLupinus seeds. The presence and operativity of the two key enzymes of the glyoxylate cycle, isocitrate lyase and malate synthase, were made clearly evident and correlated to lipid metabolism. An oil, relatively free of erucic acid, was obtained from the seeds at 0 germination time.

The composition and utilization of lipids and the operativity of the glyoxylate cycle during the germination ofLupinus seeds

During our investigation on the effect of some fatty acids on the germination of Pinus pinea seeds (Vincenzini et al., 1973), we noted a marked decrease of G6PDH activity when octanoate or oleate were added to the culture medium. In an attempt to provide biochemical information on the effect of free fatty acids on G6PDH activity, in vivo, during Pinus pinea seeds germination, we tested different concentrations of octanoate and oleate added to the culture medium. Moreover other enzymes of fundamental metabolic pathways were also considered, particularly 6PGDH, the second enzyme of HMS.

M. T. Vincenzini

Papers

The Effects of Octanoate and Oleate on Isocitrate Lyase Activity during the Germination of Pinus pinea Seeds.

The composition and utilization of lipids and the operativity of the glyoxylate cycle during the germination ofLupinus seeds

In vivo effects of octanoate and oleate on glucose-6-phosphate dehydrogenase during germination of Pinus pinea seeds.