We describe the construction of new helper Ti plasmids forAgrobacterium-mediated plant transformation. These plasmids are derived from three differentAgrobacterium tumefaciens Ti plasmids, the octopine plasmid pTiB6, the nopaline plasmid pTiC58, and the L,L-succinamopine plasmid pTiBo542. The T-DNA regions of these plasmids were deleted using site-directed mutagenesis to yield replicons carrying thevir genes that will complement binary vectorsin trans. Data are included that demonstrate strain utility. The advantages ofAgrobacterium strains harbouring these ‘disamed’ Ti plasmids for plant transformation viaAgrobacterium are discussed.

New Agrobacterium helper plasmids for gene transfer to plants

Somatic embryogenesis is defined as a process in which a bipolar structure, resembling a zygotic embryo, develops from a non-zygotic cell without vascular connection with the original tissue. Somatic embryos are used for studying regulation of embryo development, but also as a tool for large scale vegetative propagation. Somatic embryogenesis is a multi-step regeneration process starting with formation of proembryogenic masses, followed by somatic embryo formation, maturation, desiccation and plant regeneration. Although great progress has been made in improving the protocols used, it has been revealed that some treatments, coinciding with increased yield of somatic embryos, can cause adverse effects on the embryo quality, thereby impairing germination and ex vitro growth of somatic embryo plants. Accordingly, ex vitro growth of somatic embryo plants is under a cumulative influence of the treatments provided during the in vitro phase. In order to efficiently regulate the formation of plants via somatic embryogenesis it is important to understand how somatic embryos develop and how the development is influenced by different physical and chemical treatments. Such knowledge can be gained through the construction of fate maps representing an adequate number of morphological and molecular markers, specifying critical developmental stages. Based on this fate map, it is possible to make a model of the process. The mechanisms that control cell differentiation during somatic embryogenesis are far from clear. However, secreted, soluble signal molecules play an important role. It has long been observed that conditioned medium from embryogenic cultures can promote embryogenesis. Active components in the conditioned medium include endochitinases, arabinogalactan proteins and lipochitooligosaccharides.

https://link.springer.com/content/pdf/10.1023/A:1015673200621.pdf

Developmental pathways of somatic embryogenesis

Section A 1 Somatic Embryogenesis in White Spruce: Studies of Embryo Development and Cell Biology L Kong, et al 2 Proliferative Somatic Embryogenesis in Woody Species K Raemakers, et al 3 Somatic Embryo Germination and Desiccation Tolerance in Conifers EI Hay, PJ Charest 4 Performance of Conifer Stock Produced Through Somatic Embryogenesis SC Grossnickle 5 Apoptosis During Early Somatic Embryogenesis in Picea spp L Havel, DJ Durzan 6 Water Relation Parameters in Conifer Embryos: Methods and Results N Dumont-Beboux, et al 7 Image Analysis for Sorting Somatic Embryos Y Ibaraki 8 Somatic Embryogenesis in Woody Legumes RN Trigiano, et al 9 Cold Storage and Cryopreservation of Camellia Embryogenic Cultures AM Vieitez, A Ballester 10 Cryopreservation of Embryogenic Cultures of Conifers and Its Application to Clonal Forestry DR Cyr 11 Commercialization of Plant Somatic Embryogenesis BCS Sutton, DR Polonenko Section B 12 Somatic Embryogenesis in Myrtaceous Plants JM Canhoto, et al 13 Somatic Embryogenesis Induction in Bay Laurel (Laurus nobilis L) JM Canhoto, et al 14 Somatic Embryogenesis in Simarouba glauca Linn GR Rout, P Das 15 Somatic Embryogenesis in Magnolia spp SA Merkle 16 Somatic Embryogenesis and Evaluation of Variability in Somatic Seedlings of Quercus serata by RAPD Markers K Ishii, et al 17 Somatic Embryogenesis from Immature Fruit of Juglans cinerea PM Pijut Section C 18 Somatic Embrygonesis in Pinus patula Scheide et Deppe NB Jones, J van Staden 19 Somatic Embryogenesis in African Cycads (Encephalartos) AK Jager, J van Staden 20 Somatic Embryogenesis in Picea wilsonii Y Yang, Z Guo 21 Somatic Embryogenesis in Jack Pine (Pinus banksiana Lamb) YS Park, et al 22 Somatic Embryogenesis in Hybrid Firs J Jasik, et al 23 Somatic Embryogenesis in Taxus SR Wann, et al

Somatic embryogenesis in woody plants

This is a short review of the classical and new, natural and synthetic plant hormones and growth regulators (phytohormones) and highlights some of their uses in plant tissue culture. Plant hormones rarely act alone, and for most processes— at least those that are observed at the organ level—many of these regulators have interacted in order to produce the final effect. The following substances are discussed: (a) Classical plant hormones (auxins, cytokinins, gibberellins, abscisic acid, ethylene and growth regulatory substances with similar biological effects. New, naturally occurring substances in these categories are still being discovered. At the same time, novel structurally related compounds are constantly being synthesized. There are also many new but chemically unrelated compounds with similar hormone-like activity being produced. A better knowledge of the uptake, transport, metabolism, and mode of action of phytohormones and the appearance of chemicals that inhibit synthesis, transport, and action of the native plant hormones has increased our knowledge of the role of these hormones in growth and development. (b) More recently discovered natural growth substances that have phytohormonal-like regulatory roles (polyamines, oligosaccharins, salicylates, jasmonates, sterols, brassinosteroids, dehydrodiconiferyl alcohol glucosides, turgorins, systemin, unrelated natural stimulators and inhibitors), as well as myoinositol. Many of these growth active substances have not yet been examined in relation to growth and organized developmentin vitro.

Plant hormones and plant growth regulators in plant tissue culture

Synthetic seed technology requires the inexpensive production of large numbers of high-quality somatic embryos. Proliferating embryogenic cultures from conifers consist of immature embryos, which undergo synchronous maturation in the presence of abscisic acid and elevated osmoticum. Improvements in conifer somatic embryo quality have been achieved by identifying the conditions in vitro that resemble the conditions during in ovulo development of zygotic embryos. One normal aspect of zygotic embryo development for conifers is maturation drying, which allows seeds to be stored and promotes normal germination. Conditions of culture are described that yield mature conifer somatic embryos that possess normal storage proteins and fatty acids and which survive either partial drying, or full drying to moisture contents similar to those achieved by mature dehydrated zygotic embryos. Large numbers of quiescent somatic embryos can be produced throughout the year and stored for germination in the spring, which simplifies production and provides plants of uniform size. This review focuses on recent advances in conifer somatic embryogenesis and synthetic seed technology, particularly in areas of embryo development, maturation drying, encapsulation and germination. Comparisons of conifer embryogeny are made with other gymnosperms and angiosperms.

Embryogeny of gymnosperms: advances in synthetic seed technology of conifers

The germination of mature somatic embryos of interior spruce was limited by the low frequency of root emergence. In addition, development was abnormal, since elongation and greening of the hypocotyl and cotyledons preceded root emergence by 1–2 weeks. Pretreatment of the embryos on water-saturated Kim-paks increased the frequency of root emergence but did not alter the abnormal pattern of germination. Somatic embryos do not survive desiccation at room humidity, but partial drying at high humidity promoted germination up to 90%. Furthermore, this treatment decreased the time required for root emergence such that elongation of the root and hypocotyl–cotyledon was synchronized over a period of 5–6 days. This germination closely resembled that of excised zygotic embryos. Drying over a range of humidities indicated that humidities of 81% and lower were lethal to the embryos, whereas germination was enhanced following treatment at humidities greater than 95% relative to untreated controls. The best germination ...

Synchronous and high frequency germination of interior spruce somatic embryos following partial drying at high relative humidity

The ontogenetic course followed by somatic embryos of interior spruce is highly dependent on the media concentration of abscisic acid (ABA). Little or no organized development occurs in the absence of ABA and as the level of ABA is increased, a range of embryo types is produced. “Shooty embryo” structures predominate in many callus lines at low levels of ABA (1-10 μM), while 10-20 μM ABA promotes the formation of bipolar embryos that germinate precociously. When ABA is increased to 30-40 μM, precocious germination is inhibited and opaque cotyledonary embryos characteristic of their zygotic counterparts are formed which enter a period of quiescence. Only “mature” somatic embryos contain significant amounts of storage proteins and the level to which these proteins accumulate is dependent on the concentration of ABA. Indole-butyric acid (IBA) included with ABA increases the number of mature embryos. Root elongation, which was used as a measure of embryo quality, was never observed from shooty embryo Structures and was 2-3 fold higher in mature embryos compared to those that germinated precociously.

Abscisic acid and indole‐3‐butyric acid regulation of maturation and accumulation of storage proteins in somatic embryos of interior spruce

To apply somatic embryogenesis to clonal propagation of forest species, the technique must be applicable to a broad range of genotypes and allow efficient regeneration of phenotypically normal plants. Seventy-one lines (genotypes) of embryogenic cultures from six open-pollinated families were obtained by culturing immature embryos of interior spruce. Interior spruce represents a mixture of two closely related species, Piceaglauca (Moench) Voss and Piceaengelmannii Parry, from the interior of British Columbia where they hydridize with one another. The abscisic acid dependent developmental profile (the proportion of rooty embryos, shooty embryos, precociously germinating embryos, and mature embryos over a range of abscisic acid concentrations) differed among genotypes, but in general, production of mature somatic embryos was highest at 40 and 60 μM abscisic acid. Treatment of mature embryos with a high relative humidity treatment resulted in partial drying of the embryos and upon rehydration, markedly enhan...

Propagation of interior spruce by somatic embryogenesis.

Low levels of mannitol (2–6%) promoted the formation of globular embryos in embryogenic cultures of interior spruce (Picea glauca engelmanni complex). However, these concentrations of mannitol were inhibitory to the formation of cotyledonary embryos. A short (1 week) pulse of mannitol in combination with abscisic acid doubled the production of late cotyledonary somatic embryos compared with the standard abscisic acid treatment. Higher levels of mannitol (13 and 20%) were required to inhibit precocious germination of spruce somatic embryos. These concentrations of mannitol promoted the accumulation of storage proteins during cotyledon maturation, but were not as effective as abscisic acid. Furthermore, 13 and 20% mannitol treatments did not substitute for abscisic acid in promoting the formation of cotyledonary embryos. Pre-treatment of late cotyledonary embryos with mannitol (13–25%) did not increase the frequency of germination compared with germination in non-treated embryos (approximately 10% germinated) although dehydration with high relative humidity treatment increased germination to 83%.

Abscisic acid and mannitol promote early development, maturation and storage protein accumulation in somatic embryos of interior spruce

Embryogenic cultures of interior spruce derived from 12 full-sib families were subjected to cryopreservation, with a 97 % success rate for 357 genotypes. Analyses suggested that cryotolerance was not related to family ranking (height increment), embryogenic potential or culture dispersability in suspension, and long-term storage in or above liquid nitrogen did not affect regenerative potential. By contrast, differences in cryotolerance among cell lines appeared to be prevalent in certain families. Analysis with a DNA fingerprinting probe used for clonal identification demonstrated no evidence of somaclonal variation as a result of cryopreservation. The results of this work indicate the applicability of cryopreservation as a long-term storage strategy for spruce embryogenic cultures from a wide genetic background.

Dane R. Roberts

Papers

Synchronous and high frequency germination of interior spruce somatic embryos following partial drying at high relative humidity

Abscisic acid and indole‐3‐butyric acid regulation of maturation and accumulation of storage proteins in somatic embryos of interior spruce

Propagation of interior spruce by somatic embryogenesis.

Abscisic acid and mannitol promote early development, maturation and storage protein accumulation in somatic embryos of interior spruce

Cryopreservation of interior spruce (Picea glauca engelmanni complex) embryogenic cultures.