Maturation of Soybean Somatic Embryos and the Transition to Plantlet Growth

Abstract

MATERIALS AND METHODS The maturation of soybean (Glycine max L. Merr.) somatic embryos was characterized. Maturation was assayed by evaluating the ability of somatic embryos to make the transition to a plantlet through a germination-like process. Somatic embryos were organized from cotyledons of immature soybean embryos. Maturation of somatic embryos occurred on a Murashige-Skoog basal medium supplemented with activated charcoal and 0.28 molar sucrose. After 8 weeks on this medium, somatfc embryos exhibited vigorous, high frequency development to plantdets. The "germination" frequency (conversion) of somatic embryos, and plantlet recovery frequency varied concurrently with maturation period. Conversion and plant recovery required no exogenous growth regulators. Desiccation of immature somatic embryos under controlled humidity regimes resulted in increased frequency of conversion of immature somatic embryos. Morphological abnormalities appeared in the somatic embryos, but few were detrimental to conversion velocity. There was little effect of genotype on conversion velocity or frequency.There have been several contemporary reports concerning the production of somatic embryos from cotyledons of immature soybean embryos (5,6,15,23,24). Although considerable effort has been expended in the characterization of somatic embryo induction, there is sparse quantitative information on the subsequent performance of the somatic embryos, especially with regard to their morphology, anatomy, development, physiology, and biochemistry. Although somatic embryogeny recapitulates zygotic embryology in many ways (7,22,28), this correlation has yet to be developed in soybean. Plant cell and tissue culture provides an excellent opportunity to study developmental processes in a controlled environment. However, cell and tissue cultures typically are not well-synchronized in development or differentiation. Therefore, the goals of this study are to understand the processes of soybean somatic embryo development, and to control expression of this process in a reproducible and controlled fashion. Our long-term goal is to determine if the requirements for somatic embryo maturation and development are comparable to that demanded by zygotic embryos. In this way, somatic embryos may function as a model for zygotic embryogenesis. ' Induction and Maturation of Somatic EmbryosSomatic embryos were generated on cotyledons of immature soybean (Glycine max L. Merr.) embryos as described by Ranch et al. (23,24). The genotypes used in these studies were cv 'Gem,' 'Star,' 'Shawnee,' 'A3127,' 'Williams 82,' and 'Union.' Immature seed were harvested from greenhouse or field-grown plants. At the appropriate stage for explant, the immature embryo possessed cotyledons 3 to 5 mm long and were 15 to 21 DAF in field-grown plants. Cotyledons were cultured abaxial surface down on solidified induction medium composed of Murashige and Skoog (17) Growth and Different during the Maturation RegimeAt the time of initial transfer to MM, and at intervals for 70 ...

Improvement of soybean somatic embryo development and maturation by abscisic acid treatment

“…Increased viability and germination frequency suggested that embryos treated with ABA are physiologically more mature. Maturation of somatic embryos is a process during which a large amount of nutrients accumulate (Buchheim et al 1989). ABA has been reported to stimulate protein accumulation of soybean zygotic embryos cultured in vitro during the early phase of embryogenesis (Ackerson 1984).…”

“…After formation, somatic embryos require a long time (ca. 60 d) for growth, development and maturation (Buchheim et al 1989;Baily et al 1993a). The embryo germination frequency is also low (0-5%, Parrott et al 1988) and requires complex manipulations (Buchheim et al 1989;Baily et al 1993b).…”

“…60 d) for growth, development and maturation (Buchheim et al 1989;Baily et al 1993a). The embryo germination frequency is also low (0-5%, Parrott et al 1988) and requires complex manipulations (Buchheim et al 1989;Baily et al 1993b). To date, soybean still remains conspicuous among major crops with respect to practical use of somatic embryogenesis and genetic engineering.…”

“…Since the initial reports of plant regeneration from somatic embryos in soybean, various culture conditions and growth regulators have been investigated (Lazzeri et al 1987;Hartweck et al 1988;Parrott et al 1988;Buchheim et al 1989;Bailey et al 1993a;Santarem et al 1997;Samoylov et al 1998). However, soybean somatic embryogenesis is still less developed and less efficient in comparison to many major crop species.…”

Effect of air desiccation and salt stress factors on in vitro regeneration of rice (Oryza sativaL.)

“…35 Three and 4 hours desiccated calli reduced fresh weight due to reduction of water content and stimulated callus growth, globularization and embryo formation in 2 date palm cultivars. 31 Desiccation also has been reported to promote somatic embryo differentiation and development to other crops like as soybean, 36,37 wheat, 38 spruce 39 and cassava. 40 In recent years tissue culture techniques are being used as a useful tool to elucidate the mechanism involved in salt tolerance.…”