This review describes sources of structures of non-microspore origin observed in anther and microspore cultures. Various characteristics of these structures may cause a wrong diagnosis of these structures as embryos or cell/tissue clusters of microspore origin. Here we suggest such structures to be named as pseudoembryogenic structures. The introduction of pseudo-embryogenic structures and their origins could be helpful to distinguish them from true microspore-derived structures. Prompted by certain environmental cues, somatic cells existing as a contamination in immature pollen (microspores) cultures can lead to the formation of 'pseudo-embryos' commonly known as embryoids. The pseudo-embryogenic structures may be classified in the following groups: (i) pseudo-star-like structures; pseudo-multicellular structures; (ii) pseudo-embryos with pseudo-suspensors; (iii) contaminating bacteria appearing as callus colonies; (iv) calli and embryos of somatic origin; (v) giant tetrad-like structures; (vi) anther wall cells. The exact origin of these structures is discussed in this paper, and some recommendations are proposed in order to avoid misinterpretation.
Purple coneflower (Echinacea purpurea (L.) Moench) is a widely used medicinal and ornamental plant. In the present study, the callus embryogenesis was examined using benzyl adenine (BA) at three levels (3, 4, 5 mg L−1), 1-Naphthalene acetic acid (NAA) at three levels (0.1, 0.2 and 0.5 mg L−1) with or without activated charcoal (1 g L−1), coconut milk (50 ml L−1) and casein hydrolysate (50 mg L−1) in the MS (Murashige and Skoog 1962) medium. The embryogenesis indirectly occurred with the production of callus. The calli were observed in three forms: undifferentiated, embryogenic and organogenic. The embryogenic calli were dark green and coherent with a faster growth rate. The highest embryogenesis (100%) and embryonic regeneration (plantlet production) were obtained in the combined BA + NAA treatments with the activated charcoal, coconut milk and casein hydrolysate. However, the combined treatments of growth regulators failed to produce somatic embryos without the use of coconut milk and casein hydrolysate. The maximum amount of protein, peroxidase and catalase activity of embryogenic calli (2.02, 1.79 and 6.62ΔOD/Min/mg.protein, respectively), and highest percentage of acclimatization success (29.3% of plants) were obtained in the combined treatment of 5 mg L−1 BA + 0.5 mg L−1 NAA + activated charcoal + coconut milk + casein hydrolysate. The highest amount of chlorophyll content (33.3 SPAD value) and growth characteristics of acclimatized plantlets were observed in the media containing 3 mg L−1 BA + 0.1 and 0.2 mg L−1 NAA + 1 g. L−1 combined activated charcoal, coconut milk, casein hydrolysate. The histological studies confirmed the somatic embryogenesis in purple coneflower. Generally, it was found that the somatic embryogenesis of E. purpurea occurs at high levels of BA and low levels of NAA with the addition of coconut milk and casein hydrolysate.
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