A morphological and histological comparison of the initiation and development of pecan (Carya illinoinensis) somatic embryogenic cultures induced with naphthaleneacetic acid or 2,4-dichlorophenoxyacetic acid

Abstract

Summary. Somatic embryos produced in vitro may exhibit structural abnormalities that affect their subsequent germination and conversion into plants. To assess the influence of auxin type on embryo initiation and development, a morphological and histological comparison was made of pecan (Carya illinoinensis) somatic embryogenic cultures induced on media with naphthaleneacetic acid or 2,4-dichlorophenoxyacetic acid (2,4-D), using light and scanning electron microscopy. Both auxins promoted enhanced cell division, particularly in subepidermal cell layers. However, notable differences were observed in mitotic activity, location of embryogenic cell proliferation, epidermal continuity, callus growth, and embryo morphology. Cultures induced on naphthaleneacetic acid had embryogenic regions composed of homogeneous, isodiametric, meristematic cells. Embryos derived from these cultures generally had a normal morphology, were single, and had a discrete apical meristem. In contrast, tissues induced on media with 2,4-D had more intense and heterogeneous regions of cell division. Proliferating cell regions were composed of meristematic cells interspersed with callus and involved more extensive regions of the mesophyll. Marked callus proliferation caused epidermal rupture in some areas. Embryos induced on medium with 2,4-D had a higher incidence of abnormalities that included fasciated, fan-shaped, and tubular embryos. Defined apical meristems were often lacking or partially obliterated due to callus proliferation. The heterogeneous, often intensive proliferation of cells in cultures induced with 2,4-D may interfere with normal patterns of embryo development.

In vitro organogenesis in watermelon cotyledons

“…Explants cultivated in organogenesis induction medium, containing BAP (1.0 mg L -1 ) and coconut water (10%), were sampled for histological study after 21 days in culture, according to Rodriguez & Wetzstein (1998). Samples were fixed in paraformaldehyde (3%) and glutaraldehyde (2%), in cacodylate buffer (0.2 M, pH 7.2) under refrigeration, for five days.…”

Histological changes in banana explants, cv. Nanicão (Musa spp., Group AAA), submitted to different auxins for induction of somatic embryogenesis

“…Somatic embryos formed in the embryogenic regions were also sampled for histological comparison. All samples were fixed according to Rodriguez & Wetzstein (1998), in paraformaldehyde (3%, w/v) and glutaraldehyde (2% v/v) in cacodylate buffer (0.2 M, pH 7.2) under refrigeration, with the first hour under low vacuum. Fixed tissues were slowly dehydrated at room temperature in a series of ethanol (35-100%), followed by infiltration at 4 °C overnight, in etanol:infiltration medium (Historesin, Leica) (1:1).…”

“…maturation and conversion into plants. The choice of auxin is very important in the induction process and can affect the frequency and morphology of somatic embryos (Lazzeri et al 1987, Levi & Sink 1991, Rodriguez & Wetzstein 1994, 1998. Somatic embryogenesis of banana cultivars of different groups has been successfully achieved (Novak et al 1989, Dedh'a et al 1991, Côte et al 1996, Escalant et al 1994, Grapin et al 1996, however, the conversion into plants is frequently low, thus limiting its association with genetic transformation techniques.…”

Anomalous somatic embryos in Acca sellowiana (O. Berg) Burret (Myrtaceae)

“…It is also used as a technique to propagate plants in large scale (Gray & Purohit 1991) but at the same time it is a prominent source of somaclonal variation (Larkin & Scowcroft 1981) in a representative number of plants (Lazzeri et al 1987, Fourré et al 1997, Rodriguez & Wetzstein 1998, Dedicová et al 2000, Wilhelm et al 2005. This certainly reduces the potential of somatic embryogenesis for phytotechnical purposes.…”