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
Apm. Rodriguez et Hy. Wetzstein, 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, Protoplasma, 204(1-2), 1998, pp. 71-83
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 develop
ment, a morphological and histological comparison was made of pecan (C
arya illinoinensis) somatic embryogenic cultures induced on media with
naphthaleneacetic acid or 2,4-dichrorophenoxyacetic acid (2,4-D), usi
ng light and scanning electron microscopy. Both auxins promoted enhanc
ed cell division, particularly in subepidermal cell layers. However, n
otable differences were observed in mitotic activity, location of embr
yogenic cell proliferation, epidermal continuity, callus growth, and e
mbryo morphology. Cultures induced on naphthaleneacetic acid had embry
ogenic regions composed of homogeneous, isodiametric, meristematic cel
ls. Embryos derived from these cultures generally had a normal morphol
ogy, were single, and had a discrete apical meristem. In contrast, tis
sues induced on media with 2,4-D had more intense and heterogeneous re
gions of cell division. Proliferating cell regions were composed of me
ristematic 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 hig
her incidence of abnormalities that included fasciated, fan-shaped, an
d tubular embryos. Defined apical meristems were often lacking or part
ially obliterated due to callus proliferation. The heterogeneous, ofte
n intensive proliferation of cells in cultures induced with 2,4-D may
interfere with normal patterns of embryo development.