Somatic embryogenesis of Pinus patula Scheide et Deppe.
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Date
1994
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Abstract
Immature, green female cones of Pinus patula Scheide et Deppe. were collected on a weekly
basis during the South African summer months from December 1991 to February 1992 and
from December 1992 to March 1993. Embryogenic tissue was initiated from excised
megagametophyte explants containing immature zygotic embryos. Embryogenic induction
was achieved using both MSG (BECWAR, NAGMANI & WANN 1990) and DCR (GUPTA
& DURZAN 1985) media. The highest induction frequency was obtained on DCR1
(Douglas-fir Cotyledon Revised) medium supplemented with 0.5 mg 1 ¯¹ BA and 3.0 mg 1 ¯¹
2,4-D, using L-glutamine as the major nitrogen source. Embryogenic tissue was translucent-to-
white and mucilaginous in nature, composed of elongated, suspensor-like cells. The tissue
was extruded from the micropylar end of the female gametophyte. In comparison, nonembryogenic
tissue was produced from the gametophytic tissue itself and consisted of small,
compact, spherical cells, crystalline in nature. Anatomical studies of developing patula seed
demonstrated that the production of embryogenic tissue from the immature explants co-incided
with the period, approximately two weeks after fertilization and with the occurrence of
cleavage polyembryony in the developing zygotic embryos. Embryogenic tissue was
maintained in culture by a recapitulation of the cleavage process.
Transfer of the embryogenic tissue to DCR2 medium containing 1.3 mg 1 ¯¹ ABA resulted in
tissue maturation and in the subsequent development of somatic embryos. Presence of ABA
in the culture medium stimulated the development of cotyledonary initials in the apical region
of the embryos. Elongated embryos, possessing small cotyledons, were rooted (50 to 60 %)
on MSG6 medium containing no plant growth regulators. Somatic plantlets were successfully
hardened-off under greenhouse conditions.
Liquid culture methods were found to be a useful means of rapidly increasing the volume of
embryogenic suspensor masses. Maturation , in terms of somatic embryo development and
the production of cotyledonary initials, though , was not obtained in suspension. Reestablishment
onto agar-solidified medium (DCR2) was required before maturation could occur. ABA is also responsible for stimulating reserve deposition and mobilization. In this
regard, lipid accumulation in the developing somatic embryos was quantified and found to be
significantly lower than in developing zygotic embryos. Similarly, non-matured embryogenic
tissue contained less lipid deposits than matured (ABA-treated) tissue, indicating the
requirement for ABA during maturation. Quantification of the lipids deposits is useful in
determining the potential for somatic embryos to acclimatize to ex vitro conditions since their
further growth and development is based on their ability to accumulate storage reserves.
Somatic embryogenesis was found to be a useful method of propagation, producing plantlets
with seedling-like qualities. This development has important consequences for the production
of clonal plantlets in the Forestry Industry.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.
Keywords
Pinus patula--Propagation., Theses--Botany.