A Detailed Study of Adventive Embryogenesis in the Rutaceae
A Detailed Study of Adventive Embryogenesis in the Rutaceae
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Date
1973-06
Authors
Esan, Edward Babatunde
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Abstract
A Detailed Study of Adventive Embryogenesis in the Rutaceae
by
Edward Babatunde Esan
Doctor of Philosophy Graduate Program in Botany
University of California, Riverside, June, 1973
Professor Toshio Murashige, Chairman
This research explored the mechanism underlying the regulation of
adventive embryogenesis in plants, using members of the Rutaceae in
tests.
A histological comparison of Ethrog citron, a monoembryonic cultivar,
and Ponkan mandarin, a polyembryonic cultivar, disclosed no
information relevant to the research objective. Embryogenesis in vivo
in the monoembryonic cultivar followed the pattern typical of most dicot
plants. No nucellar embryogenesis occurred in the citron. The zygote
of the polyembryonic mandarin was not seen to divide. Meristematic
activity began in the nucellus prior to zygote division and resulted in
adventive embryogenesis all round the embryo sac. No embryos formed
from the nucellus epidermis. The multiplication of embryos in the
mandarin occurred largely by budding of existing embryos, rather than
continued differentiation among nucellus cells.
The histogenic pattern of polyembryogeny in Ponkan mandarin
nucellus culture was the same as that in vivo. Nucellar embryogenesis
in vitro in the monoembryonic citron cultivar was confined to the micropylar
region. Callus formation was not a prerequisite for adventive
embryogenesis in either cultivar. Occasionally, a suspensor was
observed in nucellar embryos.
Fruits obtained during the fall and winter months provided best
nucellus explants and those of spring months poorest. Best explants
were obtained when a transverse incision was made in the nucellus at
some distance from the micropylar region for the purpose of removing
embryos. Maximum embryogenesis occurred when the nucellus explant was
placed in culture with its chalazal end embedded in agar. Light was not
necessary for embryogenesis in vitro.
Nucellar embryos were obtained in ovules excised from flower buds
of several members of the Rutaceae, without prior pollination.
Test of effects of exogenous substances on nucellus cultures was
conducted with the monoembryonic cultivars, Ethrog citron and Ponderosa
lemon, and the moderately polyembryonic cultivar Eureka lemon. Embryos
were obtained in an agar medium containing only Murashige-Skoog salts
and sucrose. No addition of hormonal substances or extracts of natural
complexes showed significant benefit.
Of 31 members of the Rutaceae examined, all except one produced
adventive embryos in their nucellus cultures. The members differed only
in degree of expression of polyembryogeny in vitro.
The micropylar half of a nucellus was clearly more prone to
undergo nucellar embryogenesis than the chalazal half. Reciprocal
grafts of micropylar halves of polyembryonic and monoembryonic cultivars
resulted in no influence on embryogenesis by the one type on the other.
In grafts made between the micropylar half of the nucellus of polyembryonic
cultivars and the chalazal half of a monoembryonic cultivar,
embryogenesis in the normally polyembryonic cultivar was markedly
suppressed. This suggested that an embryogenic suppressant was involved
in the difference observed in degree of polyembryony among the Rutaceae
and between the micropylar and chalazal regions of a nucellus.
The embryogenic suppressant was graft transmissible and diffusable
through agar. Its effect was irreversible. This substance(s) also
suppressed embryogenesis in callus cultures of the wild carrot.
Description
A Dissertation submitted in partial satisfaction
of the requirements for the degree of
Doctor of Philosophy
in
Botany
by
Edward Babatunde Esan
June, 1973
Keywords
Detailed Study,, Adventive,, Adventive,, Embryogenesis,, Rutaceae