New Zealand Journal of Botany abstracts
Embryology of two threatened species of Pachycladon (Brassicaceae)
C. Luo
Landcare Research
P.O. Box 69
Lincoln 8125, New Zealand
R. A. Bicknell
Crop & Food Research
Private Bag 4707
Christchurch, New Zealand
P. B. Heenan*
Landcare Research
P.O. Box 69
Lincoln 8125, New Zealand
Abstract Ovule development and embryogenesis are described
for Pachycladon exilis and P. cheesemanii using thin sectioning
of resin-embedded tissue. The structures of megasporogenesis and embryogenesis
in these two species of Pachycladon were similar to those described
for Arabidopsis thaliana. There was, however, a significant difference
in the timing of events, with an extended delay apparent in Pachycladon
between anther dehiscence and the first cell divisions of the embryo and
endosperm. Initial endosperm development in the two Pachycladon species
was of the free nuclear type, followed by cellularisation in a manner similar
to that seen in Arabidopsis. Within one day of anthesis a chalazal
proliferating tissue mass developed adjacent to the chalazal pole of the
embryo sac. However, free nuclear division of endosperm nuclei was not observed
until 7 days after anther dehiscence. The stages of embryogenesis for the
two Pachycladonspecies were approximately correspondent in time, but
the final silique length and rate of silique elongation of P. cheesemaniiwas
greater than for P. exilis. The siliques of P. cheesemanii also took
at least an extra 7 days to desiccate at maturity.
Keywords Brassicaceae; Pachycladon exilis; Pachycladon
cheesemanii; embryogenesis; histology; silique length; New Zealand flora
*Author for correspondence
B02037 Received 1 May 2002; accepted 29 October 2002; published 31 March
2003
New Zealand Journal of Botany, 2003, Vol. 41: 171-178
0028-825X/03/4101-0171 $7.00 © The Royal Society of New Zealand
2003
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