hmeekes at BIOSCI.MBP.MISSOURI.EDU
Mon Jun 19 08:38:39 EST 1995
On June 16 1995 markradon at etoncomp.demon.co.uk wrote:
>>Where does this plant get its mitochondria from?
>>Do pollen grains have mitochondria? If so, how come mitochondrial DNA is
>>always inherited down the maternal line?
Then LEWINSON at WSUVM1.CSC.WSU.EDU wrote on June 17 1995
>Your question about mitochondria in anther culture is a very interesting one.
>By the way, unlike most angiosperm pollen, the pollen from conifers does
>contain mitochondria. My guess is that angiosperm pollen must contain some
>mitochondria too, but is probably non-functional during normal fertilization.
People at the Department of Experimental Botany in Nijmegen, The
Netherlands have exetnsively studied pollen from Lilium and Tobacco
(Nicotiana) using light and electron microscopical techniques. Their
results show that mitochondria are plentyful in these pollen. These
mitochondria obviously are active during the growth of the pollen tube,
which starts after the arrival of the pollen grain on the stigma (or in the
in vitro culture medium). Considering that the pollen grain will grow a
tube that is hugely long compared to the size of the grain, nutrient sugars
must be taken up from the surrounding tissue and converted into energy in
the pollen tube's own organelles.
To understand the maternal lineage of mitochondria it is important to note
that pollen usually consists of a generative cell (nucleus) which serves
for ferilization only and which more or less behaves like an organelle in
the cell, as it moves (freely) in the pollen tube, and does not need
mitochondria. The actual pollen tube growth, as well as the movement of the
generative cell is regulated by the vegetative cell/nucleus that also
supplies the energy for this process. As Marco Bleeker pointed out well,
the vegetative cell forms a small gametophyte, with the generative nucleus
as the actual, fertilizing nucleus.
For references and more information check out papers by Kroh, Knuiman
and/or Rutten in e.g. Planta, Protoplasma and Acta Botanica Neerlandica.
Hope this helps carify your question.
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