W10 Prac questions Flashcards
How would you show if a newly identified plant species is self-compatible or not at
the fertility level? And if it was self-incompatible, how would you check if it is gametophytic or sporophytic self-incompatible, knowing that you can observe the germination of the pollen tubes under the microscope?
First, a few plants of this species would have to be self fertilised (pollinated with
only its own pollen) to determine if they produce any seeds (self-compatible) or not
(self incompatible). Second, if the plants are self-incompatible, they would have to
be crossed to several different other plants (of the same species). Upon crossing, the
pollen germination on the stigma would be observed with aniline blue. Let us assume, that in all viable crosses, each of the pollen grains on the stigma successfully germinated and fully elongated their pollen tubes. This would suggest a sporophytic self-incompatibility system. If in some crosses only half of the pollen grains germinated and fully elongated their pollen tube, one would assume a gametophytic self-incompatibility system.
The currently accepted model of sporophytic self-incompatibility states that this is conferred by factors (proteins etc. originated in the sporophytic tissue of the male -anthers) that coat the outer layer of the pollen grain (exin). However, in Brassica (in a sporophytic self-incompatible species) it has been shown that the expression of at
least one factor conferring self-incompatibility occurs in the pollen grain and not in the sporophytic tissue of the parental plant. Using your knowledge about sporophytic self-incompatibility model, and anther morphology, how would you explain that a gene only expressed in half the haploid pollen grains in the anther, will also confer sporophytic self-incompatibility to all the pollen grains in the anther.
According to some models, the sporophytic self-incompatibility could be either
conferred by proteins originated in the sporophytic tissue, and hence deposited on
the pollen coat of all pollen grains, or as asked in this question, the protein could be
exported from the pollen grain into the anther locus, where it would be deposited on
the pollen coats of all the pollen grains present in the anther, regardless of their haplotype.
For the pollen tube to reach its goal (fertilisation of the egg cell nucleus and central cell nucleus in the ovule) it requires signals to guide it down the stigma, style and towards the ovules. A research group in Japan, showed that the destruction of one of the synergids affected slightly the entrance of the pollen tube into the ovule while the destruction of both abolished it. What would you conclude from this experiment? Do you think, from what you have learned, if this is the only cue required for pollen tube guidance?
From this experiment I would conclude that the synergids are required to direct the
pollen tube into the ovule, and that one is sufficient to do that. However, this is not
the only signal required to direct the pollen tube to the ovules; the pollen tube also
follows cues from the stigma and style as it grows towards the ovules, which are
required for its growth before it even reaches the ovule.
Having present what you know from the Arabidopsis ovule and the mature pollen
tube structure, explain what is double fertilisation and which are the products of this fertilisation (and ploidy number).
Double fertilisation is the name given to the simultaneous fusion of one of the sperm
nuclei (from pollen) with the egg cell nucleus, which will give origin to the embryo
(ploidy 2n), and the fusion of the other sperm nucleus (from pollen) with the central
cell nucleus (the diploid product of fused polar nuclei), which will give origin to the
endosperm (ploidy 3n).
If you had a plant (haplotype S1S3) that you crossed to the plants (haplotypes: S1S1, S1S3, S3S3, and S2S2) would you expect any seed set if these plants were gametophytic-self-incompatible? Fill in the blank spaces, (say if you would expect seed set or not, and mention what is the expected genotype of the progeny – within the parenthesis), and justify your options. a) If gametophytic self-incompatible S1S3 x S1S1 Seed set (S3S1) x S1S3 .... x S3S3 .... x S2S2 .... b) And if the the plants were sporophytic self-incompatible? S1S3 x S1S1 No seed set (none) x S1S3 .... x S3S3 .... x S2S2 ....
If the plants are gametophytic self-incompatible, only the cross S1S3 x S1S3 would be not fertile because none of the haplotype alleles is different. In all other cases, at least one of the alleles in the pollen is different from the alleles preset in the egg cell. It is the combination of these different haplotype alleles that will give origin to the progeny. If gametophytic self-incompatible: S1S3 x S1S1 –>Seed set (S3S1); S1S3xS1S3 –> No seed set (none); S1S3 x S3S3 –> Seed set (S1S3); S1S3 x S2S2 –> Seed set
(S1S2, S3S2)
If the plants are sporophytic self-incompatible, only the cross S1S3 x S2S2
would be fertile because none of the haplotype alleles from the male are the same as those of the female. Hence the only viable progeny, from these crosses would be S1S2 and S3S2. If sporophytic self-incompatible: S1S3 x S1S1 –> No seed set (none)
S1S3 x S1S3 –> No seed set (none); S1S3 x S3S3 –>No seed set (none) S1S3 x S2S2 –>
Seed set (S1S2, S3S2)
When the pollen tube enters the ovule via the degenerating synergid, and releases its
content, it encounters a transient structure (the actin corona), which has been formed
in the ovule. What is the function of this structure and how would you try to show if
it is essential, knowing that in some mutant plants more than one embryo is formed?
This structure, the ‘actin corona’ is thought to be the structure responsible for physically directing the two sperm nuclei to their final targets (to fuse to the egg cell nucleus and the central cell nucleus). One way to try to show its function would be by either observing the correlation between coronas around the multi egg cells, and the existence of multi embryo seeds, and/or to identify female infertile mutants that affect the actin corona formation.
Wie unterscheidet sich die Meiose in sexueller und apomiktischer (Diplosporie)
Fortpflanzung?
In sexuellen Arten in der 1. meiotischen Teilung, bei apomikten wird die Reduktion
umgangen (Aposporie).
Wie unterscheidet sich eine apomiktischer Population von einer sexuellen?
Da eine apomiktische Population einen Klon darstellt, findet man keine Segregation von Markern (und phänotypischen Merkmalen) in apomiktischen Populationen. Alle Individuen gleichen der Mutter, das Einkreuzen von anderen Merkmalen ist nicht möglich.
