Abstract
Summary The developmental changes involved in the alternation of generation represent the major gene‐switching events in the life history of plants. While a large number of genes are common to both sporophyte and gametophyte, many thousand sequences are specifically expressed in each generation; indeed, certain key constituents (e.g. tubulin) are encoded by different genes in each generation, indicating that sporophyte and gametophyte are responding to different evolutionary pressures. Evidence is accumulating that major gene‐switching events in plants, such as flowering, are regulated by complex control systems which ensures that development occurs only in the correct groups of cells at the appropriate time. A similar, or more sophisticated system might thus be expected to regulate alternation of generation. It is not possible to manipulate alternation of generation in a similar fashion to flowering, but study of apparent aberrations of development occurring in nature and in vitro suggests that alternation only occurs in cells which have become competent to receive particular developmental stimuli. Further, in certain cases, competent cells may be switched either into sporophytic or gametophytic developmental pathways depending upon the nature of the stimulus. Acquisition of competence seems to involve isolation of cells from the symplast, some cytoplasmic dedifferentiation, and perhaps cell cycle arrest or transition. The stimuli in vivo appear metabolic in nature, although embryogenesis may be activated by specific classes of glycoproteins. Interestingly, examination of agamospermic systems suggests that fertilization of the egg per se is not the signal which activates sporophytic development. Once competent cells have received the stimulus they start to develop, with no delay in a ‘determined’ state. Sporophytic and gametophytic development in vivo and in vitro both start with an asymmetric division, except for the female gametophyte which may arise via a range of developmental pathways, depending on the species.
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Claims 12
Claim · model-written summary
Many sequences are specifically expressed in either the sporophyte or gametophyte.
- Taxon
- FLOWERING PLANTSMagnoliopsidat0
- Outcome
- many thousand sequences are specifically expressed in each generatione0
Verbatim
t0“FLOWERING PLANTS”
e0“many thousand sequences are specifically expressed in each generation”
Claim · model-written summary
Some constituents, including tubulin, are encoded by different genes in the two generations.
- Taxon
- FLOWERING PLANTSMagnoliopsidat0
- Gene
- tubuline0
- Outcome
- encoded by different genes in each generatione0
Verbatim
t0“FLOWERING PLANTS”
e0“certain key constituents (e.g. tubulin) are encoded by different genes in each generation”
Claim · model-written summary
Evidence suggests flowering gene switching is controlled by complex systems coordinating cell group and timing.
- Taxon
- plantsViridiplantaee0
- Outcome
- development occurs only in the correct groups of cells at the appropriate timee0
- Qualifier
- complex control systemse0
Verbatim
t0“FLOWERING PLANTS”
e0“major gene‐switching events in plants, such as flowering, are regulated by complex control systems which ensures that development occurs only in the correct groups of cells at the appropriate time”
Claim · model-written summary
Alternation of generations appears restricted to cells competent to receive developmental stimuli.
- Taxon
- FLOWERING PLANTSMagnoliopsidat0
- Outcome
- alternation only occurse0
- Qualifier
- cells which have become competent to receive particular developmental stimulie0
Verbatim
t0“FLOWERING PLANTS”
e0“alternation only occurs in cells which have become competent to receive particular developmental stimuli”
Claim · model-written summary
The stimulus can direct competent cells into sporophytic or gametophytic pathways.
- Taxon
- FLOWERING PLANTSMagnoliopsidat0
- Outcome
- sporophytic or gametophytic developmental pathwayse0
- Qualifier
- depending upon the nature of the stimuluse0
Verbatim
t0“FLOWERING PLANTS”
e0“competent cells may be switched either into sporophytic or gametophytic developmental pathways depending upon the nature of the stimulus”
Claim · model-written summary
Competence acquisition appears to involve symplast isolation, cytoplasmic dedifferentiation, and possibly cell-cycle arrest or transition.
- Taxon
- FLOWERING PLANTSMagnoliopsidat0
- Outcome
- Acquisition of competencee0
- Qualifier
- isolation of cells from the symplast, some cytoplasmic dedifferentiation, and perhaps cell cycle arrest or transitione0
Verbatim
t0“FLOWERING PLANTS”
e0“Acquisition of competence seems to involve isolation of cells from the symplast, some cytoplasmic dedifferentiation, and perhaps cell cycle arrest or transition”
Claim · model-written summary
In vivo stimuli for generation switching appear metabolic.
- Taxon
- FLOWERING PLANTSMagnoliopsidat0
- Outcome
- stimuli in vivoe0
- Qualifier
- metabolic in naturee0
Verbatim
t0“FLOWERING PLANTS”
e0“The stimuli in vivo appear metabolic in nature”
Claim · model-written summary
Specific glycoprotein classes may activate embryogenesis.
- Taxon
- FLOWERING PLANTSMagnoliopsidat0
- Gene
- glycoproteinse0
- Outcome
- embryogenesise0
Verbatim
t0“FLOWERING PLANTS”
e0“embryogenesis may be activated by specific classes of glycoproteins”
Claim · model-written summary
Agamospermic systems suggest egg fertilization itself does not activate sporophytic development.
- Taxon
- FLOWERING PLANTSMagnoliopsidat0
- Outcome
- sporophytic developmente0
- Qualifier
- fertilization of the egg per se is not the signale0
Verbatim
t0“FLOWERING PLANTS”
e0“examination of agamospermic systems suggests that fertilization of the egg per se is not the signal which activates sporophytic development”
Claim · model-written summary
Competent cells begin development immediately after receiving the stimulus.
- Taxon
- FLOWERING PLANTSMagnoliopsidat0
- Outcome
- start to develop, with no delay in a ‘determined’ statee0
Verbatim
t0“FLOWERING PLANTS”
e0“Once competent cells have received the stimulus they start to develop, with no delay in a ‘determined’ state”
Claim · model-written summary
Sporophytic and gametophytic development usually begin with asymmetric division.
- Taxon
- FLOWERING PLANTSMagnoliopsidat0
- Outcome
- both start with an asymmetric divisione0
- Qualifier
- except for the female gametophytee0
Verbatim
t0“FLOWERING PLANTS”
e0“Sporophytic and gametophytic development in vivo and in vitro both start with an asymmetric division, except for the female gametophyte”
Claim · model-written summary
Female gametophytes can arise through different developmental pathways depending on species.
- Taxon
- FLOWERING PLANTSMagnoliopsidat0
- Organ / stage
- female gametophytee0
- Outcome
- a range of developmental pathwayse0
- Qualifier
- depending on the speciese0
Verbatim
t0“FLOWERING PLANTS”
e0“the female gametophyte which may arise via a range of developmental pathways, depending on the species”