Female Gametophyte. Male Gametophyte. Ovary and 5 stigma lobes of Sagina nodosa (Knotted Pearlwort, Caryophyllaceae). Note stigmatic papillae. Onagraceae Oenothera fruticosa. Malvaceae Sildalcea malviflora. Liliaceae Lilium auratum. Euphorbiaceae Ricinus communis.
Ovary and 5 stigma lobes of Sagina nodosa (Knotted Pearlwort, Caryophyllaceae). Note stigmatic papillae.
Malvaceae Sildalcea malviflora
Liliaceae Lilium auratum
Euphorbiaceae Ricinus communis
Convovlulaceae Ipomea purpurea
Asteraceae Helianthus annuus
Recognition systems depend on the genetic make up of the pollen and the stigma.
If expressed genes match, pollen grain won’t germinate.
Both parental genes expressed by pollen and by stigma
S1 dominant over S2 in pollen but codoiminant in stigma; S2 and S3 are co- dominant in both
Only S1 (when present) is dominant in pollen and stigma
Pollen Grain -polyporate (with many round pores)
Lonicera canadensis (Caprifoliaceae), Fly-bush honeysuckle, stigma and portion of style. Note numerous germinated pollen grains and the few pollen tubes that are ahead of all the others.
Triploid Endosperm nucleus
Note the egg and central cell
Have incomplete cell walls.
The sperm have no cell walls.
Higashiyama, T. et al. 2001. Pollen Tube Attraction by the Synergid Cell. Science 293:1480-1483.
Torenia fournieri, wishbone flower (note arched stamens) (Scrophulariaceae)
Note the embryo sac (female gametophyte) extends out of the micropylar opening. FA=filiform apparatus.
Ovule with embryo sac
Arrowheads ( ) =micropylar end of embryo sac.
Arrows ( )= pollen tubes
Excised Style Pollen Tubes Ovules
Note the pollen tube (arrow) is attracted to the embryo sac with both synergids even though the egg and central cell have been ablated,
Pollen tubes bypass the embryo sac with 2 ablated synergids (2 triangles)even though the egg and central cell are functional.
This fertilized egg cell could not attract any more pollen tubes even though there was still one functional synergid. Thus fertilization shuts down any remaining signaling from the intact synergid.
Williams & Friedman’s (2002) article on the diploid endosperm made the cover of Nature.
2 Synergids (sy)
1 Egg (e) located behind the synergids (but shown in the inset)
1 nucleus (cc) in the central cell (defined by the dark region below the egg and synergids)
Scale bar, 10 µm.
a. Sperm nucleus approaches
b&c. Sperm engulfed by central cell nucleus
d. The now diploid endosperm begins mitotic division (prophase).
Scale bar, 10 µm.
The question is did the Nymphaeaceae and other “basal” angiosperm families loose the antipodal cells and one of the central cell nuclei?
Or did the other groups gain the antipodals and extra central cell nucleus?
Which is ancestral?
• Either triploid endosperm evolved twice from a diploid condition during the early evolution of angiosperms (a)
•Or diploid endosperm evolved twice from a triploid condition (b).