Male Gametophyte

Female Gametophyte

Ovary and 5 stigma lobes of Sagina nodosa (Knotted Pearlwort, Caryophyllaceae). Note stigmatic papillae.

http://remf.dartmouth.edu/images/botanicalPollenSEM/source/12.html

Malvaceae Sildalcea malviflora

Onagraceae Oenothera fruticosa

Liliaceae Lilium auratum

Convovlulaceae Ipomea purpurea

Euphorbiaceae Ricinus communis

Asteraceae Helianthus annuus

Stigma of Arabidopsis

http://mips.gsf.de/proj/thal/ens/stigma.html

Recognition systems depend on the genetic make up of the pollen and the stigma.

Gametophytic Incompatibility

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

Sporophytic Incompatibility

If expressed genes match, pollen grain won’t germinate.

Pollen Tube

Stigmatic papillae

Pollen Grain -polyporate (with many round pores)

Sagina nodosa (Caryophyllaceae)

Callose Plugs

Ovules

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.

Fertilization

Syngamy

Zygote

Triploid Endosperm nucleus

Note the egg and central cellHave incomplete cell walls. The sperm have no cell walls.

Torenia fournieri, wishbone flower (note arched stamens) (Scrophulariaceae)

Note the embryo sac (female gametophyte) extends out of the micropylar opening. FA=filiform apparatus.

Higashiyama, T. et al. 2001. Pollen Tube Attraction by the Synergid Cell. Science 293:1480-1483.

Torenia pollen tube growth.

Ovule with embryo sac

Arrowheads ( ) =micropylar end of embryo sac.

Arrows ( )= pollen tubes

Excised StylePollen Tubes Ovules

Torenia experiment

Before and after synergid ablation.

Pollen tubes bypass the embryo sac with 2 ablated synergids (2 triangles)even though the egg and central cell are functional.

Note the pollen tube (arrow) is attracted to the embryo sac with both synergids even though the egg and central cell have been ablated,

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.

Four-celled/four-nucleate Nuphar (Nymphaeaceae) female gametophyte.

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.

2nd Fertilization in Nuphar (fusion of the sperm and central cell nuclei)

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 typical 7-celled, 8-nucleated embryo sac is shown in a.

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).

7-celled plesiomorphic

4-celled plesiomorphic