Figure 2.

Altered Expression of MAP18 Interferes with Pollen Tube Growth and Fertilization of Embryos.

(A) to (C) Pollen grains from Arabidopsis wild-type Col (A), map18 mutants (B), and MAP18 OX (C) were used to self-pollinate stigmata. Grains were then incubated for 2 h before fixation and staining with aniline blue. Pollen tubes from each line penetrated the stigmatic tissue similarly and reached the top of the transmitting tracts. Arrows indicate pollen tubes in transmitting tracts.

(D) to (F) Following 24 h incubation, wild-type Col (D), map18 mutants (E), and MAP18 OX (F) pollen tubes all reached the bottom of the transmitting tracts and had grown toward ovules.

(D) Wild-type pollen tubes grew along the funiculus and directly toward the ovule.

(E) The map18 pollen tubes elongated markedly outward from the transmitting tract (closed arrowhead).

(F) MAP18 OX pollen tubes exhibited disordered and entangled patterns in the transmitting tract with some pollen tubes failing to target to ovules (open arrowhead). Bar in (F) = 200 μm for (A) to (F).

(G) Pollen grains from wild-type Col and map18 were used to pollinate self or nonself stigmata. The self-pollinated map18 pollen tubes exhibit meandering growth patterns around the micropyles, but no defect is observed when map18 pistils are pollinated with wild-type pollen.

(H) Pollen grains from wild-type Col and MAP18 OX were used for self or nonself pollination. The self-pollinated MAP18 OX pollen tubes exhibit wandering growth characteristics around the micropyles. These defects are not observed when MAP18 OX pistils are pollinated with wild-type pollen. Bar in (H) = 100 μm for (G) and (H).

(I) Inset indicates a diagram for calculation of the relative distance ratio. Red line indicates the actual path that the pollen tube takes from transmitting tract to micropyle. Green line indicates the direct distance between transmitting tract and micropyle. The ratio of red line length to green line length gives the relative distance ratio. The relative distance ratios of map18 and MAP18 OX pollen tubes are significantly greater than those of wild-type pollen tubes. Error bars indicate ± sd. ***P < 0.001, by Student’s t test.

(J) Significant seed gaps are observed in the siliques of map18 mutants and MAP18 OX. This defect is complemented in COM#1 using wild-type Col for comparison. Bar = 1 mm.

(K) Fertilized (green and mature) and aborted unfertilized (thin and barren; asterisks) ovules in dissected siliques. The complementation construct was able to rescue the abortion phenotype in COM#1. Bar = 0.5 mm.

(L) Seed setting rates were analyzed for wild-type, COM#1, map18, and MAP18 OX siliques. The seed setting rates for both map18 and MAP18 OX were significantly lower than those of wild-type specimens. No significant difference was detected between wild-type and COM#1 seed setting rates. Error bars indicate ± sd. **P < 0.01, by Student’s t test.