BURSTING POLLEN is required to organize the pollen germination plaque and pollen tube tip in Arabidopsis thaliana.

Pollen germination may occur via the so-called germination pores or directly through the pollen wall at the site of contact with the stigma. In this study, we addressed what processes take place during pollen hydration (i.e. before tube emergence), in a species with extra-poral pollen germination, Arabidopsis thaliana. A T-DNA mutant population was screened by segregation distortion analysis. Histological and electron microscopy techniques were applied to examine the wild-type and mutant phenotypes. Within 1 h of the start of pollen hydration, an intine-like structure consisting of cellulose, callose and at least partly de-esterified pectin was formed at the pollen wall. Subsequently, this 'germination plaque' gradually extended and opened up to provide passage for the cytoplasm into the emerging pollen tube. BURSTING POLLEN (BUP) was identified as a gene essential for the correct organization of this plaque and the tip of the pollen tube. BUP encodes a novel Golgi-located glycosyltransferase related to the glycosyltransferase 4 (GT4) subfamily which is conserved throughout the plant kingdom. Extra-poral pollen germination involves the development of a germination plaque and BUP defines the correct plastic-elastic properties of this plaque and the pollen tube tip by affecting pectin synthesis or delivery

Relative expression of B- and C-class genes under control and continuous mild heat conditions (CMH32) in anthers of the tomato cultivar Red setter.

<p>A, expression of the B-class genes <i>TAP3</i>, <i>TM6</i>, <i>TPI</i> and <i>LePI</i> and the C-class genes <i>TAG1</i> and <i>TAGL1</i> in young anthers of 2–3 mm. B, gene expression in mature anthers. Values represent the mean ± SE, with the mean expression in the control condition set to 1. *, significantly different from the control treatment, P<0.05; **, P<0.01; ***, P<0.001.</p

List of primers used in this study.

<p>List of primers used in this study.</p

Cross sections of anthers and pistils from mature flowers of the tomato cultivar Red Setter grown under control and continuous mild heat conditions.

<p>A, overview of anthers grown under control conditions (CT). Scale bar: 300 μm. B, overview of anthers and pistil from CHM32. Scale bar 300 μm. C, transmitting-tissue-like cells from an anther grown under CMH32 (close up of B) on the left, and true stylar transmitting tissue from control conditions on the right. Scale bar 20 μm. D, ovule-like deformation from an anther grown under CMH32 (scale bar 30 μm). Upper inset shows overview of CMH32 anther with ovule-like deformation (scale bar 300 μm), lower inset shows a true ovule from control conditions (scale bar 50 μm). a, anther; l, locule; ov, ovule; ovl, ovule-like structure; st, style; tt, transmitting tissue; ttl, transmitting tissue-like cells; v, vascular bundle.</p

Continous mild heat conditions affect pollen viability and flower deformation simultaneously.

<p>A, Frequency of anther deformations and pollen germination rate of tomato plants (cv. Red Setter) grown under different temperature regimes (CT, CMH32, CMH34). Values represent the mean ± SD, different letters indicate statistically significant differences (per trait, P<0.01). B, Mature flowers of wild-type tomato (cv. Red Setter) from control (CT) and CMH32 conditions. Insets show the adaxial side of the indicated boxed regions. Scale bars: 1 mm and 0,5 mm (insets). a, anther; ovl, ovule-like structures; p, petal; pi, pistil; s, sepal. C, Frequency of anther deformations and pollen germination rate of wild type (WT) tomato plants (cv. Rubicon) and transgenic lines <i>AtGRXS17-3</i> and <i>AtGRXS17-9</i> grown under CMH32. Under control conditions, no anther deformations were observed, and percentage pollen viability was 60 ± 12 (SD), 60 ± 13 and 56 ± 9 for WT, <i>AtGRXS17-3</i> and <i>AtGRXS17-9</i>, respectively (no significant differences between genotypes). Values represent the mean ± SD, different letters indicate statistically significant differences (per trait, P<0.05).</p

Presence of anther deformations, pollen germination rate and pollen number of wild-type Microtom and the <i>TM6</i>–RNAi line under control and CMH30 conditions.

<p>Presence of anther deformations, pollen germination rate and pollen number of wild-type Microtom and the <i>TM6</i>–RNAi line under control and CMH30 conditions.</p