PMC

Effects of B toxicity on cell wall architecture with cellulase treatment. (A) Esterified pectins labeled with JIM7 in control pollen tube treated with cellulase. (B) Esterified pectins in B toxicity-treated pollen tube treated with cellulase. (C) Quantitative analysis of the fluorescent intensity of esterified pectins in the wall of control (Control) and B toxicity treated pollen tubes which were digested with cellulase. (D) Acid pectins indicated by JIM 5 labeling in control pollen tube treated with cellulase. (E) Acid pectins in B toxicity-treated pollen tube treated with cellulase. (F) Quantitative analysis of acid pectins fluorescent intensity in the wall of control pollen tubes (Control) and B toxicity-treated pollen tubes which were digested with cellulase. (G) Cellulose in control pollen tube digested with cellulase indicated by CBM3a labeling. (H) Cellulose in B toxicity-treated pollen tube and then digested with cellulase. (I) Quantitative analysis of the fluorescent intensity of cellulose in the wall of control (Control) and B toxicity-treated pollen tubes that were digested with cellulase. (J) Callose in control pollen tube indicated by monoclonal antibody to (1 → 3)-β-glucan labeling digested with cellulase. (K) Callose in B toxicity-treated pollen tube digested with cellulase. (L) Quantitative analysis of callose fluorescent intensity in the wall of control (Control) and B toxicity-treated pollen tubes that were digested with cellulase. (M) SEM of control pollen tube digested with cellulase. (N) SEM of B toxicity-treated pollen tube digested with cellulase. (O) TEM transverse section of control pollen tube digested with cellulase. The fibrous pectic layer in OW became loosened. (P,Q) TEM transverse section of B toxicity-treated pollen tube digested with cellulase. A small number of fibers were present in OW, but much more fibers were crosslinked with the callose layer. (R) FTIR spectra from the tip regions of C. mollissima pollen tubes digested with cellulase (control pollen tube: Control), B toxicity-treated pollen tubes digested with cellulase and the FTIR differential spectrum (B toxicity–control) generated by digital subtraction of the control spectra from B toxicity-treated spectra digested with cellulase (B toxicity). Bar = 10 μm in (A,B,D,E,G,H,J,K). Bar = 3 μm in M and N; Bar = 2 μm in (O,P). OW, Outer wall; IW, inner wall. The arrows showed the wave morphology (M) and wave protuberances (N).

A hypothetical model for the effects of IAA on pollen tube growth in Torenia fournieri. IAA stimulates the amount and activity of mitochondria and the secretion and fusion of SVs in the pollen tube, which transports more cell wall materials (such as pectin) and various enzymes (such as PM H⁺-ATPase and PME) into the tube tip. The increase in pectin indicates the enhancement of cell wall synthesis. The increased numbers of mitochondria support more energy (ATP) for various cellular activities such as the execution of PM H⁺-ATPase function. The increase in PM H⁺-ATPase results in a change in the pH condition of the cell wall, which may lead to the modification of cell wall architecture. The increase of PME activity stimulates the pectin de-esterification process and consequently causes the alteration in pectin architecture. IAA also induces reorientation of cellulose microfibrils in the tube cell wall, which results in modification of the cell wall architecture. Simultaneous cell wall synthesis enhancement and cell wall architecture modification lead to the promotion of pollen tube growth, accompanied by a narrower tube diameter and a straighter tube.

In vitro pollen tube growth, β-glucan staining, and immunolocalization of Arabidopsis pollen tube wall epitopes. A, Sixteen-hour-old in vitro pollen tubes grown in liquid medium (arrows show callose plugs). The inset is a closeup of a 16-h-old in vitro pollen tube tip. B, Cytochemical staining of β-glucan (callose) with aniline blue showing a callose plug (arrow) and a lack of staining in the pollen tube tip region (arrowhead). C, Cytochemical staining with calcofluor white showing callose plugs (arrows) and the localization of β-glucans in the wall. D to N, Immunofluorescence labeling of cell wall polymer epitopes at the surface of pollen tubes. D to F, Arabidopsis pollen tube wall epitopes probed with anti-pectin MAbs JIM7 (D), JIM5 (E), and LM8 (F), specific for highly and low methylesterified HG and xylogalacturonan, respectively. D, The JIM7 tag showed a strong signal at the tip in a well-developed pollen tube and emerging tube tip from the pollen grain (inset). E, Pollen tube stained with JIM5 showing a very weak intensity of labeling at the tip (arrowhead) compared with the wall back from the tip. F, LM8 labeled evenly the entire pollen tube wall. The insert is a closeup of an in vitro pollen tube tip. G to J, Detection of (1→5)-α-l-arabinan epitopes with LM6 (G and H) and LM13 (I and J). Labeling was evenly distributed along the entire tube wall, with a strong signal at the pollen tube tip. Note a collar-like structure (asterisk) labeled at the emergence of the pollen tube from the pollen grain in G. K and L, Immunofluorescence staining of the nongalactosylated (XXXG motif) and fucosylated XyG with LM15 (K) and CCRC-M1 (L), respectively. Labeling with both MAbs was not evenly detected in the wall and displayed periodic deposition of the epitopes containing polysaccharides during pollen tube growth. M and N, LM2, which recognizes β-d-GlcpUA-(1→3)-α-d-GalpUA-(1→2)-l-Rha moieties of AGPs, labeled weakly the whole tube, with the strongest signal at the tip. In M, a more intense labeling (asterisk) was observed at the emergence of the tube from the pollen grain. Pollen tubes were grown for 6 h except in A and C (16 h). pg, Pollen grain. Bars = 50 μm (A–C) and 5 μm (A inset and D–N).

Schematic model of NbSWP9 functions in polar tube anchoring to the spore wall and during the process of N. bombycis germination. (A) NbSWP9 interacts with polar tube proteins and is localized primarily in the polar tube and spore wall of N. bombycis. The polar tube is formed and scattered in the sporoplasm. Moreover, NbSWP7 is distributed mainly in the interior of the sporoblast (see also and ). (B) Subsequently, with sporoblasts being transformed into mature spores, the disordered polar tube turns in an orderly orientation and is anchored to the spore wall by the scaffolding protein NbSWP9 (see also ). (C) During the spore germination process, NbSWP9 and the polar tube are discharged, and the sporoplasm was released under a suitable stimulus. The majority of NbSWP9 accumulated in the end-terminal part of the extruded polar tube and anchoring disk to mediate the anchoring and attachment of the discharged polar tube to the spore wall. Therefore, NbSWP9 is involved in the process of spore germination (see also to ).