Programmed Cell Death PCD in Pollen is Triggered by SI

PCD is a highly conserved process used to remove unwanted cells in eu-karyotes. Possible examples of PCD induced by external stimuli have been reported in plants (van Doorn and Woltering 2005). Several classic PCD markers have been identified in plant systems (Danon et al. 2000) and were used to investigate whether PCD is involved in the SI response in incompatible Papaver pollen tubes. DNA fragmentation is a common marker for PCD and, in animal cells, involves activation of caspase-3. Caspases...

One Choice or Two for Organelle Movement

What can we learn from these few reports The massive transport of organelles in plants (designated as cytoplasmic streaming) is supposed to occur on actin filaments and to be dependent on myosins (Chapter VII). Recent advances on the study of organelle transport in plant cells have made use of modern technologies to dissect all the molecular components that take part into the process. The movement of plant cell organelles along actin filaments is now clearly established the photorelocation of...

Identifying Transporter Genes Specific to Pollen in Arabidopsis

To identify transporter genes expressed in pollen, Bock et al. (2006) compiled a list of all known and predicted transporters from the Arabidopsis thaliana genome. Transport proteins are highly conserved from bacteria to eukaryotes Table 1 Partial list of transporter genes that are specifically (S) or preferentially (P) expressed in male gametophyte. The pollen transcriptome from 4 stages of development (Honys and Twell 2004) was compared with transcriptome data of 12 sporophytic tissues. MaxPo...

Ion Gradients and Fluxes

An exciting and compelling result that emerges from the use of ratiometric indicator dyes is the presence of a striking tip-focused gradient in Ca2+ activity that is located in the apical domain of the growing pollen tube, immediately adjacent to the region of maximal elongation (Rathore et al. 1991 Miller et al. 1992) (Fig. 1a). Studies with fura-2-dextran indicate that the gradient extends from 3 M at the extreme apex of the tube to a basal level of 0.17 M within 20 m of the apex (Pierson et...

Gametophytic Mutants Affecting Pollen Development

Mutants affecting pollen development provide excellent material to analyze processes of cell fate specification and cellular function (Sects. 2.1.12.1.4). There have been three major screening strategies to isolate gametophytic mutants and genes affecting pollen development in Arabidopsis gametophyte-targeted forward genetic screens, gametophyte-directed reverse genetic screens and non-gametophyte-directed reverse genetic screens. Male gametophyte-targeted forward genetic screens have...

Cytoskeleton and Motile Processes

The cytoskeleton, especially that composed of actin, plays a crucial role in the control of pollen tube growth. Actomyosin is responsible for driving cytoplas-mic streaming, and the transport of the secretory vesicles to the apical domain. But separate from its role in streaming, actin polymerization turnover in the apical domain is required for pollen tube growth (Gibbon et al. 1999 Vidali et al. 2001 chapter by Yokota and Shimmen, this volume). Thus, agents that block polymerization or...

Expression Analysis of the Phosphoinositide Pathway in Pollen

Recent studies reported unique characteristics of the pollen transcriptome emphasizing a functional skew of pollen transcriptome toward vesicle traf ficking, cytoskeleton and signalling (Twell, Oh and Honys, this volume). Using publicly available expression data, we attempted a more detailed analysis of the expression of genes putatively involved in generation and transduction of PPI signalling. We selected 176 genes, from which 158 were found on Affymetrix ATH1 chip. These included...

Actin Dynamics in Pollen Tubes

Several recent studies have revealed that pollen tube growth depends not only on the presence of stable actin bundles for cytoplasmic streaming, but also on the dynamic state of actin in the tip region. Actin depolymerizing drugs, la-trunculin B and cytochalasin D (Gibbon et al. 1999 Vidali et al. 2001), and G-actin binding proteins, profilin and DNase I (Vidali et al. 2001) microin-jected into pollen, inhibited pollen tube growth at concentrations lower than those needed to suppress the...

Transmission Defect of a Marker

As direct visual screens were proved not appropriate to score for pollen tube growth mutations, alternative strategies have been designed, relying on the fact that gametophytic mutations affect pollen and or embryo sac viability and function, and are therefore not transmitted to the self progeny by the mutated gametophyte. This leads to a segregation distortion for any trait linked to the mutation. If the mutation is linked to a reporter gene (e.g., resistance gene) brought through...

Culture Media and Conditions for Pollen Tube Growth in Vitro

To date, various culture media for in vitro pollen tube culture have been developed some of these are summarised in Table 3. The medium of Brew-baker and Kwack 1963 is one of the most popular for pollen tube culture. Brewbaker and Kwack 1963 tested the pollen of several hundred species, particularly that of petunia and Ornithogalum virens Liliaceae , to determine a basal medium Table 3 . The media of Hodgkin 1983 , Jahnen et al. 1989 and Read et al. 1993 are also popular and have been used as...

Comparison of Fundamental Characteristics of Biological Models

Stigma Pollen Interaction Medicago

Table 2 shows the fundamental characteristics of biological models used in the study of pollen tube growth. Arabidopsis thaliana is now the most commonly used model plant. This species has many characteristics that are useful in the study of reproductive processes. In addition to the availability of molecular genetic tools for Ara-bidopsis, its small, simple pistil is useful for the observation of entire path of growth of a pollen tube Hulskamp et al. 1995 . In vitro culture of the pollen tube...

Pollen Tube Guidance Comprises Multiple Steps and Requires Multiple Signals

A series of genetic experiments in Arabidopsis showed that tube guidance is a multiphase process in which early stages are controlled by sporophytic cells of the stigma, style, and transmitting tissue and the final stages are controlled by the female gametophyte. These experiments also provide critical support for a chemotropic component for tube guidance because some of the mutants analyzed do not disrupt floral architecture but disrupt tube guidance. Pollen tube growth in Arabidopsis has been...

Check and Balance Between RIC3 and RIC4 Pathways Roles in Actin Dynamics

As discussed above, active ROP 1 stimulates two important downstream pathways, the assembly of tip-localized F-actin and the tip-focused Ca2 c gradient, via two distinct mediators, RIC3 and RIC4 Gu et al. 2005 see Fig. 3 . The assembly of tip-localized F-actin could provide forces for targeted delivery and accumulation of secretory vesicles to the future growth site too much and less dynamic F-actin could be the physical barrier to vesicle fusion Giner et al. 2005 . Cytosolic Ca2 is also...