Immunocytochemical localisation of actin and profilin in the generative cell of angiosperm pollen: TEM studies on high-pressure frozen and freeze-substitutedLedebouria socialis Roth (Hyacinthaceae)

Abstract

Actin was demonstrated for the first time at the EM level in the generative cell of mature angiosperm pollen by using immuno-gold labelling of high-pressure frozen and freeze-substituted Ledebouria socialis Roth anthers. In addition, profilin, an actin-monomer binding protein, is shown to coexist in the generative cell. We attribute the detection of actin and profilin to the applied cryomethods which yield a much better preservation of ultrastructure and antigenicity of delicate cytoskeletal constituents than conventional fixation techniques. Actin labelling was observed within the cytoplasm of the generative cell and became especially clear in close vicinity to microtubular bundles. Filamentous structures congruent with the actin labelling patterns do occur, but are not a frequent feature. Profilin was localised throughout the cytoplasm.

Profilin is localized in the nucleus-associated microtubule and actin system and is evenly distributed in the cytoplasm of the green algaMicrasterias denticulata

“…Profilin detection in the nucleus associated with the nucleolus, heterochromatin, and the nuclear pores of M. denticulata is consistent with ultrastructural observations on pollen tubes (Hess and Valenta 1997) and with earlier investigations of M. denticulata where microinjecting fluorescently labeled profilin into developing cells revealed a marked staining of the nucleus (Holzinger et al 1997). It is known that several natural ligands for profilin such as phosphoinositides (Mazzotti et al 1995) or proline-rich proteins (Alevizopoulos et al 1995) are located in the nucleus and the function of some profilin isoforms are closely related to interaction with proline-rich motives .…”

“…Therefor we have used immunogold electron microscopy for profilin detection in M. denticulata. In plants, so far profilin has been localized by immunoelectron microscopy only in pollen (Grote et al , 1995Vrtala et al 1993;Hess et al 1995;Hess and Valenta 1997;Vidali and Hepler 1997;von Witsch et al 1998;Grote 1999), and there are only a few reports in other organisms (e.g., Bubb et al 1998).…”

Pollen Profilin Function Depends on Interaction with Proline-Rich Motifs

“…Multiple isoforms of profilin are expressed in the pollen of many species, which raises the question whether these are functionally redundant or whether they perform unique functions. The intracellular distribution of profilin in pollen from several different plant species has been investigated by using immunocytochemical analyses (Grote et al, 1993(Grote et al, , 1995Hess et al, 1995;Vidali and Hepler, 1997) and the microinjection of fluorescent profilin analogs (Vidali and Hepler, 1997). The results of these studies indicate that profilin is distributed uniformly in the vegetative cell cytoplasm and pollen tube, and suggest that the multiple isoforms are functionally similar.…”

“…Currently available data demonstrate that profilin is uniformly distributed throughout the vegetative cell and pollen tube (Grote et al, 1993(Grote et al, , 1995Hess et al, 1995;Vidali and Hepler, 1997). However, the possibility that specific components of the heterogeneous profilin population may not be detected without isoformspecific probes has not been adequately addressed.…”

Differential Immune-Reactivity and Subcellular Distribution Reveal the Multifunctional Character of Profilin in Pollen as Major Effect of Sequences Polymorphism

“…Supporting this idea, it has been proposed that plant profilin family multi-functionality might be inferred by natural variation through profilin isovariants Several locations have been attributed to profilin. They have been localized in different plant cells and tissues, including the microspores, pollen grains and pollen tubes (Grote et al 1993(Grote et al , 1995Hess et al 1995;Fischer et al 1996;Vidali & Hepler 1997;Kandasamy 2002). Plant profilin was reported to be localized in the cytoplasm of pollen tube uniformly (Hess et al 1995;Vidali & Hepler 1997).…”