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LETTER TO THE EDITOR

Response to Rogers Letter

Heidelberg Institute of Plant Sciences
University of Heidelberg
69120 Heidelberg, Germany

By reinvestigating the root tips used by Paris et al. (1996), our original intention was to obtain evidence in support of the multivacuole hypothesis and also to see if we could detect by immunogold EM different types of vesicular carriers. As reported in Olbrich et al. (2007), we failed in both instances. However, this does not mean that we have deserted the multivacuole hypothesis to which we have made significant contributions in the past, most recently Hinz et al. (2007).

In his letter, Rogers criticizes the use of immunogold EM as being inadequate to faithfully detect different TIP isoforms, and "that glutaraldehyde fixation might alter the protein epitopes available to the antipeptide antibodies" (see above). This is difficult to assess, but we point out that (1) our fixation protocol (1.5% formaldehyde + 0.25% glutaraldehyde for 15 h) was similar to that used by Paris et al. (1996): 3.75% formaldehyde for 24 h; (2) our data were obtained with various types of TIP antisera and not just the antipeptide antibodies of the Rogers group; and (3) clear differences in the density of immunogold labeling for -TIP and -TIP exist between cells emerging from the meristem and in vacuoles present in cells toward the elongation zones. Admittedly, the staining for -TIP in cells near the meristem was always more prominent than for -TIP, but this is in agreement with figure 3 from Paris et al. (1996), who themselves show that -TIP is virtually absent from the meristem and stele in pea root tips. Although recognizing the reservations that Rogers may have, we were unable to detect a vacuole in cells surrounding the meristem that did not label with both TIP antisera.

Like Hunter et al. (2007), we have also not been able to detect the presence of -TIP in cells of developing Arabidopsis embryos. However, we have recently been able to visualize in the electron microscope a sequence of events similar to that which we previously documented (Hoh et al., 1995) for developing pea cotyledons: PSVs developing de novo and supplanting a preexisting population of lytic-type vacuoles. Thus, the multivacuole hypothesis is far from being declared null; it is just its generality that is being questioned.

	FOOTNOTES

 
www.plantphysiol.org/cgi/doi/10.1104/pp.104.900249

david.robinson{at}urz.uni-heidelberg.de

	LITERATURE CITED

TOP LITERATURE CITED

 
Hinz G, Colanesi S, Hillmer S, Rogers JC, Robinson FG (2007) Localization of vacuolar transport receptors and cargo proteins in the Golgi apparatus of developing Arabidopsis embryos. Traffic 8: 1452–1464[CrossRef][Web of Science][Medline]

Hoh B, Hinz G, Jeong B-K, Robinson DG (1995) Protein storage vacuoles form de novo during pea cotyledon development. J Cell Sci 108: 299–310[Abstract]

Hunter PR, Craddock CP, Di Benedetto S, Roberts LM, Frigerio L (2007) Fluorescent reporter proteins for the tonoplast and the vacuolar lumen identify a single vacuolar compartment in Arabidopsis cells. Plant Physiol 145: 1371–1382[Abstract/Free Full Text]

Olbrich A, Hillmer S, Hinz G, Oliviusson P, Robinson DG (2007) Newly formed vacuoles in root meristems of barley and pea seedlings have characteristics of both protein storage and lytic vacuoles. Plant Physiol 145: 1383–1394[Abstract/Free Full Text]

Paris N, Stanley CM, Jones RL, Rogers JC (1996) Plant cells contain two functionally distinct vacuoles. Cell 85: 563–572[CrossRef][Web of Science][Medline]

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