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Molecular evidence that rough endoplasmic reticulum is the site of calreticulin translation in Petunia pollen tubes growing in vitro.

Suwińska A, Lenartowski R, Smoliński DJ, Lenartowska M - Plant Cell Rep. (2015)

Bottom Line: These results seem to support our idea that CRT is translated on ER membrane-bound ribosomes during pollen germination and pollen tube growth.In elongated pollen tubes, we found CRT mainly localized in the subapical zone, where ER and Golgi stacks are abundant.Therefore, we postulate that subapical-localized CRT is involved in pollen tube growth by maintaining the stable tip-focused Ca(2+) gradient and thus modulating local Ca(2+) concentration within the tube cytoplasm.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Developmental Biology, Faculty of Biology and Environment Protection, Nicolaus Copernicus University, Toruń, Poland.

ABSTRACT

Key message: In germinating pollen grains and growing pollen tubes, CRT is translated on ER membrane-bound ribosomes in the regions where its activity is required for stabilization of tip-focused Ca (2+) gradient. Pollen tube growth requires coordination of signaling, exocytosis, and actin cytoskeletal organization. Many of these processes are thought to be controlled by finely tuned regulation of cytoplasmic Ca(2+) in discrete regions of the tube cytoplasm. Most notably, a mechanism must function to maintain a steep gradient of Ca(2+) that exists at the tip of growing pollen tube. Several pieces of evidence point to calreticulin (CRT) as a key Ca(2+)-binding/-buffering protein involved in pollen germination and pollen tube growth. We previously hypothesized that in germinating pollen and growing tubes, CRT is translated on the ribosomes associated with endoplasmic reticulum (ER) in the regions where its activity might be required. In this report, we have addressed this idea by identifying the sites where CRT mRNA, CRT protein, 18S rRNA, and rough ER are localized in Petunia pollen tubes. We observed all four components in the germinal aperture of pollen grains and in subapical regions of elongating tubes. These results seem to support our idea that CRT is translated on ER membrane-bound ribosomes during pollen germination and pollen tube growth. In elongated pollen tubes, we found CRT mainly localized in the subapical zone, where ER and Golgi stacks are abundant. In eukaryotic cells, these organelles serve as mobile intracellular stores of easily releasable Ca(2+), which can be buffered by proteins such as CRT. Therefore, we postulate that subapical-localized CRT is involved in pollen tube growth by maintaining the stable tip-focused Ca(2+) gradient and thus modulating local Ca(2+) concentration within the tube cytoplasm.

No MeSH data available.


Related in: MedlinePlus

The presence of RER cisternae in the regions of Petunia germinating pollen (a–b′) and growing tubes (c–e′) in which accumulation of PhCRT mRNA, CRT protein, and 18S rRNA was revealed. a–a′ the germinal aperture (ga) of germinating pollen, b–b′ inactive aperture (a) of germinating pollen, c–c′ the subapical zone (saz) of the growing pollen tube, d–d′ peripheral distal shank (dsh) of the pollen tube, e–e′ central dsh of the pollen tube. a′, b′, c′, d′, and e′ are the bigger magnifications of marked regions in respective photos. g Golgi stacks, l lipid body, m mitochondria, rer rough ER, sp sporoderm, va vacuole. Bars 1 μm (a–e), 500 nm (a′, c′, e′), and 250 nm (b′, d′)
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Fig5: The presence of RER cisternae in the regions of Petunia germinating pollen (a–b′) and growing tubes (c–e′) in which accumulation of PhCRT mRNA, CRT protein, and 18S rRNA was revealed. a–a′ the germinal aperture (ga) of germinating pollen, b–b′ inactive aperture (a) of germinating pollen, c–c′ the subapical zone (saz) of the growing pollen tube, d–d′ peripheral distal shank (dsh) of the pollen tube, e–e′ central dsh of the pollen tube. a′, b′, c′, d′, and e′ are the bigger magnifications of marked regions in respective photos. g Golgi stacks, l lipid body, m mitochondria, rer rough ER, sp sporoderm, va vacuole. Bars 1 μm (a–e), 500 nm (a′, c′, e′), and 250 nm (b′, d′)

Mentions: The above results led us to propose that the common sites of PhCRT mRNA, CRT, and 18S rRNA localization in germinating pollen and growing pollen tubes are enriched in ER membrane-bound ribosomes. To test this idea, we performed high-resolution electron microscopy on ultrathin longitudinal sections through in vitro cultivated cells. As shown in Fig. 5, we observed RER cisternae in the same regions in which we found accumulation of PhCRT mRNA, CRT protein, and 18S rRNA: the germinal aperture (Fig. 5a, a′) and inactive apertures (Fig. 5b, b′) of germinated pollen; and the subapical zone (Fig. 5c, c′) and the peripheral (Fig. 5d, d′) and central (Fig. 5e, e′) regions of the distal shank of elongated tubes.Fig. 5


Molecular evidence that rough endoplasmic reticulum is the site of calreticulin translation in Petunia pollen tubes growing in vitro.

Suwińska A, Lenartowski R, Smoliński DJ, Lenartowska M - Plant Cell Rep. (2015)

The presence of RER cisternae in the regions of Petunia germinating pollen (a–b′) and growing tubes (c–e′) in which accumulation of PhCRT mRNA, CRT protein, and 18S rRNA was revealed. a–a′ the germinal aperture (ga) of germinating pollen, b–b′ inactive aperture (a) of germinating pollen, c–c′ the subapical zone (saz) of the growing pollen tube, d–d′ peripheral distal shank (dsh) of the pollen tube, e–e′ central dsh of the pollen tube. a′, b′, c′, d′, and e′ are the bigger magnifications of marked regions in respective photos. g Golgi stacks, l lipid body, m mitochondria, rer rough ER, sp sporoderm, va vacuole. Bars 1 μm (a–e), 500 nm (a′, c′, e′), and 250 nm (b′, d′)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Fig5: The presence of RER cisternae in the regions of Petunia germinating pollen (a–b′) and growing tubes (c–e′) in which accumulation of PhCRT mRNA, CRT protein, and 18S rRNA was revealed. a–a′ the germinal aperture (ga) of germinating pollen, b–b′ inactive aperture (a) of germinating pollen, c–c′ the subapical zone (saz) of the growing pollen tube, d–d′ peripheral distal shank (dsh) of the pollen tube, e–e′ central dsh of the pollen tube. a′, b′, c′, d′, and e′ are the bigger magnifications of marked regions in respective photos. g Golgi stacks, l lipid body, m mitochondria, rer rough ER, sp sporoderm, va vacuole. Bars 1 μm (a–e), 500 nm (a′, c′, e′), and 250 nm (b′, d′)
Mentions: The above results led us to propose that the common sites of PhCRT mRNA, CRT, and 18S rRNA localization in germinating pollen and growing pollen tubes are enriched in ER membrane-bound ribosomes. To test this idea, we performed high-resolution electron microscopy on ultrathin longitudinal sections through in vitro cultivated cells. As shown in Fig. 5, we observed RER cisternae in the same regions in which we found accumulation of PhCRT mRNA, CRT protein, and 18S rRNA: the germinal aperture (Fig. 5a, a′) and inactive apertures (Fig. 5b, b′) of germinated pollen; and the subapical zone (Fig. 5c, c′) and the peripheral (Fig. 5d, d′) and central (Fig. 5e, e′) regions of the distal shank of elongated tubes.Fig. 5

Bottom Line: These results seem to support our idea that CRT is translated on ER membrane-bound ribosomes during pollen germination and pollen tube growth.In elongated pollen tubes, we found CRT mainly localized in the subapical zone, where ER and Golgi stacks are abundant.Therefore, we postulate that subapical-localized CRT is involved in pollen tube growth by maintaining the stable tip-focused Ca(2+) gradient and thus modulating local Ca(2+) concentration within the tube cytoplasm.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Developmental Biology, Faculty of Biology and Environment Protection, Nicolaus Copernicus University, Toruń, Poland.

ABSTRACT

Key message: In germinating pollen grains and growing pollen tubes, CRT is translated on ER membrane-bound ribosomes in the regions where its activity is required for stabilization of tip-focused Ca (2+) gradient. Pollen tube growth requires coordination of signaling, exocytosis, and actin cytoskeletal organization. Many of these processes are thought to be controlled by finely tuned regulation of cytoplasmic Ca(2+) in discrete regions of the tube cytoplasm. Most notably, a mechanism must function to maintain a steep gradient of Ca(2+) that exists at the tip of growing pollen tube. Several pieces of evidence point to calreticulin (CRT) as a key Ca(2+)-binding/-buffering protein involved in pollen germination and pollen tube growth. We previously hypothesized that in germinating pollen and growing tubes, CRT is translated on the ribosomes associated with endoplasmic reticulum (ER) in the regions where its activity might be required. In this report, we have addressed this idea by identifying the sites where CRT mRNA, CRT protein, 18S rRNA, and rough ER are localized in Petunia pollen tubes. We observed all four components in the germinal aperture of pollen grains and in subapical regions of elongating tubes. These results seem to support our idea that CRT is translated on ER membrane-bound ribosomes during pollen germination and pollen tube growth. In elongated pollen tubes, we found CRT mainly localized in the subapical zone, where ER and Golgi stacks are abundant. In eukaryotic cells, these organelles serve as mobile intracellular stores of easily releasable Ca(2+), which can be buffered by proteins such as CRT. Therefore, we postulate that subapical-localized CRT is involved in pollen tube growth by maintaining the stable tip-focused Ca(2+) gradient and thus modulating local Ca(2+) concentration within the tube cytoplasm.

No MeSH data available.


Related in: MedlinePlus