Differentiating sieve elements in the phloem of angiosperms produce abundant phloem-specific proteins before their protein synthesis machinery is degraded. These P-proteins initially form dense bodies, which disperse into individual filaments when the sieve element matures. In some cases, however, the dense protein agglomerations remain intact and are visible in functional sieve tubes as non-dispersive P-protein bodies, or NPBs. Species exhibiting NPBs are distributed across the entire angiosperm clade. We found that NPBs in the model tree,
- NSF-PAR ID:
- 10056684
- Publisher / Repository:
- PeerJ
- Date Published:
- Journal Name:
- PeerJ
- Volume:
- 6
- ISSN:
- 2167-8359
- Page Range / eLocation ID:
- Article No. e4665
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Symplasmicly connected cells called sieve elements form a network of tubes in the phloem of vascular plants. Sieve elements have essential functions as they provide routes for photoassimilate distribution, the exchange of developmental signals, and the coordination of defense responses. Nonetheless, they are the least understood main type of plant cells. They are extremely sensitive, possess a reduced endomembrane system without Golgi apparatus, and lack nuclei and translation machineries, so that transcriptomics and similar techniques cannot be applied. Moreover, the analysis of phloem exudates as a proxy for sieve element composition is marred by methodological problems. We developed a simple protocol for the isolation of sieve elements from leaves and stems of Nicotiana tabacum at sufficient amounts for large-scale proteome analysis. By quantifying the enrichment of individual proteins in purified sieve element relative to bulk phloem preparations, proteins of increased likelyhood to function specifically in sieve elements were identified. To evaluate the validity of this approach, yellow fluorescent protein constructs of genes encoding three of the candidate proteins were expressed in plants. Tagged proteins occurred exclusively in sieve elements. Two of them, a putative cytochrome b561/ferric reductase and a reticulon-like protein, appeared restricted to segments of the endoplasmic reticulum (ER) that were inaccessible to green fluorescent protein dissolved in the ER lumen, suggesting a previously unknown differentiation of the endomembrane system in sieve elements. Evidently, our list of promising candidate proteins ( SI Appendix , Table S1 ) provides a valuable exploratory tool for sieve element biology.more » « less
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Premise The dimensions of phloem sieve elements have been shown to vary as a function of tree height, decreasing hydraulic resistance as the transport pathway lengthens. However, little is known about ontogenetic patterns of sieve element scaling. Here we examine within a single species (
Quercus rubra ) how decreases in hydraulic resistance with distance from the plant apex are mediated by overall plant size.Methods We sampled and imaged phloem tissue at multiple heights along the main stem and in the live crown of four size classes of trees using fluorescence and scanning electron microscopy. Sieve element length and radius, the number of sieve areas per compound plate, pore number, and pore radius were used to calculate total hydraulic resistance at each sampling location.
Results Sieve element length varied with tree size, while sieve element radius, sieve pore radius, and the number of sieve areas per compound plate varied with sampling position. When data from all size classes were aggregated, all four variables followed a power‐law trend with distance from the top of the tree. The net effect of these ontogenetic scalings was to make total hydraulic sieve tube resistance independent of tree height from 0.5 to over 20 m.
Conclusions Sieve element development responded to two pieces of information, tree size and distance from the apex, in a manner that conserved total sieve tube resistance across size classes. A further differentiated response between the phloem in the live crown and in the main stem is also suggested.
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Chi Fru, Ernest ; Chik, Alex ; Colwell, Fredrick ; Dittrich, Maria ; Engel, Annette ; Keenan, Sarah ; Meckenstock, Rainer ; Omelon, Christopher ; Purkamo, Lotta ; Weisener, Chris (Ed.)
Roots are common features in basaltic lava tube caves on the island of Hawai‘i. For the past 50 years, new species of cave-adapted invertebrates, including cixiid planthoppers, crickets, thread-legged bugs, and spiders, have been discovered from root patches in lava tubes on different volcanoes and across variable climatic conditions. Assessing vegetation on the surface above lava tube passages, as well as genetic characterization of roots from within lava tubes, suggest that most roots belong to the native pioneer tree, ‘ōhi‘a lehua (
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The gene encoding the cyanobacterial ferritin
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SUMMARY Pollen tubes (PTs) grow by the targeted secretion of new cell wall material to their expanding tip region. Sec1/Munc18 (SM) proteins promote membrane fusion through regulation of the SNARE complex. We have previously shown that disruption of protein glycosylation in the
Arabidopsis thaliana hpat1 hpat3 double mutant leads to PT growth defects that can be suppressed by reducing secretion. Here, we identified five point mutant alleles of the SM proteinSEC1A ashpat1/3 suppressors. The suppressors increased seed set, reduced PT growth defects and reduced the rate of glycoprotein secretion. In the absence of thehpat mutations,sec1a reduced pollen germination and PT elongation producing shorter and wider PTs. Consistent with a defect in membrane fusion,sec1a PTs accumulated secretory vesicles. Thoughsec1a had significantly reduced male transmission, homozygoussec1a plants maintained full seed set, demonstrating thatSEC1A was ultimately dispensable for pollen fertility. However, when combined with a mutation in anotherSEC1 ‐likeSM gene,keule , pollen fertility was totally abolished. Mutation insec1b , the final member of the Arabidopsis SEC1 clade, did not enhance thesec1a phenotype. Thus, SEC1A is the major SM protein promoting pollen germination and tube elongation, but in its absence KEULE can partially supply this activity. When we examined the expression of the SM protein family in other species for which pollen expression data were available, we found that at least one Sec1‐like protein was highly expressed in pollen samples, suggesting a conserved role in pollen fertility in other species.