Highly efficient uptake of ultrafine mesoporous silica nanoparticles with excellent biocompatibility by Liriodendron hybrid suspension cells.

The characteristics of the interactions co-cultures of ultrafine mesoporous silica nanoparticles (MSNs) and the Liriodendron hybrid suspension cells were systematically investigated using laser scanning confocal microscope (LSCM) and scanning electron microscopy (SEM). Using fluorescein isothiocyanate (FITC) labeling, the LSCM observations demonstrated that MSNs (size, 5-15 nm) with attached FITC molecules efficiently penetrated walled plant cells through endocytic pathways, but free FITC could not enter the intact plant cells. The SEM measurements indicated that MSNs readily aggregated on the surface of intact plant cells, and also directly confirmed that MSNs could enter intact plant cells; this was achieved by determining the amount of silicon present. After 24 h of incubation with 1.0 mg mL(-1) of MSNs, the viability of the plant cells was analyzed using fluorescein diacetate staining; the results showed that these cells retained high viability, and no cell death was observed. Interestingly, after the incubation with MSNs, the Liriodendron hybrid suspension cells retained the capability for plant regeneration via somatic embryogenesis. Our results indicate that ultrafine MSNs hold considerable potential as nano-carriers of extracellular molecules, and can be used to investigate in vitro gene-delivery in plant cells.

Probing alignment and phase behavior in intact wood cell walls using 2H NMR spectroscopy.

This study presents the first application of (2)H NMR spectroscopy to quantify lignocellulose matrix orientation, and it demonstrates the ability to separately investigate oriented and unoriented amorphous domains in intact natural plant tissue. Matrix orientation is evaluated using NMR quadrupolar interactions in small deuterated probe molecules absorbed into bulk Liriodendron tulipifera sapwood. Ethylene glycol-d(4) deuterium spectra reveal two distinct amorphous domains, a highly oriented phase in the secondary wall S2 layer and an isotropic domain probably reflecting the compound middle lamella (CML). The oriented and isotropic signal areas exhibit thermally reversible changes, postulated to reflect probe redistribution between the S2 layer and the CML. Preliminary studies on a more powerful wood swelling agent, N,N-dimethylformamide-d(1), are also discussed. This (2)H NMR technique provides a new avenue for analysis and understanding of lignocellulose ultrastructure and promises to create new insights in correlating biomass processing with morphological change.

Monitoring endoplasmic reticulum-to-Golgi traffic of a plant calreticulin by protein glycosylation analysis.

Calreticulin is a ubiquitous and highly conserved Ca(2+)-binding protein that is involved in intracellular Ca(2+) homeostasis and molecular chaperoning in the endoplasmic reticulum (ER). Plant calreticulin, in contrast to its animal counterpart, is often glycosylated: its N-glycans have been shown so far to be of the high-mannose type, typical of ER-resident glycoproteins. During the characterization of calreticulin from vegetative and reproductive tissues of Liriodendron tulipifera L., we gained some biochemical evidence that prompted us to investigate the monosaccharide composition and primary structure of the calreticulin N-glycans isolated from the ovary of this dicotyledon tree. The structures of the components of the N-glycan pool were elucidated by HPLC analysis and exoglycosidase sequencing, and further confirmed by matrix-assisted laser desorption/ionization mass spectrometry. The 16 identified oligosaccharide structures, which consisted of both the high-mannose and complex type, are indicative of calreticulin glycan processing through the ER-to-Golgi pathway up to the medial and trans Golgi stacks. Approximately 45% of calreticulin glycan chains are of the complex type, always containing beta(1,2)-xylose, and approximately a third of these also contain alpha(1,3)-fucose in the core. The most complex glycoform harbors the Lewis-a epitope Gal(beta)1-3[Fuc(alpha)1-4]GlcNAc. Immunolocalization of calreticulin with anti-calreticulin antibodies was consistent with protein transit through the Golgi. Thus, although it contains the tetrapeptide HDEL ER retention signal, the reticuloplasmin calreticulin possesses the competence to transit from the ER compartment to the distal Golgi stacks. The final fate of the protein after its complete maturation is still obscure.

Phloem loading in the tulip tree. Mechanisms and evolutionary implications.

Minor vein ultrastructure and phloem loading were studied in leaves of the tulip tree (Liriodendron tulipifera; Magnoliaceae). Plasmodesmatal frequencies leading into minor vein companion cells are higher than in species known to load via the apoplast. However, these companion cells are not specialized as "intermediary cells" as they are in species in which the best evidence for symplastic phloem loading has been documented. Mesophyll cells plasmolyzed in 600 mM sorbitol, whereas sieve elements and companion cells did not plasmolyze even in 1.2 M sorbitol, indicating that solute accumulates in the phloem against a steep concentration gradient. Both [(14)C]sucrose and (14)C-labeled photo-assimilate accumulated in the minor vein network, as demonstrated by autoradiography. [(14)C]sucrose accumulation was prevented by p-chloromercuribenzenesulfonic acid, an inhibitor of sucrose-proton cotransport from the apoplast. p-Chloromercuribenzenesulfonic acid largely, but not entirely, inhibited exudation of radiolabeled photoassimilate. The evidence is most consistent with the presence of an apoplastic component to phloem loading in this species, contrary to speculation that the more basal members of the angiosperms load by an entirely symplastic mechanism.