The first case of actinide triple helices: pH-dependent structural evolution and kinetically-controlled transformation of two supramolecular conformational isomers.

The first actinide triple helices, including two supramolecular conformational isomers of uranium(VI), have been synthesized with the aid of a flexible V-shaped ligand and a rigid aromatic base. The isomers exhibit an intriguing pH-dependent structural evolution and a kinetically-controlled transformation via a novel conformational rearrangement of the organic base.

Preliminary enrichment and separation of chlorogenic acid from Helianthus tuberosus L. leaves extract by macroporous resins.

In the present study, a simple and efficient method for the preparative separation of 3-CQA from the extract of Helianthus tuberosus leaves with macroporous resins was studied. ADS-21 showed much higher adsorption capacity and better adsorption/desorption properties for 3-CQA among the tested resins. The adsorption of 3-CQA on ADS-21 resin at 25°C was fitted best to the Langmuir isotherm model and pseudo-second-order kinetic model. Dynamic adsorption/desorption experiments were carried out in a glass column packed with ADS-21 to optimise the separation process of 3-CQA from H. tuberosus leaves extract. After one treatment with ADS-21, the content of 3-CQA in the product was increased 5.42-fold, from 12.0% to 65.2%, with a recovery yield of 89.4%. The results demonstrated that the method was suitable for large-scale separation and manufacture of 3-CQA from H. tuberosus leaves.

The ARID-HMG DNA-binding protein AtHMGB15 is required for pollen tube growth in Arabidopsis thaliana.

In flowering plants, male gametes (sperm cells) develop within male gametophytes (pollen grains) and are delivered to female gametes for double fertilization by pollen tubes. Therefore, pollen tube growth is crucial for reproduction. The mechanisms that control pollen tube growth remain poorly understood. In this study, we demonstrated that the ARID-HMG DNA-binding protein AtHMGB15 plays an important role in pollen tube growth. This protein is preferentially expressed in pollen grains and pollen tubes and is localized in the vegetative nuclei of the tricellular pollen grains and pollen tubes. Knocking down AtHMGB15 expression via a Ds insertion caused retarded pollen tube growth, leading to a significant reduction in the seed set. The athmgb15-1 mutation affected the expression of 1686 genes in mature pollen, including those involved in cell wall formation and modification, cell signaling and cellular transport during pollen tube growth. In addition, it was observed that AtHMGB15 binds to DNA in vitro and interacts with the transcription factors AGL66 and AGL104, which are required for pollen maturation and pollen tube growth. These results suggest that AtHMGB15 functions in pollen tube growth through the regulation of gene expression.

Two new flavonoid glycosides from the halophyte Limonium franchetii.

Two new flavonoid glycosides, named quercetin-3-O-(2″-O-tigloyl)-α-L-rhamnopyranoside (1) and quercetin-3-O-(3″-O-tigloyl)-α-L-rhamnopyranoside (2), together with 10 known flavonoids (3-12), were isolated from the whole plant of the halophyte Limonium franchetii. Their structures were elucidated on the basis of extensive spectroscopic analysis including 2D NMR and HR-EI-MS. In addition, primary bioassays showed that compound 1 had moderate cytotoxic activity against rat C6 glioma cell lines.

Flavonoids from the halophyte Apocynum venetum and their antifouling activities against marine biofilm-derived bacteria.

Eleven flavonoids were isolated from the leaves of the halophyte Apocynum venetum. Among them, the isolation of plumbocatechin A (1), 8-O-methylretusin (2) and kaempferol 3-O-(6″-O-acetyl)-ß-D-galactopyranoside (7) was reported for the first time from this plant. Their structures were identified by using spectral methods, including 2D NMR experiments, and confirmed by comparing with the literature data. In addition, the antifouling activities of these compounds against the marine fouling bacteria, Bacillus thuringiensis, Pseudoalteromonas elyakovii and Pseudomonas aeruginosa, have been evaluated in this article.

Male gametophyte defective 4 encodes a rhamnogalacturonan II xylosyltransferase and is important for growth of pollen tubes and roots in Arabidopsis.

In flowering plants, the growth of pollen tubes is essential for the delivery of sperm to the egg cells. Although many factors (including cell-wall properties) are involved in this process, little is known about the underlying molecular mechanisms that regulate the growth of pollen tubes. We report here the characterization of an Arabidopsis mutant male gametophyte defective 4 (mgp4) that is severely defective in pollen tube growth. The mgp4 mutation also impairs root growth of pollen-rescued mgp4 mutant plants generated by expressing MGP4 cDNA under the control of a pollen grain/tube-specific promoter. The MGP4 gene encodes a putative xylosyltransferase and is expressed in many organs/tissues, including pollen tubes and roots. MGP4 protein expressed in Pichia pastoris exhibited xylosyltransferase activity and transferred d-xylose onto l-fucose. The pectic polysaccharide rhamnogalacturonan II (RG-II), isolated from 7-day-old pollen-rescued mutant seedlings, exhibited a 30% reduction in 2-O-methyl d-xylose residues. Furthermore, an exogenous supply of boric acid enhanced RG-II dimer formation and partially restored the root growth of the pollen-rescued mutant seedlings. Taken together, these results suggest that MGP4 plays important roles in pollen tube and root growth by acting as a xylosyltransferase involved in the biosynthesis of pectic RG-II.

MALE GAMETOPHYTE DEFECTIVE 2, encoding a sialyltransferase-like protein, is required for normal pollen germination and pollen tube growth in Arabidopsis.

Sialyltransferases (SiaTs) exist widely in vertebrates and play important roles in a variety of biological processes. In plants, several genes have also been identified to encode the proteins that share homology with the vertebrate SiaTs. However, very little is known about their functions in plants. Here we report the identification and characterization of a novel Arabidopsis gene, MALE GAMETOPHYTE DEFECTIVE 2 (MGP2) that encodes a sialyltransferase-like protein. MGP2 was expressed in all tissues including pollen grains and pollen tubes. The MGP2 protein was targeted to Golgi apparatus. Knockout of MGP2 significantly inhibited the pollen germination and retarded pollen tube growth in vitro and in vivo, but did not affect female gametophytic functions. These results suggest that the sialyltransferase-like protein MGP2 is important for normal pollen germination and pollen tube growth, giving a novel insight into the biological roles of the sialyltransferase-like proteins in plants.

The Arabidopsis eukaryotic translation initiation factor 3, subunit F (AteIF3f), is required for pollen germination and embryogenesis.

Previous studies have shown that subunits E (eIF3e), F (eIF3f) and H (elF3h) of eukaryotic translation initiation factor 3 play important roles in cell development in humans and yeast. eIF3e and eIF3h have also been reported to be important for normal cell growth in Arabidopsis. However, the functions of subunit eIF3f remain largely unknown in plant species. Here we report characterization of mutants for the Arabidopsis eIF3f (AteIF3f) gene. AteIF3f encodes a protein that is highly expressed in pollen grains, developing embryos and root tips, and interacts with Arabidopsis eIF3e and eIF3h proteins. A Ds insertional mutation in AteIF3f disrupted pollen germination and embryo development. Expression of some of the genes that are essential for pollen tube growth and embryogenesis is down-regulated in ateif3f-1 homozygous seedlings obtained by pollen rescue. These results suggested that AteIF3f might play important roles in Arabidopsis cell growth and differentiation in combination with eIF3e and eIF3h.

MALE GAMETOPHYTE DEFECTIVE 1, encoding the FAd subunit of mitochondrial F1F0-ATP synthase, is essential for pollen formation in Arabidopsis thaliana.

In flowering plants, pollen formation is a complex process and strictly controlled by genetic factors. Although thousands of genes have been identified to be highly or specifically expressed in pollen grains, little is known about the functions and regulatory mechanisms of the genes in pollen formation. Here we report the characterization of a novel gene, MALE GAMETOPHYTE DEFECTIVE 1 (MGP1), that is essential for pollen formation in Arabidopsis thaliana. MGP1 encodes the F(A)d subunit of mitochondrial F(1)F(0)-ATP synthase in Arabidopsis. It was highly expressed in pollen grains at the later developmental stage. Mutation in MGP1 led to destruction of the mitochondria in pollen grains at the dehydration stage and subsequently death of the pollen grains. These results suggested that MGP1 plays important roles in pollen formation, possibly by regulating the activity of mitochondrial F(1)F(0)-ATP synthase in Arabidopsis pollen grains.