Pollen Tube Growth： a Delicate Equilibrium Between Secretory and Endocytic Pathways

Although pollen tube growth is a prerequisite for higher plant fertilization and seed production, the processes leading to pollen tube emission and elongation are crucial for understanding the basic mechanisms of tip growth. It was generally accepted that pollen tube elongation occurs by accumulation and fusion of Golgi-derived secretory vesicles （SVs） in the apical region, or clear zone, where they were thought to fuse with a restricted area of the apical plasma membrane （PM）, defining the apical growth domain. Fusion of SVs at the tip reverses outside cell wall material and provides new segments of PM. However, electron microscopy studies have clearly shown that the PM incorporated at the tip greatly exceeds elongation and a mechanism of PM retrieval was already postulated in the mid-nineteenth century. Recent studies on endocytosis during pollen tube growth showed that different endocytic pathways occurred in distinct zones of the tube, including the apex, and led to a new hypothesis to explain vesicle accumulation at the tip; namely, that endocytic vesicles contribute substantially to V-shaped vesicle accumulation in addition to SVs and that exocytosis does not involve the entire apical domain. New insights suggested the intriguing hypothesis that modulation between exo- and endocytosis in the apex contributes to maintain PM polarity in terms of lipid/protein composition and showed distinct degradation pathways that could have different functions in the physiology of the cell. Pollen tube growth in vivo is closely regulated by interaction with style molecules. The study of endocytosis and membrane recycling in pollen tubes opens new perspectives to studying pollen tube-style interactions in vivo.     

Arabidopsis Thylakoid Formation 1 Is a Critical Regulator for Dynamics of PSII-LHCII Complexes in Leaf Senescence and Excess Light

In higher plants, photosystem II （PSII） is a large pigment-protein supramolecular complex composed of the PSII core complex and the plant-specific peripheral light-harvesting complexes （LHCil）. PSli-LHCII complexes are highly dynamic in their quantity and macro-organization to various environmental conditions. In this study, we reported a critical factor, the Arabidopsis Thylakoid Formation 1 （THF1） protein, which controls PSII-LHCII dynamics during dark- induced senescence and light acclimation. Loss-of-function mutations in THF1 lead to a stay-green phenotype in path- ogen-infected and senescent leaves. Both LHCII and PSll core subunits are retained in dark-induced senescent leaves of thfl, indicative of the presence of PSII-LHCII complexes. Blue native （BN）-polyacrylamide gel electrophoresis （PAGE） and immunoblot analysis showed that, in dark- and high-light-treated thfl leaves, a type of PSII-LHCII megacomplex is selec- tively retained while the stability of PSII-LHCII supercomplexes significantly decreased, suggesting a dual role of THF1 in dynamics of PSII-LHCII complexes. We showed further that THF1 interacts with Lhcb proteins in a pH-dependent manner and that the stay-green phenotype of thfl relies on the presence of LHCII complexes. Taken together, the data suggest that THF1 is required for dynamics of PSII-LHCII supramolecular organization in higher plants.     

Influence of Nitrogen Fertilizer and Endophyte Infection on Ecophysiological Parameters and Mineral Element Content of Perennial Ryegrass

An experiment was designed to determine the effect of the fungal endophyte Neotyphodium Iolii on the growth, physiological parameters and mineral element content of perennial ryegrass （Lolium perennel L.）, when growing at two N supply levels. Endophyte infection had a significant positive effect on both shoot and root growth of ryegrass, but this difference was only significant in the high N supply treatment. At high N supply, endophyte-infected （El） plants accumulated more soluble sugar in the sheath and the root than endophyte-free （EF） plants. Endophyte infection affected mineral element concentrations in the root more than in the shoot. We found a significant effect of endophyte infection on B, Mn and Mg in the root, but significant effect was only found on B in the shoot. El plants tended to accumulate less B in the shoot at both N levels, but accumulated more B, Mn and Mg in the root at low N levels. The difference of growth parameters in different periods was significant. The content of soluble sugar and crude protein in the sheath were also dependent on the growth stages of both El and EF plants.     

Growth and Contaminant Removal Effect of Several Plants in Constructed Wetlands

The aim of the present study is to probe the relation between plant growth and its decontamination effect in constructed wetlands. Four species were studied in the small-scale mono-cultured constructed wetlands, which were fed with domestic wastewater. Plant growth indexes were correlated with contaminant removal performance of the constructed wetlands. Wetlands planted with Cyperus flabelliformis Rottb. showed the highest growth indexes such as shoot growth, biomass, root activity, root biomass increment, and the highest contaminant removal rates, whereas wetlands planted with Vetiveria zizanioides L. Nash had the lowest growth indexes and the lowest removal rates. Above-ground biomass and total biomass were significantly correlated with ammonia nitrogen removal, and below-ground biomass with soluble reactive phosphorus removal. Photosynthetic rate had higher correlation with nitrogen removal in these species. Root activity and root biomass increment was more correlated with 5 d biochemical oxygen demand removal. Chemical oxygen demand removal had lower correlations with plant growth indexes. All four species had higher removal rates in summer and autumn. The results suggest that the effect of plant growth on contaminant removal in constructed wetlands were different specifically in plants and contaminants.     

Arabidopsis Coordinates the Diurnal Regulation of Carbon Allocation and Growth across a Wide Range of Photoperiods

In short photoperiods, plants accumulate starch more rapidly in the light and degrade it more slowly at night, ensuring that their starch reserves last until dawn. To investigate the accompanying changes in the timing of growth, Arabidopsis was grown in a range of photoperiods and analyzed for rosette biomass, photosynthesis, respiration, ribosome abundance, polysome loading, starch, and over 40 metabolites at dawn and dusk. The data set was used to model growth rates in the daytime and night, and to identify metabolites that correlate with growth. Modeled growth rates and polysome loading were high in the daytime and at night in long photoperiods, but decreased at night in short photoperiods. Ribosome abundance was similar in all photoperiods. It is discussed how the amount of starch accumulated in the light period, the length of the night, and maintenance costs interact to constrain growth at night in short photoperiods, and alter the strategy for optimizing ribosome use. Significant correlations were found in the day- time and the night between growth rates and the levels of the sugar-signal trehalose 6-phosphate and the amino acid biosynthesis intermediate shikimate, identifying these metabolites as hubs in a network that coordinates growth with diurnal changes in the carbon supply.     

Protein engineering,expression, and activity of a novel fusion protein possessing keratinocyte growth factor 2 and fibronectin

Growthh factor-induced proliferation and differentiation often require adhesion of cells to the extracellular matriv proteins such as fibronectin （FN）. in this study, we aimed to investigate the effect of protein engineering of the keratinocyte growth factor 2 （KGF2） fused to the FN on the mitogenic activity of KGF2. The fusion pratein （KGF2-FN10）, which was expressed in Escherichia coil, showed significantly enhanced mitogenie activity of KGF2 on human keratinocytes. Moreover, KGF2-FN10 fusion protein showed significantly increased activity to differentiate keratinocytes from native KGF2. In conclusion, these results suggest that KGF2-FN10 fusion protein has certain advantages over native KGF2 and may offer a novel strategy to potentiate the therapeutic effect of KGF2.     

Effect of Incubation Temperature on the Somatic Development of the Snail-Eating Turtle Malayemys macrocephala

The rising average global temperature can lead to changes both in the physical and biological environments and affect the survival of organisms. Freshwater turtles are considered to be susceptible species since their development is dependent on incubation temperature. In Thailand, although several species of freshwater turtle are present, the extent of their susceptibility to temperature change is unknown due to the lack of information on their developmental patterns. This research, therefore, is aimed at examining the effects of temperature on somatic development in Malayemys macrocephala, a native species and the most common freshwater turtle in Thailand. Turtle eggs were collected from rice fields in the central part of Thailand during December 2011 to February 2012 inclusive. Eggs （237-238 per condition） were incubated in microprocessor-controlled incubators at three different temperatures （26 ℃, 29℃ and 32℃） with a relative humidity in excess of 80%. Each week, until the remaining eggs hatched, eggs were randomly selected, removed and dissected to reveal the developing embryo to screen for developmental stage and any abnormalities. The incubation period （lay to hatch） was not significantly different among the three temperatures （115 ±11.3 d, 115 ±20.3 d and 109±17.8 d, respectively）, but the growth patterns, as indicated by the stages of development and carapace lengths, were significantly different. At a high temperature （32℃）, turtle embryos showed a significantly faster growth rate than at the intermediate and low temperatures （29 ℃and 26 ℃）, but had a significantly （over 3.3-fold） higher incidence of developmental abnormalities （especially deformed bodies） than at the lower temperatures. Overall, the results indicate that incubation temperature is an important variable affecting the somatic development of this tropical freshwater turtle species, whilst abnormalities in the embryonic body may be a sensitive indicator of extreme thermal stress.     

Interaction between a Dark Septate Endophytic Isolate from Dendrobium sp. and Roots of D. nobile Seedlings

Interactions between an isolate of dark septate endophytes （DSE） and roots of Dendrobium nobile Lindl. seedlings are reported in this paper. The isolate was obtained from orchid mycorrhizas on Dendrobium sp. in subtropical forest. The fungus formed typical orchid mycorrhiza in aseptic co-culture with D. nobile seedlings on modified Murashige-Skoog （MMS） medium. Anatomic observations of the infected roots showed that the DSE hyphae invaded the velamen layer, passed through passage cells in exodermis, entered the cortex cells, and then formed fungal pelotons of orchid mycorrhiza. D. nobile seedlings＇ plant height, stem diameter, new roots number and biomass were greatly enhanced by inoculating the fungus to seedlings. The fungus was identified as Leptodontidium by sequencing the polymerase chain reaction-amplified rDNA ITS1-5,8S-ITS2 （internal transcribed spacer （ITS）） regions and comparison with similar taxa.     

Protein engineering of a fibroblast growth factor-1 fusion protein with cell adhesive activity

Fibroblast growth factor-1 （FGF1） is one of the most potent angiogenic growth factors, and also plays an important role in regulating cellular functions including cell proliferation, motility, differentiation, survival, and tissue regeneration processes. Here we described a novel fusion protein that was designed by combining the cell adhesion sequence from fibronectin with FGF1. The F1-Fn fusion protein functions as a minimized protein that directs integrin-dependent cell adhesion and stimulates cellular responses including cell proliferation and differentiation. Moreover, our results indicate that Fn-mediated signaling synergizes with signals from FGF1 in promoting cellular adhesion, proliferation, and differentiation in MG63 cells.     

Arabinan Metabolism during Seed Development and Germination in Arabidopsis

Arabinans are found in the pectic network of many cell walls, where, along with galactan, they are present as side chains of Rhamnogalacturonan I. Whilst arabinans have been reported to be abundant polymers in the cell walls of seeds from a range of plant species, their proposed role as a storage reserve has not been thoroughly investigated. In the cell walls of Arabidopsis seeds, arabinose accounts for approximately 40% of the monosaccharide composition of non- cellulosic polysaccharides of embryos. Arabinose levels decline to -15% during seedling establishment, indicating that cell wall arabinans may be mobilized during germination. Immunolocalization of arabinan in embryos, seeds, and seedlings reveals that arabinans accumulate in developing and mature embryos, but disappear during germination and seedling establishment. Experiments using 14C-arabinose show that it is readily incorporated and metabolized in growing seedlings, indicating an active catabolic pathway for this sugar. We found that depleting arabinans in seeds using a fungal arabinanase causes delayed seedling growth, lending support to the hypothesis that these polymers may help fuel early seedling growth.     

Oxygation Enhances Growth,Gas Exchange and Salt Tolerance of Vegetable Soybean and Cotton in a Saline Vertisol

Impacts of salinity become severe when the soil is deficient in oxygen. OxygaUon （using aerated water for subsurface drip irrigation of crop） could minimize the impact of salinity on plants under oxygen-limiting soil environments. Pot experiments were conducted to evaluate the effects of oxygation （12% air volume/volume of water） on vegetable soybean （moderately salt tolerant） and cotton （salt tolerant） in a salinized vertisol at 2, 8, 14, 20 dS/m ECe. In vegetable soybean, oxygation increased above ground biomass yield and water use efficiency （WUE） by 13% and 22%, respectively, compared with the control. Higher yield with oxygation was accompanied by greater plant height and stem diameter and reduced specific leaf area and leaf Na^＋ and CI^- concentrations. In cotton, oxygation increased lint yield and WUE by 18% and 16%, respectively, compared with the control, and was accompanied by greater canopy light interception, plant height and stem diameter. Oxygation also led to a greater rate of photosynthesis, higher relative water content in the leaf, reduced crop water stress index and lower leaf water potential. It did not, however, affect leaf Na^＋ or CI^- concentration. Oxygation invariably increased, whereas salinity reduced the K^＋： Na^＋ ratio in the leaves of both species. Oxygation improved yield and WUE performance of salt tolerant and moderately tolerant crops under saline soil environments, and this may have a significant impact for irrigated agriculture where saline soils pose constraints to crop production.     

Growth-Defense Tradeoffs in Plants： A Balancing Act to Optimize Fitness

Growth-defense tradeoffs are thought to occur in plants due to resource restrictions, which demand prior- itization towards either growth or defense, depending on external and internal factors. These tradeoffs have profound implications in agriculture and natural ecosystems, as both processes are vital for plant survival, reproduction, and, ulti- mately, plant fitness. While many of the molecular mechanisms underlying growth and defense tradeoffs remain to be elucidated, hormone crosstalk has emerged as a major player in regulating tradeoffs needed to achieve a balance. In this review, we cover recent advances in understanding growth-defense tradeoffs in plants as well as what is known regard- ing the underlying molecular mechanisms. Specifically, we address evidence supporting the growth-defense tradeoff concept, as well as known interactions between defense signaling and growth signaling. Understanding the molecular basis of these tradeoffs in plants should provide a foundation for the development of breeding strategies that optimize the growth-defense balance to maximize crop yield to meet rising global food and biofuel demands.     

Molecular Characterization of the Calvin Cycle Enzyme Phosphoribulokinase in the Stramenopile Alga Vaucheria litorea and the Plastid Hosting Mollusc Elysia chlorotica

Phosphoribulokinase （PRK）, a nuclear-encoded plastid-localized enzyme unique to the photosynthetic carbon reduction （Calvin） cycle, was cloned and characterized from the stramenopile alga Vaucheria litorea. This alga is the source of plastids for the mollusc （sea slug） Elysia chlorotica which enable the animal to survive for months solely by photoautotrophic CO2 fixation. The 1633-bp V. litorea prk gene was cloned and the coding region, found to be interrupted by four introns, encodes a 405-amino acid protein. This protein contains the typical bipartite target sequence expected of nuclearencoded proteins that are directed to complex （i.e. four membrane-bound） algal plastids. De novo synthesis of PRK and enzyme activity were detected in E. chlorotica in spite of having been starved of V. litorea for several months. Unlike the algal enzyme, PRK in the sea slug did not exhibit redox regulation. Two copies of partial PRK-encoding genes were isolated from both sea slug and aposymbiotic sea slug egg DNA using PCR. Each copy contains the nucleotide region spanning exon 1 and part of exon 2 of V litorea prk, including the bipartite targeting peptide. However, the larger prk fragment also includes intron 1. The exon and intron sequences of prk in E. chlorotica and V/itorea are nearly identical. These data suggest that PRK is differentially regulated in V. litorea and E. chlorotica and at least a portion of the V. litorea nuclear PRK gene is present in sea slugs that have been starved for several months.     

Identification,expression, and characterization of the highly conserved D-xylose isomerase in animals

D-xylose is a necessary sugar for animals. The xylanase from a mollusk, Ampullaria crossean, was previously reported by our laboratory. This xylanase can degrade the xylan into D-xylose. But there is still a gap in our knowledge on its metabolic pathway. The question is how does the xylose enter the pentose pathway？ With the help of genomic databases and bioinformatic tools, we found that some animals, such as bacteria, have a highly conserved D-xylose isomerase （EC 5.3.1.5）. The xyiose isomerase from a sea squirt, Ciona intestinali, was heterogeneously expressed in Escherichia coli and purified to confirm its function. The recombinant enzyme had good thermal stability in the presence of Mg^2＋. At the optimum temperature and optimum pH environment, its specific activity on D-xylose was 0.331 μmol/mg/min. This enzyme exists broadly in many animals, but it disappeared in the genome of Amphibia-like Xenopus laevis. Its sequence was highly conserved. The xylose isomerases from animals are very interesting proteins for the study of evolution.     

Chloroplast Proteomics and the Compartmentation of Plastidial Isoprenoid Biosynthetic Pathways

Recent advances in the proteomic field have allowed high-throughput experiments to be conducted on chloroplast samples. Many proteomic investigations have focused on either whole chloroplast or sub-plastidial fractions. To date, the Plant Protein Database （PPDB, Sun et al., 2009） presents the most exhaustive chloroplast proteome available online. However, the accurate localization of many proteins that were identified in different sub-plastidial compartments remains hypothetical. Ferro et al. （2009） went a step further into the knowledge of Arabidopsis thaliana chloroplast proteins with regards to their accurate localization within the chloroplast by using a semi-quantitative proteomic approach known as spectral counting. Their proteomic strategy was based on the accurate mass and time tags （AMT） database approach and they built up AT_CHLORO, a comprehensive chloroplast proteome database with sub-plastidial localization and curated information on envelope proteins. Comparing these two extensive databases, we focus here on about 100 enzymes involved in the synthesis of chloroplast-specific isoprenoids. Well known pathways （i.e. compartmentation of the methyl erythritol phosphate biosynthetic pathway, of tetrapyrroles and chlorophyll biosynthesis and breakdown within chloroplasts） validate the spectral counting-based strategy. The same strategy was then used to identify the precise localization of the biosynthesis of carotenoids and prenylquinones within chloroplasts （i.e. in envelope membranes, stroma, and/or thylakoids） that remains unclear until now.     

The Translational Apparatus of Plastids and Its Role in Plant Development

Chloroplasts （plastids） possess a genome and their own machinery to express it. Translation in plastids occurs on bacterial-type 70S ribosomes utilizing a set of tRNAs that is entirely encoded in the plastid genome. In recent years, the components of the chloroplast translational apparatus have been intensely studied by proteomic approaches and by reverse genetics in the model systems tobacco （plastid-encoded components） and Arabidopsis （nucleus-encoded components）. This work has provided important new insights into the structure, function, and biogenesis of chloroplast ribosomes, and also has shed fresh light on the molecular mechanisms of the translation process in plastids. In addition, mutants affected in plastid translation have yielded strong genetic evidence for chloroplast genes and gene products influencing plant develop- ment at various levels, presumably via retrograde signaling pathway（s）. In this review, we describe recent progress with the functional analysis of components of the chloroplast translational machinery and discuss the currently available evidence that supports a significant impact of plastid translational activity on plant anatomy and morphology.     

The Response Difference of Mitochondria in Recalcitrant Antiaris toxicaria Axes and Orthodox Zea mays Embryos to Dehydration Injury

Long-term preservation of recalcitrant seeds is very difficult because the physiological basis on their desiccation sensitivity is poorly understood. Survival of Antiaris toxicaria axes rapidly decreased and that of immature maize embryos very slowly decreased with dehydration. To understand their different responses to dehydration, we examined the changes in mitochondria activity during dehydration. Although activities of cytochrome （Cyt） c oxidase and malate dehydrogenase of the A. toxicaria axis and maize embryo mitochondria decreased with dehydration, the parameters of maize embryo mitochondria were much higher than those of A. toxicaria, showing that the damage was more severe for the A. toxicaria axis mitochondria than for those of maize embryo. The state I and III respiration of the A. toxicaria axis mitochondria were higher than those of maize embryo, the former rapidly decreased, and the latter slowly decreased with dehydration. The proportion of Cyt c pathway to state III respiration for the A. toxicaria axis mitochondria was low and rapidly decreased with dehydration, and the proportion of alternative oxidase pathway was high and slightly increased with dehydration. In contrast, the proportion of Cyt c pathway for maize embryo mitochondria was high, and that of alternative oxidase pathway was low. Both pathways decreased slowly with dehydration.     

Response of Chinese Wampee Axes and Maize Embryos to Dehydration at Different Rates

Survival of wampee （Clausena lansium Skeels） axes and maize （Zea mays L.） embryos decreased with rapid and slow dehydration. Damage of wampee axes by rapid dehydration was much less than by slow dehydration, and that was contrary to maize embryos. The malondialdehyde contents of wampee axes and maize embryos rapidly increased with dehydration, those of wampee axes were lower during rapid dehydration than during slow dehydration, and those of maize embryos were higher during rapid dehydration than during slow dehydration. Activities of superoxide dismutase （SOD）, ascorbate peroxidase （APX） and catalase （CAT） of wampee axes markedly increased during the early phase of dehydration, and then rapidly decreased, and those of rapidly dehydrated axes were higher than those of slow dehydrated axes when they were dehydrated to low water contents. Activities of SOD and APX of maize embryos notable decreased with dehydration. There were higher SOD activities and lower APX activities of slowly dehydrated maize embryos compared with rapidly dehydrated maize embryos. CAT activities of maize embryos markedly increased during the early phase of dehydration, and then decreased, and those of slowly dehydrated embryos were higher than those of rapidly dehydrated embryos during the late phase of dehydration.     

Cortactin is involved in transforming growth factor-β1-induced epithelial-mesenchymal transition in AML-12 cells

Cortactin is an F-actin binding protein, regulating cell movement and adhesive junction assembly. However, the function of cortactin in epithelial-mesenchymal transition （EMT） remains elusive. Here we found that during transforming growth factor-β1 （TGF-β1）- induced EMT in AML-12 murine hepatocytes, cortactin underwent tyrosine dephosphorylation. Inhibition of the dephosphorylation of eortactin by sodium vanadate blocked TGF-β1-induced EMT. Knockdown of cortactin by RNAi led to decrease of intercellular junction proteins E-cadherin and Zonula occludens-1 and induced expression of mesenchymal protein fibronectin. Additionally, knockdown of cortactin further promoted TGF-β1-induced EMT in AML-12 cells, as determined by EMT markers and cell morphological changes. Moreover, migration assay showed that cortactin knockdown promoted the migration of AML-12 cells, and also enhanced TGF-β1-induced migration. Our study showed the involvement of cortactin in the TGF- β1-induced EMT.