Photosynthetic capacity of leaves varies greatly among C₃ species although they have the same photosynthetic metabolisms. Here we discuss mechanisms underlying interspecific variation in photosynthetic capacity. Within-species variation in photosynthetic capacity is generally explained by nitrogen concentration because photosynthetic nitrogen-use efficiency (PNUE, photosynthetic capacity per unit leaf nitrogen) tends to be constant in each species. Among-species variation, on the other hand, involves both variations in nitrogen concentration and PNUE. Species with higher photosynthetic capacity have higher nitrogen concentration per mass and PNUE. Interspecific variation in PNUE is attributable to CO₂ diffusion in the leaves, nitrogen allocation to the photosynthetic apparatus and/or specific activity of photosynthetic enzymes. Previous studies have shown that variations in mesophyll conductance and nitrogen allocation explain the variation in PNUE. As new leaves are constructed by assimilated nitrogen and carbon, increased carbon assimilation rates are expected to dilute nitrogen in the leaves. However, this expectation contradicts the fact that photosynthetic capacity and nitrogen concentration is positively related with each other across species. This paradoxical dilution effect may be compensated by root activity, i.e. species with higher photosynthetic capacity have higher root activity to maintain higher leaf nitrogen concentrations.

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Nucleotide sugars are activated forms of monosaccharides and serve as glycosyl donors for glycosyltransferases in the synthesis of cell wall polysaccharides. Since they affect the amounts and architecture of cell wall polysaccharides in plants, the levels of nucleotide sugars, as well as the levels of the glycosyltransferases, at least partially, regulate the production of plant cellulosic biomass. Nucleotide sugars are principally generated through de novo pathways, in which various UDP- and GDP-sugars are produced through sequential interconversions from starting substrates such as UDP-glucose. The salvage pathway is an alternative route to synthesize nucleotide sugars. In the salvage pathway, free monosaccharides released during the metabolism of polysaccharides and glycoconjugates are first phosphorylated by monosaccharide kinases, and then converted to nucleotide sugars by nucleotide sugar pyrophosphorylases in the presence of the respective nucleotide triphosphates as co-substrates. In this review, we focus on the recent progress in our understanding of the mechanism for the generation of nucleotide sugars through the salvage pathway for free monosaccharides in higher plants.

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Woody cells develop secondary wall structure that mainly consists of polysaccharides (cellulose and hemicellulose) and lignin. These components are expected to be new sources of biofuels and biomaterials. Therefore, it is important to understand the molecular mechanism underlying secondary wall formation and how it contributes to plant biomass. Plant-specific NAC domain transcription factor family has been shown to be involved in diverse biological functions. Recently, several studies reported that a subfamily of the NAC domain transcription factors plays pivotal roles in secondary wall formation. In this review, we have summarized the role of NAC domain transcription factors in controlling the secondary wall formation.

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Liquid crystalline (LC) polymers were prepared by an in-bulk polycondensation of bioavaliable aromatic hydroxyl(carboxylic acid)s. p-Coumaric acid (4HCA) and its derivatives were selected as phytomonomers. The 4HCA homopolymer showed a thermotropic LC phase only in a state of low molecular weight. The copolymers of 4HCA with bile acids such as lithocholic acid (LCA) and cholic acid (CA) showed excellent cell compatibilities but low molecular weights. However, P(4HCA-co-CA)s allowed LC spinning to create molecularly oriented biofibers, presumably due to the chain entanglement that occurs during in-bulk chain propagation into hyperbranching architecture. P{4HCA-co-3,4-dihydroxycinnamic acid (DHCA)}s showed high molecular weight, high mechanical strength, high Young's modulus, and high softening temperature, which may be achieved through the entanglement by in-bulk formation of hyperbranching, rigid structures. P(4HCA-co-DHCA)s showed a smooth hydrolysis, in-soil degradation, and photo-tunable hydrolysis. Thus, P(4HCA-co-DHCA)s might be applied as an environmentally degradable plastic with extremely high performance.

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Heterologous expression of plant genes, particularly those encoding carbohydrate-active enzymes such as glycoside hydrolases and glycosyl transferases, continues to be a major hurdle in the functional analysis of plant proteomes. Presently, there are few convenient systems for the production of recombinant plant enzymes in active form and at adequate levels for biochemical and structural characterization. The methylotrophic yeast Pichia pastoris is an attractive expression host due to its ease of manipulation and its capacity to perform post-translational protein modifications, such as N-glycosylation [Daly and Hearn (2005) J Mol Recognit 18: 119–138]. Here, we demonstrate the utility of the P. pastoris SMD1168H/pPICZ-alpha C system for the expression of a range of xyloglucan endo-transglycosylase/hydrolase (XTH) cDNAs from barley (Hordeum vulgare). Although stable transformants were readily obtained by positive selection for vector-induced antibiotic resistance for all of the nine constructs tested, only five isoforms were secreted as soluble proteins into the culture medium, four in active form. Furthermore, production levels of these five isoforms were found to be variable, depending on the transformant, which further underscores the necessity of screening multiple clones for expression of active enzyme. Failure to express certain XTH isoforms in P. pastoris could not be correlated with any conserved gene or protein sequence properties, and this precluded using rational sequence engineering to enhance heterologous expression of the cDNAs. Thus, while significant advances are reported here, systems for the heterologous production of plant proteins require further development.

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A gene encoding a family 51 α-L-arabinofuranosidase (At3g10740) is specifically expressed at the stage of xylem vessel formation in Arabidopsis thaliana. To investigate the role of the enzyme in the xylem vessel formation, the recombinant protein was expressed in Pichia pastoris and the properties were characterized. The enzyme showed optimal activity at pH 4.5 and 50°C and was stable over the pH range of 4.0–7.0 under 30°C. The enzyme released L-arabinose from p-nitrophenyl-α-L-arabinofuranoside, synthetic arabinofuranobiosides, arabinoxylo-oligosaccharides and arabinose-containing polysaccharides. The enzyme hydrolyzed p-nitrophenyl-α-L-arabinofuranoside but did not hydrolyze any other p-nitrophenyl-glycosides, and the specific activity for p-nitrophenyl-α-L-arabinofuranoside was 1.2 units mg⁻¹. Among the synthetic regioisomers of arabinofuranobiosides, the enzyme hydrolyzed all linkages that can occur between two α-L-arabinofuranosyl residues in the following order: α-1,5-linkage>α-1,2-linkage>α-1,3-linkage. The enzyme hydrolyzed arabinan, gum arabic, corn hull arabinoxylan, and wheat arabinoxylan. The enzyme showed higher activity for oligosaccharides than for polysaccharides. Furthermore, the enzyme preferentially hydrolyzed arabinoxylo-oligosaccharides such as O-α-L-arabinofuranosyl-1,3-O-β-D-xylopyranosyl-1,4-D-xylopyranoside and O-β-D-xylopyranosyl-1,4-[O-α-L-arabinofuranosyl-1,3]-O-β-D-xylopyranosyl-1,4-O-β-D-xylopyranoside, which were the hydrolysis products of xylan generated by a family 10 xylanase, in comparison to its activity for arabinofuranobiosides. These data suggest that the enzyme is involved in the modification of the structure of xylan together with family 10 xylanases during the xylem vessel formation.

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Xylem vessel elements play an important role in conducting water and nutrient in land plants. The in vitro culture system, in which subcultured Arabidopsis cells are induced to transdifferentiate into xylem vessel elements, was used to uncover the comprehensive gene expression profile by microarray analysis, which resulted in the identification of many genes encoding transcription factors including two transcriptional key regulators, VASCUAR-RELATED NAC DOMAIN6 (VND6) and VND7. Here we analyze the detailed expression pattern and function of ten genes encoding MYB transcription factors, MYB20, 43, 46, 52, 63, 83, 85, 99, 103, and 118, with the significantly up-regulated expression during the in vitro vessel element differentiation. Of these, six exhibited the specific expression in differentiating xylem vessels in Arabidopsis roots. In addition, MYB46 and MYB83 were shown to upregulate five of these MYB genes, MYB43, 52, 63, 85, and 103. Our results suggest that several MYB genes comprise a transcriptional network during xylem vessel element differentiation in roots.

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The basidiomycete Flammulina velutipes is one of the most popular edible mushrooms in Japan, and has the ability to grow on cellulosic biomass as a carbon source. In this study, we have isolated two enzymes belonging to glycoside hydrolase (GH) family 7 (FvCel7A and FvCel7B) from the cellulose-grown culture of the fungus, and cloned cDNAs encoding these enzymes by utilizing a transcriptomic database of this fungus. Although both enzymes contain a catalytic domain belonging to GH family 7, only FvCel7A has the family 1 carbohydrate-binding module at the C-terminal. Sequence comparison indicated that FvCel7A and FvCel7B have a similar pattern of disulfide bonds and similar active site architecture to other fungal GH family 7 enzymes, but show small differences at loop regions covering the active site, which may affect the reactivity of cellulosic substrates.

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Wood formation is a biological process of great economical importance. Genes active during the secondary cell wall formation of wood fibers from Populus tremula×tremuloides were previously identified by expression profiling through microarray analyses. A number of these genes encode glycosyltransferases (GTs) with unknown substrate specificities. Here we report heterologous expression of one of these enzymes, PttGT43A, a putative IRREGULAR XYLEM9 (IRX9) homologue. Expression trials in Pichia pastoris and insect cells revealed very low levels of accumulation of immunoreactive PttGT43A, whereas transient expression in Nicotiana benthamiana leaves by Agrobacterium infiltration (agroinfiltration) using a viral vector produced substantial amounts of protein that mostly precipitated in the crude pellet. Agroinfiltration induced weak endogenous xylosyltransferase activity in microsomal extracts, and transient PttGT43A expression further increased this activity, albeit only to low levels. PttGT43A may be inactive as an individual subunit, requiring complex formation with unknown partners to display enzymatic activity. Our results suggest that transient co-expression in leaves of candidate subunit GTs may provide a viable approach for formation of an active xylan xylosyltransferase enzymatic complex.

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The glycosyltransferases involved in plant cell wall biosynthesis are generally too low in concentration to allow for their purification. Therefore, the development of a method for enhanced solubilization of membrane proteins is necessary. Here, we report ribonuclease treatment of cell homogenates of azuki bean epicotyls. Polygalacturonic acid synthase, localized at the plant Golgi membrane, was enriched 2.0-fold in specific activity after ribonuclease treatment. Total enzyme activity per unit weight was also improved 2.1-fold. These data indicate that ribonuclease works to remove ribosomes from the microsomal fraction and enhances the solubilization of polygalacturonic acid synthase.

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Novel plant-derived, adhesive polymers have been investigated from natural sources as 3,4-dihydroxycinnamic acid (caffeic acid; DHCA) and 4-hydroxycinnamic acid (p-coumaric acid; 4HCA) modified by transesterification. These copolymers were found to show strong adhesive characteristics to metal surfaces, which were equivalent to conventional superglues from petroleum resources. This strong adhesive action was due to interactions between catechol groups present at the end of the polymer chains and the metal surfaces.

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