Natural gums exude from trees and shrubs in tear-like, then dried in the sun, forming hard and glassy exudates of different colors. They are consisted of mainly polysaccharides, and used in the food, pharmaceutical and chemical industries for emulsification, thickening, stabilization and other processes. Gummosis, the process of the induction, accumulation and exudation of gums, is found throughout the plant kingdom. Gummosis has been also known as a common defense response to various biotic and abiotic environmental stresses such as bacterial and fungal infections, insect damages and mechanical injuries, since gums can impede the spread of diseases by isolating and sealing infected or infested tissues, thus, preventing entry and movement of pathogens, the loss of water from the damaged tissues and other harmful occurrences. The author has studied hormonal regulation of gummosis and sugar composition of gum polysaccharides in trees and fruits in stone-fruit species of the family Rosaceae, and in bulbs and shoots of several bulbous plants, resulting in the conclusion that sugar metabolism producing gums is regulated by signal network of jasmonates and ethylene, whereas sugar metabolisms and key hormone relevance to gummosis are different among plant species. Chemical composition of gums in different plant species is also described.

Terpenoids are one of the largest classes of natural products in all organisms. The numerous chemical structures and biological functions in terpenoids are brought by variety of carbon skeletons and chemical modification. In terpenoid biosynthesis, terpene cyclases are key enzymes to build a multitude of carbon skeletons. We analyzed function of diterpene cyclases involved in diterpenoid plant hormone gibberellin and the related derivatives from fungi and bryophytes. ent-Kaurene synthases in both fungi and bryophytes are bifunctional diterpene cyclases (CPS/KS) catalyzing two-step cyclization reaction from geranylgeranyl diphosphate (GGDP) to ent-kaurene via ent-copalyl diphosphate (ent-CDP), whereas two monofunctional diterpene cyclases (ent-CDP synthase and ent-kaurene synthase) are involved in ent-kaurene biosynthesis in vascular plants including lycophytes. Structure and enzyme function of CPS/KS in Physcomitrella patens proposed a quenching mechanism of ent-kauranyl cation during the cyclization reaction. The moss P. patens has no ent-kaurenoic acid oxidase (CYP88A) genes that encode cytochrome P450 monooxidase catalyzing the oxidation reaction from ent-kaurenoic acid to GA_<12>. Although the ent-kaurene-deficient mutant of P. patens showed abnormal growth of protonemata under the blue-light, the growth was recovered by application of ent-kaurenoic acid. Thus, novel ent-kaurene-derived diterpenoids may regulate a unique photomorphogenesis of P. patens under the blue light.

Studies have indicated that most of plant hormones are mobile. However, it was unclear how the transport of hormones is regulated. In this study, we developed a system to functionally identify plant hormone transporters. A yeast two-hybrid system with the abscisic acid (ABA) receptor and PP2C protein phosphatase was used to detect ABA transport activities of proteins expressed in yeast cells. We found that a member of Arabidopsis NRT1/PTR FAMILY (NPF) proteins, NPF4.6, could induce interactions between the ABA receptor and PP2C under low ABA concentrations. ABA transport activities of NPF4.6 was confirmed by directly analyzing the compound taken into yeast or insect cells by LC-MS/MS. Finally, characterization of mutants defective in NPF4.6 demonstrated that the protein functions as an ABA transporter in vivo. Interestingly, we found that NPF proteins transported not only ABA, but also gibberellin and jasmonoyl-isoleucine, suggesting that they might function as transporters of these hormones.

Plants biosynthesize an excess of bioactive phytochemicals (primary metabolites and specialized metabolites) that have primary functions in photosynthesis, respiration, growth and development and specialized functions in ecological interactions and defense against plant pathogens and herbivores.Cytochrome P450 monooxygenases (P450s) play crucial roles in terpenoids biosynthesis and metabolism. 1)BR campestanol-independent pathway Recent molecular genetic studies for BR-deficient mutants of Arabidopsis, rice, tomato and garden pea have identified several P450 genes (CYP85A, 90A, 90B, 90C, 90D, 724B) so far.We, here, present that functional characterization of P450 enzymes involved in brassinosteroids biosynthesis led to the elucidation of the novel BR short-cut route (named campestanol-independent pathway). 2)CYP720 family in conifer chemical defense Recent gene discovery and phylogenetic cluster analysis for conifer P450s revealed that the CYP720 subfamily consists of over 30 P450s. Here, we report new results from the biochemical characterization of CYP720B4.In vitro assay results show that this P450 catalyze three oxidation steps at the C-18 position of abietine to form abietic acid, and also oxidize other diterpenoid olefins to the corresponding resin acids.

The cell wall is a characteristic component of plant cells, whose structure and composition vary depending on the cell type, developmental stage, and environmental condition. For construction and proper modulation of the cell wall, a vast number of proteins and polysaccharides should be transported to the plasma membrane and/or the extracellular space correctly. The delivery of these materials depends on the membrane trafficking system, a key mechanism of intracellular transport connecting single-membrane bounded organelles and the extracellular space. Although molecular mechanisms of membrane trafficking are largely conserved in eukaryotic lineages, plants could have developed unique trafficking mechanisms to construct the cell wall and maintain its integrity, given the plant-specific nature of the cell wall. In this review, we summarize recent progress in the field of membrane trafficking in plant cells, especially focusing on the cell wall.

The plant cytoskeleton, which consists of microtubules and actin microfilaments, shows dynamic structural changes during the progression of the cell cycle. The cytoskeleton plays significant roles in cell shape and cell movement, and especially in cell division, including nuclear division and cytokinesis. In animal cells, the actin contractile ring divides cells centripetally. In contrast, flowering plants have a rigid cell wall around their cells, and therefore, the cells must divide in a physically restricted space. To accomplish cell division, components of the cytoskeletal mitotic apparatus appear in the following order : the preprophase band (PPBs) from the late G_2 phase to prophase, the mitotic spindle from prometaphase to anaphase, and the phragmoplast at telophase. The phragmoplast is a structure specific to plant cells that develops centrifugally on an equatorial plane.It forms the "cell plate" by serving as a scaffold for its assembly during successive stages of cytokinesis. The cell plate subsequently develops into a new cell wall that separates the two daughter cells. In this article, we summarize our research on the structure of the plant cytoskeleton and its roles in cell plate formation.

Lignification is an important differentiation process in plant cell walls in which lignin is deposited in the polysaccharide matrix. The actual chemical structure of the lignin polymer is still unclear for several reasons : it has multiple structural units and bonding patterns ; it is entangled with the polysaccharide matrix and, therefore, very difficult to isolate ; and the lignin structure may vary among the different cells and tissues in plants. The controlling mechanism of lignin formation is also still controversial. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been used to investigate the structure and formation of lignin in individual cells ; herein, those lignin studies are reviewed. TOF-SIMS is a rapidly developing analytical method that can provide mass spectral information with submicron lateral resolution. The main polymer components of plant cell walls (cellulose, hemicellulose, and lignin) are detected as fragment ions in the TOF-SIMS spectra. Because an understanding of fragmentation behavior is essential in order to discuss the original structure, such behavior is described in detail. Subsequently, practical results on the relative amounts and the structure of the lignin in specific tissues are introduced. The latest advances in cryo-TOF-SIMS, which allows the analysis of frozen-hydrated samples, are also described. Cryo-TOF-SIMS is a powerful visualization tool, especially for water-soluble compounds of nearly equal distributions in a living system. The heterogeneous distribution of the many chemical components in plants should provide useful information for innovative discussions of the various mechanisms in plants.

Minerals play important roles in plant cell wall. Among the components of cell walls, pectin is most important in terms of interaction with minerals. Calcium(Ca) and boron(B) are essential elements for plants. Ca and B binding to homogalacturonan (HG) and rhamnogalacturonan-II (RG-II) domains of pectin, respectively, affects physical and chemical properties of the cell wall through formation of pectic network in primary cell walls, thereby regulating cell growth and differentiation. For Ca and B to exert their functions in the cell wall, they have to be transported from soil through roots and properly localized within tissues. The present article reviews recent advances in molecular mechanisms underlying the pectin synthesis and Ca and B transport for cell wall binding, which is required for normal growth and development in plants. Possible function of pectin as a signal molecule and feedback regulation for cell wall integrity are also discussed.

The apoplast is the space outside the plasma membrane, consisting of the cell wall and its outer space. The apoplastic solution contains a wide variety of small molecules, some of which are taken up from soil with water. In addition, some chemicals biosynthesized in the cell are secreted into the apoplastic region through the plasma membrane. Xylem sap contains many of these small chemicals including signaling molecules, thus the apoplastic region has an important role in the translocation of these small signaling molecules. In this review, we describe recent topics on the movement and functions of selected hormonal molecules that are transported over a long distance through the xylem. In a broad sense, the long distance translocation of signaling molecules through the apoplast can be considered as a part of "the information processing system of the plant cell wall".

Plants evolved a multilayered immune system against pathogenic microbes and insect herbivores. Plant cell wall and apoplast consist an essential component of this immune system as the first line of defense, where plant cells contact with these invaders. Plant immune responses can be triggered by the recognition of conserved microbial signature called MAMP (Microbe-associated molecular pattern) at the apoplastic region. In the plant immune system, plant cell wall can function as a barrier against invasion and also a sensor for pathogen attack. Alteration of cell wall integrity and the generation of cell wall-derived fragments are both considered to induce plant immune responses. These MAMPs and damage signals (including DAMPs, Damage-associated molecular patterns) trigger the generation of anti-microbial compounds in the apoplastic region and the reinforcement of the cell wall. On the other hand, pathogenic microbes evolved effector systems to inhibit/escape from the host defense machinery and surveillance system. These battles at the molecular level between plants and microbes often take place in the apoplast. It has also been becoming clear that the plant cell walls are involved in the detection of and defense responses against insect herbivores. Thus plant cell wall and apoplast are not only important as the battle field where host plants and invading organisms compete for the detection and defense responses but also important as a sensor and barrier for these invaders.

The liverwort, Marchantia polymorpha L., is an emerging model plant. During the past several years, various molecular biological techniques for M. polymorpha have been developed. Recently, we reported an easy Agrobacterium-mediated genetic transformation method, for M. polymorpha, which is termed AgarTrap (Agar-utilized Transformation with Pouring Solutions). AgarTrap method could be carried out only by exchanging appropriate solutions in a single Petri dish within a week, and it could produce a sufficient number of independent transformants. Because AgarTrap is rapid and easy technology, this method will promote molecular biological study of M. polymorpha.

The root-parasitic weed Striga hermonthica is a major biotic constraint to cereal production in sub-Saharan Africa. Striga seeds germinate only when exposed to host root-derived stimulants, strigolactones (SLs). Induction of Striga germination in the absence of host plants, suicidal germination, is an attractive approach to control the parasite. However, limited studies are available on demonstration of the approach using synthetic SL analogues under field conditions. Using an active synthetic analogue, a carbamate designated as T-010, which was easy in preparation, the practicality of suicidal germination in combating Striga was demonstrated under field conditions.