Sorption of 1-naphthol by plant cuticular fractions

The contribution of aliphatic-rich plant biopolymer to sorption of hydrophobic organic compounds is significantly important because of their preservation and accumulation in the soil environment, but sorption mechanism is still not fully understood. In this study, sorption of 1-naphthol by plant cuticular fractions was examined to better understand the contributions of respective fraction. Toward this end, cuticular materials were isolated from the fruits of tomato by chemical method. The tomato cuticle sheet consisted of waxes （6.5 wt%）, cuticular monomer （69.5 wt%）, and polysaccharide （24.0 wt%）. Isotherms of 1-naphthol to the cuticular fractions were nonlinear （N value （0.82 - 0.90）） at the whole tested concentration ranges. The K∞/Kow ratios for bulk cuticle （TC1）, dewaxed cuticle （TC2）, cutin （TC4）, and desugared cuticle （TC5） were larger than unity, suggested that tomato bulk cuticle and cutin are much powerful sorption medium. Sorption capability of cutin （TC4） was 2.4 times higher than the nonsaponifiable fraction （TC3）. The 1-naphthol interactions with tomato cuticular materials were governed by both hydrophobic-type interactions and polar （H-bonding） interactions. Removal of the wax and polysaccharide materials from the bulk tomato cuticle caused a significant increase in the sorption ability of the cuticular material. There was a linear negative trend between K∞ values and the amount of polysaccharides or fraction＇s polarities （（N＋O）/C）; while a linear positive relationship between K∞ values and the content ofcutin monomer （linear R^2 = 0.993） was observed for present in the cuticular fractions. Predominant sorbent of the hydrophobic organic compounds （HOCs） in the plant cuticular fraction was the cutin monomer, contributing to 91.7% of the total sorption of tomato bulk cuticle.

The Arabidopsis DSO/ABCG 11 Transporter Affects Cutin Metabolism in Reproductive Organs and Suberin in Roots

Apart from its significance in the protection against stress conditions, the cuticular cover is essential for proper development of the diverse surface structures formed on aerial plant organs. This layer mainly consists of a cutin matrix, embedded and overlaid with cuticular waxes, Following their biosynthesis in epidermal cells, cutin and waxes were suggested to be exported across the plasma membrane by ABCG-type transporters such as DSO/ABCG11 to the cell wall and further to extracellular matrix. Here, additional aspects of DSO/ABCG11 function were investigated, predomi- nantly in reproductive organs, which were not revealed in the previous reports. This was facilitated by the generation of a transgenic DSO/ABCG11 silenced line （dso-4） that displayed relatively subtle morphological and chemical phenotypes. These included altered petal and silique morphology, fusion of seeds, and changes in levels of cutin monomers in flowers and siliques. The dso-4 phenotypes corresponded to the strong DSO/ABCG11 gene expression in the embryo epidermis as well as in the endosperm tissues of the developing seeds. Moreover, the DSO/ABCG11 protein displayed polar localization in the embryo protoderm. Transcriptome analysis of the dso-4 mutant leaves and stems showed that reduced DSO/ABCG11 activity suppressed the expression of a large number of cuticle-associated genes, implying that export of cuticular lipids from the plasma membrane is a rate-limiting step in cuticle metabolism. Surprisingly, root suberin composition of dso-4 was altered, as well as root expression of two suberin biosynthetic genes. Taken together, this study provides new insights into cutin and suberin metabolism and their role in reproductive organs and roots development.

Signaling events during initiation of arbuscular mycorrhizal symbiosis

Under nutrient-limiting conditions, plants will enter into symbiosis with arbuscular mycorrhizal （AM） fungi for the enhancement of mineral nutrient acquisition from the surrounding soil. AM fungi live in close, intracellular association with plant roots where they transfer phosphate and nitrogen to the plant in exchange for carbon. They are obligate fungi, relying on their host as their only carbon source. Much has been discovered in the last decade concerning the signaling events during initiation of the AM symbiosis, including the identification of signaling molecules generated by both partners. This signaling occurs through symbiosis-specific gene products in the host plant, which are indispensable for normal AM development. At the same time, plants have adapted complex mechanisms for avoiding infection by pathogenic fungi, including an innate immune response to general microbial molecules, such as chitin present in fungal cell walls. How it is that AM fungal colonization is maintained without eliciting a defensive response from the host is still uncertain. In this review, we present a summary of the molecular signals and their elicited responses during initiation of the AM symbiosis, including plant immune responses and their suppression.

Characterization and Ectopic Expression of a Populus Hydroxyacid Hyd roxyci n nam oylt ra nsferase

Cutinized and suberized cell walls in plants constitute physiologically important environment interfaces. They act as barriers limiting the loss of water and nutrients and protecting against radiation and invasion of pathogens. The roles of cutin- and suberin polyesters are often attributed to their dominant aliphatic components, but the contri- bution of aromatic composition to their physiological function remains unclear. By functionally screening a subset of Populus trichocarpa BAHD/HXXXD acyltransferases, we identified a hydroxycinnamoyltransferase that shows specific transacylation activity on ~0-hydroxyacids using both feruloyl- and p-coumaroyl- CoA as the acyl donors. We named this enzyme P. trichocarpa hydroxyacid/fatty alcohol hydroxycinnamoyltransferase 1 （PtFHT1）. The ectopic expression of the PtFHT1 gene in Arabidopsis increased the incorporation of ferulate in root and seed suberins and in leaf cutin, but not that of p-coumarate, while the aliphatic load in both suberin and cutin polyesters essentially remained unaffected. The overaccumulation of ferulate in lipophilic polyester significantly increased the tolerance of transgenic plants to salt stress treatment; under sub-lethal conditions of salt stress, the ratios of their seed germination and seedling establishment were 50% higher than those of wild-type plants. Our study suggests that, although aromatics are the minor component of polyesters, they play important role in the sealing function of lipidic polymers in planta.

Sorption of chlorophenols onto fruit cuticles and potato periderm

To better understand the interaction mechanisms of plant surfaces with polar organic compounds, sorption of 4-chlorophenol, 2,4- dichlorophenol, and 2,4,6-trichlorophenol by fruit cuticles （i.e., tomato, apple, and pepper）, and potato tuber periderm were investigated. The roles of cuticular components （waxes, cutin, cutan and sugar） on sorption of chlorophenols are quantitatively compared. Cutin and waxes govern the sorption capacity of bulk apple cuticle by hydrophobic interactions. Potato periderm with highest sugar content exhibits the lowest sorption capability for the chlorophenols. With the increase of hydrophobicity （i.e., Kow ） of sorbate, the relative contribution of lipophilic components （wax, cutin and cutan） on total sorption increases, however, the ratios of Koc to Kow decreases due to increasing ionization degree of sorbates.

CUTIN SYNTHASE 2 Maintains Progressively Developing Cuticular Ridges in Arabidopsis Sepals

The cuticle is a crucial barrier on the aerial surfaces of land plants, in many plants, including Arabidopsis, the sepals and petals form distinctive nanoridges in their cuticles. However, little is known about how the formation and maintenance of these nanostructures is coordinated with the growth and development of the underlying cells. Here we report the characterization of the Arabidopsis cutin synthase 2 （cus2） mutant, which causes a great reduction in cuticular ridges on the mature sepal epidermis, but only a moderate effect on petal cone cell ridges. Using scanning electron microscopy and confocal live imaging combined with quantification of cellular growth, we find that cuticular ridge formation progresses down the sepal from tip to base as the sepal grows, pCUS2：：GFP-GUS reporter expression coincides with cutic- ular ridge formation, descending the sepal from tip to base. Ridge formation also coincides with the reduction in growth rate and termination of cell division of the underlying epidermal cells. Surprisingly, cuticular ridges at first form normally in the cus2 mutant, but are lost progressively at later stages of sepal development, indicating that CUS2 is crucial for the maintenance of cuticular ridges after they are formed~ Our results reveal the dynamics of both ridge formation and maintenance as the sepal grows.