Caroline Orfila

ARABINAN DEFICIENT 1 Is a Putative Arabinosyltransferase Involved in Biosynthesis of Pectic Arabinan in Arabidopsis

The function of a putative glycosyltransferase (At2g35100) was investigated in Arabidopsis (Arabidopsis thaliana). The protein is predicted to be a type 2 membrane protein with a signal anchor. Two independent mutant lines with T-DNA insertion in the ARABINAN DEFICIENT 1 (ARAD1) gene were analyzed. The gene was shown to be expressed in all tissues but particularly in vascular tissues of leaves and stems. Analysis of cell wall polysaccharides isolated from leaves and stems showed that arabinose content was reduced to about 75% and 46%, respectively, of wild-type levels. Immunohistochemical analysis indicated a specific decrease in arabinan with no change in other pectic domains or in glycoproteins. The cellular structure of the stem was also not altered. Isolated rhamnogalacturonan I from mutant tissues contained only about 30% of the wild-type amount of arabinose, confirming the specific deficiency in arabinan. Linkage analysis showed that the small amount of arabinan present in mutant tissue was structurally similar to that of the wild type. Transformation of mutant plants with the ARAD1 gene driven by the 35S promoter led to full complementation of the phenotype, but none of the transformants had more arabinan than the wild-type level. The data suggest that ARAD1 is an arabinan α-1,5-arabinosyltransferase. To our knowledge, the identification of other l-arabinosyltransferases has not been published.

Loss-of-Function Mutation of REDUCED WALL ACETYLATION2 in Arabidopsis Leads to Reduced Cell Wall Acetylation and Increased Resistance to Botrytis cinerea

Nearly all polysaccharides in plant cell walls are O-acetylated, including the various pectic polysaccharides and the hemicelluloses xylan, mannan, and xyloglucan. However, the enzymes involved in the polysaccharide acetylation have not been identified. While the role of polysaccharide acetylation in vivo is unclear, it is known to reduce biofuel yield from lignocellulosic biomass by the inhibition of microorganisms used for fermentation. We have analyzed four Arabidopsis (Arabidopsis thaliana) homologs of the protein Cas1p known to be involved in polysaccharide O-acetylation in Cryptococcus neoformans. Loss-of-function mutants in one of the genes, designated REDUCED WALL ACETYLATION2 (RWA2), had decreased levels of acetylated cell wall polymers. Cell wall material isolated from mutant leaves and treated with alkali released about 20% lower amounts of acetic acid when compared with the wild type. The same level of acetate deficiency was found in several pectic polymers and in xyloglucan. Thus, the rwa2 mutations affect different polymers to the same extent. There were no obvious morphological or growth differences observed between the wild type and rwa2 mutants. However, both alleles of rwa2 displayed increased tolerance toward the necrotrophic fungal pathogen Botrytis cinerea.

Making and using antibody probes to study plant cell walls

The cell wall is a structurally complex and highly varied domain at the surface of all plant cells. Emerging knowledge of the dynamic molecular nature of cell walls and their possible participation in developmental processes has increased awareness of their contribution to the creation and maintenance of plant form. The molecular architecture of plant cell walls is based to a large extent on carbohydrates and phenolics. Technologies for direct functional analyses of these often multi-functional components are not readily available and thus defined antibodies are powerful tools to gain insight into the spatial and developmental aspects of cell wall structure and function. This review discusses aspects of monoclonal antibody preparation, including phage display technology. The challenges of making defined antibodies relevant to plant cell walls are discussed along with current and future requirements for antibodies. The use of defined antibodies is discussed in the context of a range of approaches and techniques that demonstrate the important contribution that antibodies can make to the understanding of cell wall structure, organisation, developmental dynamics and function.

Determination of amygdalin in apple seeds, fresh apples and processed apple juices

Cyanogenic glycosides are natural plant toxicants. Action by endogenous plant enzymes can release hydrogen cyanide causing potential toxicity issues for animals including humans. We have quantified amygdalin in seeds from different apple varieties, determined the effects of processing on the amygdalin content of apple juice and quantified amygdalin in commercially-available apple juices. Amygdalin contents of seeds from fifteen varieties of apples ranged from 1 mg g(-1) to 4 mg g(-1). The amygdalin content of commercially-available apple juice was low, ranging from 0.01 to 0.04 mg ml(-1) for pressed apple juice and 0.001-0.007 mg ml(-1) for long-life apple juice. Processing led to juice with low amygdalin content, ranging from 0.01 mg ml(-1) to 0.08 mg ml(-1). The results presented show that the amygdalin contents of commercially-available apple juices are unlikely to present health problems to consumers.

Expression of mung bean pectin acetyl esterase in potato tubers: effect on acetylation of cell wall polymers and tuber mechanical properties

A mung bean (Vigna radiata) pectin acetyl esterase (CAA67728) was heterologously expressed in tubers of potato (Solanum tuberosum) under the control of the granule-bound starch synthase promoter or the patatin promoter in order to probe the significance of O-acetylation on cell wall and tissue properties. The recombinant tubers showed no apparent macroscopic phenotype. The enzyme was recovered from transgenic tubers using a high ionic strength buffer and the extract was active against a range of pectic substrates. Partial in vivo de-acetylation of cell wall polysaccharides occurred in the transformants, as shown by a 39% decrease in the degree of acetylation (DA) of tuber cell wall material (CWM). Treatment of CWM using a combination of endo-polygalacturonase and pectin methyl esterase extracted more pectin polymers from the transformed tissue compared to wild type. The largest effect of the pectin acetyl esterase (68% decrease in DA) was seen in the residue from this extraction, suggesting that the enzyme is preferentially active on acetylated pectin that is tightly bound to the cell wall. The effects of acetylation on tuber mechanical properties were investigated by tests of failure under compression and by determination of viscoelastic relaxation spectra. These tests suggested that de-acetylation resulted in a stiffer tuber tissue and a stronger cell wall matrix, as a result of changes to a rapidly relaxing viscoelastic component. These results are discussed in relation to the role of pectin acetylation in primary cell walls and its implications for industrial uses of potato fibres.

Interaction of hydroxycinnamic acids and their conjugates with organic anion transporters and ATP‐binding cassette transporters

SCOPE Hydroxycinnamic acids are abundant antioxidants in our diet. In humans, hydroxycinnamic acids are metabolized to form sulfates and glucuronides, with the majority recovered in urine. METHODS AND RESULTS We assessed the potential roles of organic anion transporters (OATs) and ATP-binding cassette (ABC) transporters in the renal uptake and efflux of hydroxycinnamic acid conjugates. Uptake studies using OAT1 (SLC22A6)-, OAT2 (SLC22A7)-, and OAT3 (SLC22A8)-expressing 293H embryonic kidney cells showed that OAT1 and OAT3, but not OAT2, accepted hydroxycinnamic acid conjugates as substrates. OAT1 and OAT3 mediated the basolateral uptake of hydroxycinnamic acid sulfates and glucuronide conjugates, respectively. Hydroxycinnamic acid sulfates are substrates of OAT4 and were capable of trans-stimulating 5-carboxyfluorescein uptake mediated by OAT4. On the other hand, hydroxycinnamic acid conjugates are not substrates for the ABC transporters, multidrug resistance protein 2 (MRP2/ABCC2) or breast cancer resistance protein (BCRP/ABCG2), demonstrated by the inability to alter ATPase activity. Cis-inhibition studies with OATs and MRPs revealed that hydroxycinnamic acid conjugates have limited impact on the transport of model substrates significantly at physiological concentrations. CONCLUSION Concerted action of OAT1, OAT3, and OAT4 is involved in the elimination of hydroxycinnamic acid conjugates into urine, whereas MRP2 and breast cancer resistance protein are not involved in the disposition of these conjugates.

Sequence analysis and characterization of a novel pectin acetyl esterase from Bacillus subtilis

A recombinant pectin acetyl esterase (YxiM) from Bacillus subtilis was characterised and the enzymatic properties compared to previously characterised pectin acetyl esterases (PAE’s). The YxiM protein had a pH optimum of 8.0 and was stable above pH 4.O. The enzyme released acetate from pectin isolated from different sources and from various synthetic compounds. In addition, YxiM showed a preference for acetylated tobacco homogalacturonan oligomers. Determination of the kinetic constants of YxiM indicated that the enzyme had a higher affinity to acetylated substrates, but a lower specific activity towards these substrates than PaeY from Erwinia chrysanthemi. Pre-treatment of sugar beet pectin with pectin methyl esterase (PME) from Aspergillus aculeatus increased the ability of YxiM to release acetate and similarly, pre-treatment with YxiM increased the ability of PME to release methanol. This demonstrates that YxiM acts in synergy with PME on the modification of plant cell wall pectin.

Inhibitory effect of chlorogenic acid on digestion of potato starch

The effect of the chlorogenic acid isomer 5-O-caffeoylquinic acid (5-CQA) on digestion of potato starch by porcine pancreatic alpha amylase (PPAA) was investigated using isolated starch and cooked potato tuber as substrates. In vitro digestion was performed on five varieties of potato with varying phenolic content. Co- and pre-incubation of PPAA with 5-CQA significantly reduced PPAA activity in a dose dependent manner with an IC50 value of about 2mgmL(-1). Lineweaver-Burk plots indicated that 5-CQA exerts a mixed type inhibition as km increased and Vmax decreased. The total polyphenol content (TPC) of peeled tuber tissue ranged from 320.59 to 528.94mg 100g(-1)dry weight (DW) in raw tubers and 282.03-543.96mg 100g(-1)DW in cooked tubers. With the exception of Désirée, TPC and 5-CQA levels decreased after cooking. Principle component analysis indicated that digestibility is affected by multiple factors including phenolic, dry matter and starch content.

Development and application of an enzyme-linked immunosorbent assay (ELISA) for the quantification of amygdalin, a cyanogenic glycoside, in food.

Amygdalin is a member of the cyanogenic glycoside group of plant secondary metabolites capable of generating hydrogen cyanide under certain conditions. As a consequence, the cyanogenic glycosides have been associated with incidents of acute and subacute food poisoning. Specific antibodies were raised against an amygdalin-bovine serum albumin immunogen synthesized using a novel approach. The antibodies were used in a microtitration plate enzyme-linked immunosorbent assay (ELISA) for the quantification, for the first time, of amygdalin in commercially available foods. Correlation of results with high-performance liquid chromatography was very high (r = 0.983). The limit of detection of the immunoassay was 200 ± 0.05 pg mL(-1), and the 50% inhibitory concentration of amygdalin was 50 ± 0.02 ng mL(-1), making the ELISA particularly sensitive.

Enrichment of Biscuits with Matcha Green Tea Powder: Its Impact on Consumer Acceptability and Acute Metabolic Response

Matcha green tea powder (MGTP) is made with finely ground green tea leaves that are rich in phytochemicals, most particularly catechins. Shortbread biscuits were enriched with MGTP and evaluated for consumer acceptability and potential functional health properties. Baking decreased the content of total catechins by 19% compared to dough, although epimerization increased the amount of (+)-gallocatechin gallate at the expense of other catechins such as (−)-epigallocatechin gallate. Consumer acceptability tests using a 9-point hedonic scale showed that consumers preferred enriched biscuits with low content of MGTP (2 g of MGTP 100 g−1 of flour), and an increase of sugar content did not significantly improve the acceptability of MGTP-enriched biscuits. Overall, enrichment of biscuits with MGTP did not significantly affect the postprandial glucose or triglyceride response (area under curve) compared to non-enriched biscuits consumed with water or MGTP drink. Enriching biscuits with Matcha green tea is acceptable to consumers, but may not bring significant postprandial effects.