Levels Of Polyphenol Oxidase Research Articles

Characterization of polyphenol oxidase activity in a range of forage ecotypes with different phenol substrates. A new insight for PPO and protein‐bound phenol evaluation

AbstractPlant phenols can influence utilization of forages by ruminants through binding with proteins either by complexing with oxidized phenols (products of polyphenol oxidase activity or formed in oxidizing conditions) or by hydrogen binding with tannins. These protein‐bound phenols (PBPs) affect rumen metabolism by inhibition of both proteolysis and lipolysis. The aim of this work was to assess the level of polyphenol oxidase (PPO) activity (determined with a range of diphenolic substrates), PBP content, and to identify the main source of variation in different forage ecotypes harvested at different phenological stages. PPO activity was strongly influenced by substrate type with a significant effect of forage ecotype. Forage ecotype and phenological stage also influenced PPO and PBP content. PPO showed a strong relationship with dry matter and phenol content of plants.

Role of Achromobacter xylosoxidans AUM54 in Micropropagation of Endangered Medicinal Plant Naravelia zeylanica (L.) DC

This study was carried out to evaluate the inoculation effects of Achromobacterxylosoxidans AUM54 and Indole-3-butyric acid (IBA) on the growth of the medicinal plant Naraveliazeylanica (L.) DC under micropropagation conditions. Results revealed that the micropropagated shoots treated with the combination of endophytic bacterium and IBA promoted shoot growth, root length, number of roots, chlorophyll content, nitrogen content, antioxidant enzymes, and stress tolerance compared with the control plants. A significant increase in shoot fresh and dry weights (64.65 and 8.85 %), root fresh and dry weights (61.65 and 3.91 %), shoot length (30.17 %), root length (28.57 %) and number of roots (276.9 %) was observed in treated plants over controls. Total chlorophyll and nitrogen content of bacterized plants also treated with IBA showed a 48.39 and 116.66 % increase, respectively, compared with controls. A significant increase in peroxidase (22.52 %) and superoxide dismutase levels (48.38 %) and fewer changes in the polyphenol oxidase level were observed in plants treated with A. xylosoxidans AUM54 and IBA. Moreover, stress ethylene levels were reduced by 21.4 and 14.5 % due to bacterization with A. xylosoxidans AUM54 and IBA treatment during postacclimatization and acclimatization stages, respectively. The shoot primordial with application of A. xylosoxidans AUM54 and IBA (1 mg l−1) had increased survivability of N. zeylanica plants by 30 % during the acclimatization stage under greenhouse conditions. From the present study it could be inferred that the association of endophytic bacterium A. xylosoxidans AUM54 and IBA with in vitro shoots of N. zeylanica improved root initiation, promoted plant growth and development under micropropagation conditions, reduced stress ethylene levels, and increased survivability during the postacclimatization stage. Therefore, A. xylosoxidans AUM54 along with IBA treatment can be used as a valuable tool for micropropagation of N. zeylanica and other endangered plants.

Communication between plants: induced resistance in poplar seedlings following herbivore infestation, mechanical wounding, and volatile treatment of the neighbors

AbstractThe possibility of communication between plants was proposed over 25 years ago, although previous demonstrations have suffered from methodological problems and have not been widely accepted. Micromelalopha troglodyta (Graeser) and Clostera anastomosis (L.) (both Lepidoptera: Notodontidae) are important leaf‐feeding insects on poplars (Populus spp.; Salicaceae). There is no report of M. troglodyta‐ or C. anastomosis‐induced plant–plant communication up to now. To understand the regulatory mechanism of poplar defense responses, the specific activities of the presumed anti‐herbivore enzymes phenylalanine ammonia lyase (PAL), lipoxygenase (LOX), polyphenol oxidase (PPO), and peroxidase (POD) were determined in poplar seedlings treated with herbivore infestation and volatiles, artificially damaged seedlings, and intact healthy poplar seedlings growing nearby. The expression levels of PPO, POD, PAL, and LOX were elevated in poplar seedlings treated by herbivore infestation, mechanical wounding, methyl jasmonate, methyl salicylate, or benzothiazole. Furthermore, plants neighboring the treated poplar seedlings also showed increased expression levels of PPO, POD, PAL, and LOX relative to the control. These induced responses against feeding injury, mechanical wounding, and volatile treatment in expression levels of PPO, POD, PAL, and LOX suggest interplant communication between poplar seedlings.

Hard White Versus Hard Red Wheats: Taste Tests and Milling and Baking Properties

ABSTRACTMolecular markers for the red grain color (R) loci controlling seed color and the polyphenol oxidase (Ppo‐A1) locus controlling polyphenol oxidase (PPO) activity in seed have recently been developed. These markers provided the opportunity to convert the hard red spring wheat cultivars Choteau and Hank to white‐seeded versions with high and low PPO levels, respectively. These sets of near‐isogenic lines provided material to test the effects of seed color and PPO activity on a range of end‐use quality traits. We tested recurrent parents Choteau and Hank, along with near‐isogenic derivatives with white seed, in two replicated trials in Bozeman, Montana, for end‐use quality parameters. The white‐seeded lines consisted of both high‐ and low‐PPO near‐isogenic lines. The primary impact of white seed was the production of whole wheat bread with a perceived sweeter taste relative to the red‐seeded lines. Noodle color was not consistently impacted by the level of PPO variation despite relatively large reductions in PPO level. The alleles for white seed color did not appear to impact agronomic traits. These results suggested that hard white low‐PPO hard spring wheat would be advantageous in terms of conferring brighter color to Asian noodles and a sweeter taste to whole wheat bread.

Enzyme activity in wheat breeding lines derived from matings of low polyphenol oxidase parents

Polyphenol oxidase (PPO) in grain plays a major role in time-dependent discoloration of wheat (Triticum aestivum L.) products, especially fresh noodles. Breeding wheat cultivars with low or nil PPO activity can reduce undesirable product darkening. The low PPO line PI 117635 was crossed to two low PPO wheats, IDO580 and ‘IDO377s’, to determine whether matings between wheats with low levels of grain PPO would result in complementation, such that lines with still lower or nil PPO would be generated. Progeny in a population derived from PI 117635/IDO580 displayed no variation in PPO activity. In the F3:4 populations derived from PI 117635/IDO377s, and the reciprocal IDO377s/PI 117635, normal distributions of low to high PPO activity were observed. Field-grown populations (F3:5; F3:6) derived from IDO377s crosses were analyzed for PPO activity and used to determine whether lines with nil PPO activity were generated. Of 239 lines, 154 were verified to have PPO activity that was not significantly different from the low PPO durum (Triticum turgidum var durum) cultivar ‘Ben’. PCR analysis showed that the populations were fixed for a putative low PPO allele at Ppo-A1. Using markers for Ppo-D1, it was found that the average PPO activity of lines with 490 bp PCR fragments from PPO29 was significantly lower than that of lines with 560 bp fragments from STS01. These results disagreed with that predicted from previous reports for markers for Ppo-D1 alleles. Thus, breeders should exercise caution when making selections using markers for alleles at Ppo-D1, as known markers might predict erroneous phenotypes and genotypes in some wheat backgrounds.

Registration of ‘Anton’ Hard White Winter Wheat

Low levels of the grain enzyme polyphenol oxidase (PPO) are a necessary attribute of any newly developed hard white wheat (Triticum aestivum L.) adapted to the Great Plains. Low PPO correlates with enhanced end‐use quality, including the final product color in noodle applications. Few wheats with this necessary characteristic presently are available. The objective of this study was to develop a hard winter wheat adapted to the region that possesses both low levels of grain PPO and quality characteristics that would allow its utilization in domestic bread‐making applications. This goal was achieved via the development and release in December 2007 of ‘Anton’ (Reg. No. CV‐1057, PI 651044) hard white winter wheat by the USDA‐ARS and the Nebraska Agricultural Experiment Station. Anton was released primarily for its low levels of PPO. Flour‐PPO levels of Anton (tested under the experimental designation NW98S097) were significantly lower than all other entries in the 2003 and 2004 USDA‐ARS coordinated Northern Regional Performance nursery. Polyphenol oxidase levels of Anton in grain from the 2005 University of Nebraska cultivar performance trials were not significantly different from those of the low‐PPO cultivar ‘Platte’ and were significantly lower than those of several additional current hard white winter wheat cultivars and breeding lines. Anton was selected from the cross WA691213‐27/N86L177//Platte.

Effects of Lymantria dispar feeding and mechanical wounding on defense-related enzymes in Populus simonii × Populus nigra

In plants, lipoxygenase (LOX) and polyphenol oxidase (PPO) have been related to defense mechanisms against insect feeding and wounding and these roles were investigated in poplar ( Populus simonii × Populus nigra ) regarding induction by third-instar Lymantria dispar larvae feeding and punching mechanical wounding. The results showed that L. dispar feeding and mechanical wounding caused different responses of protein and transcript levels of LOX and PPO. PPO was obviously induced by L. dispar feeding during a 72 h period, while LOX was not significantly induced by L. dispar feeding. For mechanical wounding, activity and mRNA expression level of LOX and PPO were not significantly induced but were mostly inhibited. Therefore, LOX was not involved in defensive mechanisms of P. simonii × P. nigra . The PPO gene may be significantly related to poplar defense against L. dispar attack. Key words: Lipoxygenase, polyphenol oxidase, Populus simonii × Populus nigra, Lymantria dispar feeding, mechanical wounding.

Induction of resistance in cucumber against seedling damping-off by plant growth-promoting rhizobacteria (PGPR) Bacillus megaterium strain L8

Bacillus megaterium L8, a plant growth-promoting rhizobacterium (PGPR), was isolated and evaluated for its ability to induce resistance in cucumber against seedling damping-off caused by Pythium aphanidermatum . Root-splitting challenge experiments showed that L8 treatment of cucumber roots more effectively suppressed seedling damping-off than did the control as judged by seedling survival rate (83.45 versus 31.68% at 28 days), indicating that strain L8 is capable of inducing systemic disease resistance in cucumber. To explore the potential mechanism underlying the induced systemic resistance (ISR) mediated by L8, the expression profile of several plant defense-related enzymes: superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) were monitored in the roots treated with L8 or P. aphanidermatum and untreated leaves in a time course of 13 days. Levels of SOD, POD, CAT, PPO and PAL activities in the treated roots and untreated leaves of cucumber seedlings were all significantly higher as compared with the control and respectively peaked in the roots at 3, 3, 5, 5 and 5 days and correspondingly in the leaves at 5, 3, 5, 5 and 5 days post-inoculation. The enhanced expression patterns of the above enzymes following L8 or P. aphanidermatum treatment suggested that systemic induction of plant defense enzymes by L8 might account for its ability to provide effective protection for cucumber from seedling damping-off caused by the soil-borne fungal pathogen P. aphanidermatum.

Divergent Selection for Polyphenol Oxidase and Grain Protein and Their Impacts on White Salted Noodle, Bread, and Agronomic Traits in Wheat

Consumers prefer noodles with a bright creamy color that maintains with time. High levels of polyphenol oxidase (PPO) activity and high flour protein are associated with darker noodles. A major gene on chromosome 2A in wheat controls substantial variation in PPO activity. Our goal was to determine the impact of selecting for Ppo‐A1 allelic differences and high vs. low protein on white salted noodle, bread, and agronomic traits. Two winter wheat (Triticum aestivum L.) populations were created that segregated for grain protein concentration and for Ppo‐A1a (high PPO) and Ppo‐A1b (low PPO). Four selection populations were created by divergent selection for grain protein, followed by selection of Ppo‐A1a and Ppo‐A1b alleles within the high and low grain protein groups. The selection populations were evaluated in replicated trials in two environments. White salted noodle and bread quality and agronomic traits were measured using four lines from each selection population. The Ppo‐A1a vs. Ppo‐A1b classes differed by 0.40 ΔA475 min−1 g−1 and the high‐ vs. low‐protein classes differed by 17 g kg−1 in grain protein. The high‐protein class yielded 8.6% less than the low‐protein group. Ppo‐A1 allelic class had no affect on agronomic traits. High‐protein class gave higher loaf volume, but Ppo‐A1 allelic class difference did not affect bread quality. Ppo‐A1 allelic class did not affect noodle brightness (L*) at 0 or 24 h, but Ppo‐A1a class showed greater change in L* with time. High protein gave darker noodles at both 0 and 24 h and greater change in L* with time. Ppo‐A1 allelic class did not affect noodle texture, but noodles were more firm with high protein compared with low protein. Ppo‐A1 allelic class and protein effects on noodle and bread traits were additive.

Impact of Protein on Darkening in Yellow Alkaline Noodles

Darkening in yellow alkaline noodles (YAN) was examined over a 24 h period in noodles made from 4 wheat varieties, including varieties with different levels of polyphenol oxidase (PPO) activity, selected to cover a range of protein levels. Noodles were made in the presence and absence of the PPO inhibitor, tropolone. The darkening was divided into two time periods: 0-4 h and 4-24 h. The first four hours was described by a composite rate equation, and this period was subdivided into two stages. The rate of darkening in the first stage was independent of both protein concentration and PPO activity. The amount of darkening (c), however, was highly dependent on protein concentration during this stage (-tropolone, r = 0.902; +tropolone, r = 0.905), but independent of PPO activity. The first stage darkening was a zero order reaction where additional protein does not increase the reaction rate, but when the protein supply has been depleted, the reaction stops. The rate of darkening during the first stage (k'(1) = 5.6 +/- 1.0) was similar to the rate of change in the protein structure (k'(1) = 6.5 +/- 1.3) as measured using the amide II band by infrared spectroscopy. This suggested that the first stage of darkening represents changes in light reflectance and absorbance caused by changes in hydrogen bonding rather than changes in covalent bonding. During the second stage of darkening, both the rate (k'(2)) and amount of darkening (DeltaL*(4h-c)) were significantly correlated with protein concentration (-tropolone, r = 0.465; +tropolone, r = 0.813), and in the absence of tropolone the amount of darkening was increased by PPO activity. The amount of darkening (DeltaL*(24h-4h)) during the second time period (4-24 h) (or third stage) was significantly correlated in the presence of tropolone (r = 0.375) and in the absence of tropolone (r = 0.428) with protein concentration. However, compared with earlier stages the response of non-PPO darkening during the third stage to change in protein concentration was smaller. Protein oxidation, or more specifically oxidation of tyrosine groups within the protein, appears to be the main mechanism involved in non-PPO darkening in YAN during the second and third stages with glutenin being the main reactant. Albumin and globulin are important substrates for PPO. No differences in darkening were detected in YAN made from the four varieties in the presence of tropolone; however, differences in YAN darkening were observed for the second and third stages due to site and year variation.

Studies on Polyphenol Oxidase Activity of Heat Stabilized Whole Wheat Flour and its Chapatti Making Quality

Studies were conducted to evaluate the effect of heat treatment on polyphenol oxidase (PPO) activity of whole-wheat flour (WWF) as well as its chapatti making quality. Whole wheat flour samples were heat treated through various means such as (i) dipping in boiling water (BW) for 20, 30, 40, 50, and 60 min; (ii) inpack heating under pressure (PH) at 0.352 kg/cm2 for 4, 6, 8, 10, and 12 min; (iii) microwave heat treatment (MW) at 900 Watt, 2450 MHz for 20, 40, 60, 80, and 100 s. Studies showed that the heat treatment effectively reduced PPO level in whole wheat flour; although, it had adverse effect on the dough-making quality. Based on textural analysis of dough and chapatti as well as sensory scores of chapatti, the conditions for each of the treatments were optimized, i.e., (i) Dipping in boiling water (BW) for 30 min; (ii) inpack heating under pressure (PH) at 0.352 kg/cm2 for 10 min; and (iii) microwave heating (MW) for 80 s. A maximum reduction (71.2%) in PPO activity of WWF using microwave treatment could be achieved followed by PH (56.9%) and BW (38.3%). The changes in colour of unbaked chapattis (flattened circular dough, diameter 150.0 mm and thickness 2.0 mm) and changes in quality of baked chapattis were measured to assess the effectiveness of the heat treatment. The L-value (lightness) decreased from 65.2 to 55.8, 65.7 to 58.3, 65.9 to 61.4, and 64.8 to 49.1 in case of BW, PH, MW treated, and control samples, respectively during the 72 h of storage under refrigeration temperature (5–6°C).

CHANGES IN CHEMICAL CONSTITUENTS AND POLYPHENOL OXIDASE ACTIVITY OF TEA LEAVES WITH SHOOT MATURITY AND COLD STORAGE

ABSTRACT The variation in the composition of fresh tea leaves with season and shoot maturity, and to the applicability of cold storage (4C and 90% relative humidity [RH]) for the purpose of withering of tea leaves were studied. The results showed that the levels of polyphenol oxidase (PPO) activity and the polyphenolic content changed significantly with plucking season and shoot maturity. No significant difference was observed between the total polyphenolic content of the cold storage-withered and traditionally withered samples, whereas the loss of PPO activity was less in the cold-stored leaves. No significant difference was observed between the cold storage-withered and traditionally withered samples in terms of the end product quality. Results showed that cold storage at 4C and at 90% RH was suitable for storing fresh leaves after plucking until the time of processing and it is possible to achieve withering during the cold storage of tea leaves. PRACTICAL APPLICATIONS The tea growing season is very short in Turkey. Therefore, the tea processing factories sometimes experience capacity problems, and high amounts of tea leaves are lost because of poor storage conditions until the time of processing. Moreover, the quality losses in fresh tea leaves between the time of harvesting and processing have a negative impact on the final black tea quality. The application of cold storage for long-term withering of fresh tea leaves can help to prevent the postharvest losses and can prolong the period for black tea production.

Effect of Different Packaging Films on Postharvest Quality and Selected Enzyme Activities of Hypsizygus marmoreus Mushrooms

Freshly harvested Hypsizygus marmoreus mushrooms were packaged using different packaging films, and physiological changes associated with postharvest deterioration, together with the activities of selected enzymes thought to play a role in senescence, were monitored during subsequent storage for 16-24 days at 4 degrees C and 65-70% relative humidity. A biaxially oriented polypropylene film (BOPP) maintained the postharvest appearance of the mushrooms most effectively by significantly reducing the incidence of unsightly aerial hyphae on the pileal surface and restricting mushroom softening. These samples also exhibited smaller initial decreases in soluble protein, smaller increases in reducing sugar content, and lower levels of malondialdehyde accumulation during early storage. Smallest increases in proteinase activity were recorded in samples wrapped with BOPP and polyoletin packaging, and superoxide dismutase and polyphenol oxidase levels were significantly higher and lower, respectively, in the former. Choice of packaging can significantly affect postharvest quality loss in H. marmoreus and improve mushroom shelf life.

Characterisation and tissue distribution of polyphenol oxidase of deepwater pink shrimp ( Parapenaeus longirostris)

Characterisation and tissue distribution of polyphenol oxidase (PPO) was studied in deepwater pink shrimp ( Parapenaeus longirostris) post mortem. PPO activity was the highest in the carapace, followed by that in the abdomen exoskeleton, cephalotorax, pleopods and telson. No PPO activity was found in the abdomen muscle and in the pereopods and maxillipeds using the enzymatic assay. Storage of whole shrimps and of the different organs showed that melanosis (blackening) required the presence of the cephalotorax to be initiated, indicating that its development depends on other factors in addition to the PPO levels. Further characterisation was carried out in extracts partly purified using 40–70% ammonium sulfate fractionation. The enzyme had the highest activity at pH 4.5 and was most stable at pH 4.5 and 9.0. No clear maximum was observed in the 15–60 °C range but the higher stability was achieved at 30–35 °C. Apparent kinetic constants in the partly purified PPO from carapace were K M = 1.85 mM and V max = 38.5 U/mg of protein, pointing to a high affinity and reactivity of the enzyme when assayed with DOPA. Electrophoretic mobility was studied in native PAGE and non-reducing SDS–PAGE followed by staining with DOPA. Approximate MW of 500 kDa and 200 kDa were observed, respectively. These two forms could correspond to aggregates of minor PPO subunits that could not be resolved in these electrophoretic systems. The peptide mass fingerprinting obtained by MALDI-TOF analysis showed some peptides whose homology with hemocyanins and different PPO subunit precursors has already been demonstrated in the same species.

Latent and Active Polyphenol Oxidase (PPO) in Red Clover (Trifolium pratense) and Use of a Low PPO Mutant To Study the Role of PPO in Proteolysis Reduction

Polyphenol oxidase (PPO) activity in leaf extracts of wild type (WT) red clover and a mutant line expressing greatly reduced levels of PPO (LP red clover) has been characterized. Both latent and active forms of PPO were present, with the latent being the predominant form. PPO enzyme and substrate (phaselic acid) levels fluctuated over a growing season and were not correlated. Protease activation of latent PPO was demonstrated; however, the rate was too low to have an immediate effect following extraction. A novel, more rapid PPO activation mechanism by the enzyme's own substrate was identified. Rates of protein breakdown and amino acid release were significantly higher in LP red clover extracts compared with WT extracts, with 20 versus 6% breakdown of total protein and 1.9 versus 0.4 mg/g FW of free amino acids released over 24 h, respectively. Inclusion of ascorbic acid increased the extent of protein breakdown. Free phenol content decreased during a 24 h incubation of WT red clover extracts, whereas protein-bound phenol increased and high molecular weight protein species were formed. Inhibition of proteolysis occurred during wilting and ensilage of WT compared with LP forage (1.9 vs 5 and 17 vs 21 g/kg of DM free amino acids for 24 h wilted forage and 90 day silage, respectively). This study shows that whereas constitutive red clover PPO occurs predominantly in the latent form, this fraction can contribute to reducing protein breakdown in crude extracts and during ensilage.

Control of pink discoloration in coconut water

The pink discoloration in coconut water is a result of the initial enzymatic action of polyphenol oxidase (PPO) on the phenolic substrates which are naturally present in the product. Activity of the enzyme is further enhanced by metal contamination such as copper and exposure of the product to high temperature during its processing and storage.
 The optimum copper concentration to initiate pinking in coconut water was established at 3.96 x 10-04 mM. The PPO level was also shown to vary among coconut varieties and ages. When subjected to optimum conditions for enzymatic activity, the water from younger nuts (7-8 months old) went pink while mature nuts (9-10 months old) showed no discoloration. Application of food-grade resins to remove the phenolic substrates in coconut water was deemed as a possible solution to prevent the discoloration. Further testing in this area needs to be done.

Limited impact of elevated levels of polyphenol oxidase on tree-feeding caterpillars: assessing individual plant defenses with transgenic poplar

Polyphenol oxidase (PPO) is commonly believed to function as an effective antiherbivore defense in plants. PPO is induced in plants following herbivory, and insect performance is often negatively correlated with PPO levels. However, induced defenses create numerous changes in plants, and very little work has been done to test the direct effects of PPO on insect herbivores separately from other changes. This study examined the impacts of high levels of PPO on the performance of two species of tree-feeding caterpillars (Lymantria dispar and Orgyia leucostigma) on poplar. Transgenic PPO-overexpressing poplar (Populus tremula x Populus alba) was used as a source of elevated-PPO leaves, thereby controlling for the multiple effects of induction. In addition, the impacts of treating poplar foliage with high levels of purified mushroom PPO were examined on the two caterpillar species. Contrary to expectation, in several cases increased PPO levels had no significant effect on insect consumption or growth rates. Although one of the mechanisms by which PPO is believed to impact herbivores is via increased oxidative stress, the ingestion of large amounts of PPO had little or no effect on semiquinone radical and oxidized protein levels in the gut contents of lymantriid caterpillars. PPO activity in caterpillars is likely limited by the low oxygen and high ascorbate levels commonly found in their gut contents. This study questions whether induced PPO functions as an effective post-ingestive defense against tree-feeding caterpillars, and indicates that controlled, mechanistic studies are needed in other plant-herbivore systems to test for a direct effect of PPO on insect performance.

Red clover polyphenol oxidase reduces ruminal lipolysis in in vitro batch culture

It has been shown that the rate of lipolysis and proteolysis differs significantly between red clover genotypes with different levels of polyphenol oxidase (PPO) activity (Lee et al. 2004). Sullivan and Hatfield, (2006) reported the development of genetically modified isolines of red clover with the PPO1 gene silenced. This material was used to examine the role of the red clover PPO enzyme on lipolysis and ultimately C18 polyunsaturated fatty acid biohydrogenation in batch culture. If the role of PPO in reducing ruminal lipolysis of plant lipids is proven it would influence breeding strategies for forages which exhibit this trait in an attempt to increase the levels of beneficial PUFA and decrease detrimental trans and saturated fatty acids in animal products.

Chemical Changes and Overexpressed Genes in Sweet Basil (Ocimum basilicumL.) upon Methyl Jasmonate Treatment

The effects of methyl jasmonate (MeJA) on the production of bioactive chemicals and gene expression in sweet basil were investigated. The total amount of phenolic compounds significantly increased in sweet basil after 0.5 mM MeJA treatment. Among the phenolic compounds, rosmarinic acid (RA) and caffeic acid (CA) were identified, and their amounts increased by 55 and 300%, respectively. The total amount of terpenoids also significantly increased after the same treatment. Particularly, eugenol and linalool increased by 56 and 43%, respectively. To better understand the signaling effect of MeJA on sweet basil, suppression subtractive hybridization (SSH) was used to identify the MeJA up-regulated genes. Among the 576 cDNA clones screened from the forward SSH cDNA library, 28 were found to be up-regulated by the MeJA treatment. Sequencing of these cDNA clones followed by BLAST searching revealed six unique transcripts displaying high similarities to the known enzymes and peptide, that is, lipoxygenase (LOX), cinnamic acid 4-hydroxylase (C4H), prephenate dehydrogenase (PDH), polyphenol oxidase (PPO), acid phosphatase (APase), and pentatricopeptide repeat (PPR), which play significant roles in the formation of secondary metabolites in sweet basil. Northern blot further confirmed the increased production at transcriptional level of LOX, C4H, PDH, PPO, PPR, and APase.

Ripening‐related changes in the cell walls of olive (Olea europaea L.) pulp of two consecutive harvests

AbstractOlive fruits, harvested in two consecutive seasons at green, cherry and black stages, were used to study compositional changes in the cell walls during ripening. Ripening‐related changes in both harvests were characterised mainly by an increase in the solubilisation of pectic and hemicellulosic polysaccharides, an increase in the relative amount of arabinose in pectic polysaccharides and a decrease in the degree of methylesterification of pectic polysaccharides. Further to degrading processes, the data obtained suggest the synthesis of new polysaccharides. The analysis of olive cell wall phenolics showed mainly the presence of p‐coumaric acid, which increased in one harvest, whereas in the other the values did not differ. The samples of the second harvest, although presenting green, cherry and black colours, had less distinct ripening characteristics than those of the previous harvest. Different activity levels of polyphenol oxidase, polygalacturonase and pectin methylesterase might have contributed to the differences observed between the two harvests. The results showed the distinct extension of ripening‐related changes in the cell walls of the two harvests, indicating that the olive colour, although characteristic of the stage of ripening, cannot be strictly used for its evaluation and definition. Copyright © 2006 Society of Chemical Industry