Compositional changes in cell wall polysaccharides from five sweet cherry (Prunus avium L.) cultivars during on-tree ripening.

Excessive softening is a major cause of postharvest deterioration during transportation and storage of fresh cherries. In continuing our studies to identify the factors determining the textural differences between sweet cherry fruit genotypes, we evaluated the solubilization, depolymerization, and monosaccharide composition of pectin and hemicelluloses from five sweet cherry cultivars ('Chelan', 'Sumele', 'Brooks', 'Sunburst', and 'Regina') with contrasting firmness and cracking susceptibility at two developmental stages (immature and ripe). In contrast to what is usually shown in most fruits, cherry softening could occur is some cultivars without marked increases in water-soluble pectin. Although polyuronide and hemicellulose depolymerization was observed in the water-soluble and dilute-alkali-soluble fractions, only moderate association occurs between initial polymer size and cultivar firmness. In all the genotypes the Na2CO3-soluble polysaccharides (NSF) represented the most abundant and dynamic wall fraction during ripening. Firm cultivars showed upon ripening a lower neutral sugars/uronic acid ratio in the NSF, suggesting that they have a lower proportion of highly branched polyuronides. The similar molar ratios of arabinose plus galactose to rhamnose [(Ara+Gal)/Rha] suggest that the cultivars differed in their relative proportion of homogalacturonan (HG) and rhamnogalacturonan I (RG-I) rather than in the size of the RG side chains; with greater proportions of HG in firmer cherries. Ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was useful to identify the depolymerization patterns of weakly bound pectins, but gave less accurate results on ionically bound pectins, and was unable to find any pattern on covalently bound pectins.

Phenolic compounds and vitamins in wild and cultivated apricot (Prunus armeniaca L.) fruits grown in irrigated and dry farming conditions.

BACKGROUND: Turkey is the main apricot producer in the world and apricots have been produced under both dry and irrigated conditions in the country. In this study, phenolic compounds and vitamins in fruits of one wild (Zerdali) and three main apricot cultivars ('Cataloglu', 'Hacihaliloglu' and 'Kabaasi') grown in both dry and irrigated conditions in Malatya provinces in Turkey were investigated. RESULTS: The findings indicated that higher content of phenolic compounds and vitamins was found in apricot fruits grown in irrigated conditions. Among the cultivars, 'Cataloglu' had the highest rutin contents both in irrigated and dry farming conditions as 2855 µg in irrigated and 6952 µg per 100 g dried weight base in dry conditions and the highest chlorogenic acid content in irrigated and dry farming conditions were measured in fruits of 'Hacihaliloglu' cultivar as 7542 µg and 15251 µg per 100 g dried weight base. Vitamin C contents in homogenates of fruit flesh and skin was found to be higher than ß-caroten, retinol, vitamin E and lycopen contents in apricot fruits both in irrigated and dry farming conditions. CONCLUSION: The results suggested that apricot fruits grown in both dry and irrigated conditions had high health benefits phytochemicals and phytochemical content varied among cultivars and irrigation conditions as well. However, more detailed biological and pharmacological studies are needed for the demonstration and clarification of health benefits of apricot fruits.

Deciphering the metabolic pathways influencing heat and cold responses during post-harvest physiology of peach fruit.

Peaches are highly perishable and deteriorate quickly at ambient temperature. Cold storage is commonly used to prevent fruit decay; however, it affects fruit quality causing physiological disorders collectively termed 'chilling injury' (CI). To prevent or ameliorate CI, heat treatment is often applied prior to cold storage. In the present work, metabolic profiling was performed to determine the metabolic dynamics associated with the induction of acquired CI tolerance in response to heat shock. 'Dixiland' peach fruits exposed to 39 °C, cold stored, or after a combined treatment of heat and cold, were compared with fruits ripening at 20 °C. Dramatic changes in the levels of compatible solutes such as galactinol and raffinose were observed, while amino acid precursors of the phenylpropanoid pathway were also modified due to the stress treatments, as was the polyamine putrescine. The observed responses towards temperature stress in peaches are composed of both common and specific response mechanisms to heat and cold, but also of more general adaptive responses that confer strategic advantages in adverse conditions such as biotic stresses. The identification of such key metabolites, which prime the fruit to cope with different stress situations, will likely greatly accelerate the design and the improvement of plant breeding programs.

Phenolic compounds and vitamins in wild and cultivated apricot (Prunus armeniaca L) fruits grown in irrigated and dry farming conditions

BACKGROUND: Turkey is the main apricot producer in the world and apricots have been produced under both dry and irrigated conditions in the country. In this study, phenolic compounds and vitamins in fruits of one wild (Zerdali) and three main apricot cultivars ('Cataloglu', 'Hacihaliloglu' and 'Kabaasi') grown in both dry and irrigated conditions in Malatya provinces in Turkey were investigated. RESULTS: The findings indicated that higher content of phenolic compounds and vitamins was found in apricot fruits grown in irrigated conditions. Among the cultivars, 'Cataloglu' had the highest rutin contents both in irrigated and dry farming conditions as 2855 µg in irrigated and 6952 µg per 100 g dried weight base in dry conditions and the highest chlorogenic acid content in irrigated and dry farming conditions were measured in fruits of 'Hacihaliloglu' cultivar as 7542 µg and 15251 µg per 100 g dried weight base. Vitamin C contents in homogenates of fruit flesh and skin was found to be higher than ß-caroten, retinol, vitamin E and lycopen contents in apricot fruits both in irrigated and dry farming conditions. CONCLUSION: The results suggested that apricot fruits grown in both dry and irrigated conditions had high health benefits phytochemicals and phytochemical content varied among cultivars and irrigation conditions as well. However, more detailed biological and pharmacological studies are needed for the demonstration and clarification of health benefits of apricot fruits.

Transcriptomic profiling during the post-harvest of heat-treated Dixiland Prunus persica fruits: common and distinct response to heat and cold.

Cold storage is extensively used to slow the rapid deterioration of peach (Prunus persica L. Batsch) fruit after harvest. However, peach fruit subjected to long periods of cold storage develop chilling injury (CI) symptoms. Post-harvest heat treatment (HT) of peach fruit prior to cold storage is effective in reducing some CI symptoms, maintaining fruit quality, preventing softening and controlling post-harvest diseases. To identify the molecular changes induced by HT, which may be associated to CI protection, the differential transcriptome of peach fruit subjected to HT was characterized by the differential display technique. A total of 127 differentially expressed unigenes (DEUs), with a presence-absence pattern, were identified comparing peach fruit ripening at 20°C with those exposed to a 39°C-HT for 3 days. The 127 DEUs were divided into four expression profile clusters, among which the heat-induced (47%) and heat-repressed (36%) groups resulted the most represented, including genes with unknown function, or involved in protein modification, transcription or RNA metabolism. Considering the CI-protection induced by HT, 23-heat-responsive genes were selected and analyzed during and after short-term cold storage of peach fruit. More than 90% of the genes selected resulted modified by cold, from which nearly 60% followed the same and nearly 40% opposite response to heat and cold. Moreover, by using available Arabidopsis microarray data, it was found that nearly 70% of the peach-heat responsive genes also respond to cold in Arabidopsis, either following the same trend or showing an opposite response. Overall, the high number of common responsive genes to heat and cold identified in the present work indicates that HT of peach fruit after harvest induces a cold response involving complex cellular processes; identifying genes that are involved in the better preparation of peach fruit for cold-storage and unraveling the basis for the CI protection induced by HT.

Heat treatment of peach fruit: modifications in the extracellular compartment and identification of novel extracellular proteins.

Ripening of peach (Prunus persica L. Batsch) fruit is accompanied by dramatic cell wall changes that lead to softening. Post-harvest heat treatment is effective in delaying softening and preventing some chilling injury symptoms that this fruit exhibits after storage at low temperatures. In the present work, the levels of twelve transcripts encoding proteins involved in cell wall metabolism, as well as the differential extracellular proteome, were examined after a post-harvest heat treatment (HT; 39 °C for 3 days) of "Dixiland" peach fruit. A typical softening behaviour, in correlation with an increase in 1-aminocyclopropane-1-carboxylic acid oxidase-1 (PpACO1), was observed for peach maintained at 20 °C for 3 days (R3). Six transcripts encoding proteins involved in cell wall metabolism significantly increased in R3 with respect to peach at harvest, while six showed no modification or even decreased. In contrast, after HT, fruit maintained their firmness, exhibiting low PpACO1 level and significant lower levels of the twelve cell wall-modifying genes than in R3. Differential proteomic analysis of apoplastic proteins during softening and after HT revealed a significant decrease of DUF642 proteins after HT; as well as an increase of glyceraldehyde-3-phosphate dehydrogenase (GAPC) after softening. The presence of GAPC in the peach extracellular matrix was further confirmed by in situ immunolocalization and transient expression in tomato fruit. Though further studies are required to establish the function of DUF642 and GAPC in the apoplast, this study contributes to a deeper understanding of the events during peach softening and after HT with a focus on this key compartment.

Assessment of Prunus persica fruit softening using a proteomics approach.

Fruit ripening in Prunus persica involves a number of physiological changes, being one of the most significant the mesocarp softening in melting varieties. In order to get a better understanding of the molecular processes involved in this phenomenon, the protein accumulation patterns in firm and soft fruit of three peach and two nectarine melting flesh varieties were assessed using 2D gel analysis. A General Linear Model (GLM) two-way analysis of variance determined that 164 of the 621 protein spots analyzed displayed a differential accumulation associated with the softening process. Among them, only 14 proteins changed their accumulation in all the varieties assessed, including proteins mostly involved in carbohydrates and cell wall metabolism as well as fruit senescence. The analysis among varieties showed that 195 and 189 spots changed within the firm and soft fruit conditions, respectively. Despite the changes in relative abundance in the spot proteins, the proteome is conserved among varieties and during the transition from firm to soft fruit. Only two spots proteins exhibited a qualitative change in all the conditions assessed. These results are in agreement with the notion that Prunus persica commercial varieties have a narrow genetic background.

Metabolic profiling during peach fruit development and ripening reveals the metabolic networks that underpin each developmental stage.

Fruit from rosaceous species collectively display a great variety of flavors and textures as well as a generally high content of nutritionally beneficial metabolites. However, relatively little analysis of metabolic networks in rosaceous fruit has been reported. Among rosaceous species, peach (Prunus persica) has stone fruits composed of a juicy mesocarp and lignified endocarp. Here, peach mesocarp metabolic networks were studied across development using metabolomics and analysis of key regulatory enzymes. Principal component analysis of peach metabolic composition revealed clear metabolic shifts from early through late development stages and subsequently during postharvest ripening. Early developmental stages were characterized by a substantial decrease in protein abundance and high levels of bioactive polyphenols and amino acids, which are substrates for the phenylpropanoid and lignin pathways during stone hardening. Sucrose levels showed a large increase during development, reflecting translocation from the leaf, while the importance of galactinol and raffinose is also inferred. Our study further suggests that posttranscriptional mechanisms are key for metabolic regulation at early stages. In contrast to early developmental stages, a decrease in amino acid levels is coupled to an induction of transcripts encoding amino acid and organic acid catabolic enzymes during ripening. These data are consistent with the mobilization of amino acids to support respiration. In addition, sucrose cycling, suggested by the parallel increase of transcripts encoding sucrose degradative and synthetic enzymes, appears to operate during postharvest ripening. When taken together, these data highlight singular metabolic programs for peach development and may allow the identification of key factors related to agronomic traits of this important crop species.

Proteomic analysis of peach fruit mesocarp softening and chilling injury using difference gel electrophoresis (DIGE).

BACKGROUND: Peach fruit undergoes a rapid softening process that involves a number of metabolic changes. Storing fruit at low temperatures has been widely used to extend its postharvest life. However, this leads to undesired changes, such as mealiness and browning, which affect the quality of the fruit. In this study, a 2-D DIGE approach was designed to screen for differentially accumulated proteins in peach fruit during normal softening as well as under conditions that led to fruit chilling injury. RESULTS: The analysis allowed us to identify 43 spots -representing about 18% of the total number analyzed- that show statistically significant changes. Thirty-nine of the proteins could be identified by mass spectrometry. Some of the proteins that changed during postharvest had been related to peach fruit ripening and cold stress in the past. However, we identified other proteins that had not been linked to these processes. A graphical display of the relationship between the differentially accumulated proteins was obtained using pairwise average-linkage cluster analysis and principal component analysis. Proteins such as endopolygalacturonase, catalase, NADP-dependent isocitrate dehydrogenase, pectin methylesterase and dehydrins were found to be very important for distinguishing between healthy and chill injured fruit. A categorization of the differentially accumulated proteins was performed using Gene Ontology annotation. The results showed that the 'response to stress', 'cellular homeostasis', 'metabolism of carbohydrates' and 'amino acid metabolism' biological processes were affected the most during the postharvest. CONCLUSIONS: Using a comparative proteomic approach with 2-D DIGE allowed us to identify proteins that showed stage-specific changes in their accumulation pattern. Several proteins that are related to response to stress, cellular homeostasis, cellular component organization and carbohydrate metabolism were detected as being differentially accumulated. Finally, a significant proportion of the proteins identified had not been associated with softening, cold storage or chilling injury-altered fruit before; thus, comparative proteomics has proven to be a valuable tool for understanding fruit softening and postharvest.

Biochemical and proteomic analysis of 'Dixiland' peach fruit (Prunus persica) upon heat treatment.

Shipping of peaches to distant markets and storage require low temperature; however, cold storage affects fruit quality causing physiological disorders collectively termed 'chilling injury' (CI). In order to ameliorate CI, different strategies have been applied before cold storage; among them heat treatment (HT) has been widely used. In this work, the effect of HT on peach fruit quality as well as on carbon metabolism was evaluated. When fruit were exposed to 39 degrees C for 3 d, ripening was delayed, with softening inhibition and slowing down of ethylene production. Several differences were observed between fruit ripening at ambient temperature versus fruit that had been heat treated. However, the major effects of HT on carbon metabolism and organoleptic characteristics were reversible, since normal fruit ripening was restored after transferring heated peaches to ambient temperature. Positive quality features such as an increment in the fructose content, largely responsible for the sweetness, and reddish coloration were observed. Nevertheless, high amounts of acetaldehyde and low organic acid content were also detected. The differential proteome of heated fruit was characterized, revealing that heat-induced CI tolerance may be acquired by the activation of different molecular mechanisms. Induction of related stress proteins in the heat-exposed fruits such as heat shock proteins, cysteine proteases, and dehydrin, and repression of a polyphenol oxidase provide molecular evidence of candidate proteins that may prevent some of the CI symptoms. This study contributes to a deeper understanding of the cellular events in peach under HT in view of a possible technological use aimed to improve organoleptic and shelf-life features.

Differential expression of alpha-l-arabinofuranosidase and alpha-l-arabinofuranosidase/beta-d-xylosidase genes during peach growth and ripening.

Arabinose is the major neutral sugar in peach (Prunus persica (L.) Batsch) cell walls and substantial changes in arabinose content take place not only during peach melting, when a rapid-softening-related depolymerizing activity may be expected, but also at the onset of peach ripening. A full-length cDNA clone sequence referred to as PpARF1 (GenBank accession no. DQ486870) was obtained and determined by bioinformatics' analysis to be a peach alpha-l-arabinofuranosidase homologue. The deduced PpARF1 translation product is 677 amino acids in length while the mature protein has a predicted molecular mass of 71.6 kD and a theoretical pI of 4.94. Semi-quantitative RT-PCR reactions were conducted to evaluate the expression of both PpARF1 and PpARF/XYL (GenBank accession no. AB264280), the latter encoding a putative bifunctional protein displaying both alpha-l-arabinofuranosidase and beta-d-xylosidase activities. In peach fruit, the PpARF1 gene expression was detected at every developmental stage with a maximum during S2 (lag phase of development) and a subsequent decrease towards S4 (maximal fruit size). In contrast, PpARF/XYL transcript levels were relatively high at the end of S1 (fruit set) and at S3-E (beginning of the cell expansion). Substantial increases in PpARF1 mRNA levels were found at the beginning and end of the climacteric rise and also in melting fruit. In contrast, PpARF/XYL transcripts reached a maximum when fruit firmness was 22-26 N, with a slight decline during the melting stage. PpARF/XYL and PpARF1 were expressed differently in three fruit tissue types as well as in other plant tissues. Ethylene is regarded as the main regulator of peach ripening and the accumulation of PpARF/XYL and PpARF1 transcripts is coincident with the autocatalytic ethylene production during ripening. On the hand, other factors may also play a role in PpARF1 and PpARF/XYL expression, since transcripts accumulate at different developmental times and organs even when ethylene biosynthesis is barely detectable.

Carbon metabolism of peach fruit after harvest: changes in enzymes involved in organic acid and sugar level modifications.

Peach (Prunus persica L. Batsch) is a climacteric fruit that ripens after harvest, prior to human consumption. Organic acids and soluble sugars contribute to the overall organoleptic quality of fresh peach; thus, the integrated study of the metabolic pathways controlling the levels of these compounds is of great relevance. Therefore, in this work, several metabolites and enzymes involved in carbon metabolism were analysed during the post-harvest ripening of peach fruit cv 'Dixiland'. Depending on the enzyme studied, activity, protein level by western blot, or transcript level by quantitative real time-PCR were analysed. Even though sorbitol did not accumulate at a high level in relation to sucrose at harvest, it was rapidly consumed once the fruit was separated from the tree. During the ripening process, sucrose degradation was accompanied by an increase of glucose and fructose. Specific transcripts encoding neutral invertases (NIs) were up-regulated or down-regulated, indicating differential functions for each putative NI isoform. Phosphoenolpyruvate carboxylase was markedly induced, and may participate as a glycolytic shunt, since the malate level did not increase during post-harvest ripening. The fermentative pathway was highly induced, with increases in both the acetaldehyde level and the enzymes involved in this process. In addition, proteins differentially expressed during the post-harvest ripening process were also analysed. Overall, the present study identified enzymes and pathways operating during the post-harvest ripening of peach fruit, which may contribute to further identification of varieties with altered levels of enzymes/metabolites or in the evaluation of post-harvest treatments to produce fruit of better organoleptic attributes.

Differential expression levels of aroma-related genes during ripening of apricot (Prunus armeniaca L.).

Fruit aroma is a complex trait, particularly in terms of the number of different biosynthetic pathways involved, the complexity of the final metabolites, and their regulation. In order to understand the underlying biochemical processes involved in apricot aroma, four cDNAs (Pa-aat, EU784138; Pa-adhEU395433; Pa-pdcEU395434; and Pa-loxEU439430) encoding an alcohol acyl transferase (AAT), alcohol dehydrogenase (ADH), pyruvate decarboxylase (PDC), and lipoxygenase (LOX), respectively, were isolated and characterized at four stages of maturity in Prunus armeniaca L. cv. Modesto. We observed a reduction in aldehyde and alcohol production between early-harvested fruit and late-harvest fruit, concomitant with an increase in ester production. qPCR analyses showed that the expression levels of the adh gene and the lox gene stayed constant at all stages. Interestingly, aat levels showed a sharp increase in the late-harvest stages concurrent with the changes observed in ester levels. The significance of these changes in relation to aroma production in apricot is discussed.

The population level of Eotetranychus lewisi and the concentration of carbohydrates in peach trees.

Lewis spider mite Eotetranychus lewisi (McGregor) is the most important pest in peach orchards, Prunus persica (L.) (Batsch), in North-Central Mexico. In autumn 2003 and spring 2004, two glasshouse experiments were carried out to assess the influence of that mite on the concentration of total soluble sugars and starch in leaves, bark and roots of 'diamante mejorado' peach trees. Apical leaves of peach trees were inoculated with three mite densities per leaf: (A) 10-20, (B) 21-40, (C) 41-80; a mite-free control was added. In 2003, at 81 days after infestation (DAI), cumulative mite-days per leaf (CMD) were 153, 1313, 2844 and 4771 in control and treatments (A), (B) and (C), respectively. In the same order, these CMD caused reductions in total soluble sugars (TSS): in leaves, 45, 50 and 61%; in bark, 9, 20 and 33%; in roots, 8, 20 and 26%. Reductions of starch concentration in leaves were 17, 43 and 56%; in bark, 25, 55 and 32%; in roots, 17, 22 and 32%. In 2004, at 77 DAI and 57, 1043, 2426 and 3996 CMD for control and treatments (A), (B) and (C), respectively, resulting reductions of TSS were: in leaves, 3, 7 and 15%; in bark, 0.8, 3 and 5%; in roots, 57, 60 and 78%, whereas reductions in starch concentration were: in leaves, 30, 34 and 44%; in bark, 18, 24 and 41%; in roots, 17, 47 and 48%. The higher reductions in roots found in 2004 are attributed to cumulative injury affecting food reserves.