An immunohistochemical study of the compartmentation of metabolism during the development of grape (Vitis vinifera L.) berries

The comparison of biochemical composition of Actinidia kolomikta and Actinidia polygama fruits

The demand for natural products, which are rich in biologically active compositions, grows constantly. The choice and production of such products can minimize the deficit of importance for human organism components, which are contained only in plant food. The paper contains the laboratory studying results of the chemical composition of the fruits of two Actinidia Lindl. cultivars of Federal State Budgetary Scientific Institution Federal Horticultural Research Center for Breeding, Agrotechnology, and Nursery (FSBSI FSC for Horticulture) genetic collection: Actinidia kolomikta (Rupr. et Maxim.) Maxim. and Actinidia polygama (Siebold et Zucc.) Maxim. All the presented samples are grown in field conditions. The fruits were picked up in the phase of harvest maturity while ripening. The data on antioxidant activity of water and methanol extracts, the content of phenolic compounds sum, soluble solids, and titratable acids in the fruits, and on qualitative composition of secondary metabolites (organic acids, fatty acids, mono-, di- and polysaccharides) are given in the paper. The variation limits of the parameters under study depending on the sample are presented. As a result of the laboratory studies, it was stated that A. kolomikta fruits 10 times exceed A. polygama fruits on all the stated parameters. Only the results on the soluble solids content in the fruits of both cultivars are approximately at the same level (A. kolomikta > A. polygama on 1.16%). The positive correlation between antioxidant activity and the general content of polyphenols is confirmed at both cultivars. Actinidia kolomikta genotypes Chempion and Lakomka and Actinidia polygama ones Tselebnaya and Uzorchataya showed the best results. The correct individual choice of actinidia fruits that are the best ones at the biochemical composition and the content of micronutrients allows supplying the consumers with food products.

Light Microclimate-Driven Changes at Transcriptional Level in Photosynthetic Grape Berry Tissues

Viticulture practices that change the light distribution in the grapevine canopy can interfere with several physiological mechanisms, such as grape berry photosynthesis and other metabolic pathways, and consequently impact the berry biochemical composition, which is key to the final wine quality. We previously showed that the photosynthetic activity of exocarp and seed tissues from a white cultivar (Alvarinho) was in fact responsive to the light microclimate in the canopy (low and high light, LL and HL, respectively), and that these different light microclimates also led to distinct metabolite profiles, suggesting a berry tissue-specific interlink between photosynthesis and metabolism. In the present work, we analyzed the transcript levels of key genes in exocarps and seed integuments of berries from the same cultivar collected from HL and LL microclimates at three developmental stages, using real-time qPCR. In exocarp, the expression levels of genes involved in carbohydrate metabolism (VvSuSy1), phenylpropanoid (VvPAL1), stilbenoid (VvSTS1), and flavan-3-ol synthesis (VvDFR, VvLAR2, and VvANR) were highest at the green stage. In seeds, the expression of several genes associated with both phenylpropanoid (VvCHS1 and VvCHS3) and flavan-3-ol synthesis (VvDFR and VvLAR2) showed a peak at the véraison stage, whereas that of RuBisCO was maintained up to the mature stage. Overall, the HL microclimate, compared to that of LL, resulted in a higher expression of genes encoding elements associated with both photosynthesis (VvChlSyn and VvRuBisCO), carbohydrate metabolism (VvSPS1), and photoprotection (carotenoid pathways genes) in both tissues. HL also induced the expression of the VvFLS1 gene, which was translated into a higher activity of the FLS enzyme producing flavonol-type flavonoids, whereas the expression of several other flavonoid pathway genes (e.g., VvCHS3, VvSTS1, VvDFR, and VvLDOX) was reduced, suggesting a specific role of flavonols in photoprotection of berries growing in the HL microclimate. This work suggests a possible link at the transcriptional level between berry photosynthesis and pathways of primary and secondary metabolism, and provides relevant information for improving the management of the light microenvironment at canopy level of the grapes.

Sucrose Metabolism and Transport in Grapevines, with Emphasis on Berries and Leaves, and Insights Gained from a Cross-Species Comparison

In grapevines, as in other plants, sucrose and its constituents glucose and fructose are fundamentally important and carry out a multitude of roles. The aims of this review are three-fold. First, to provide a summary of the metabolism and transport of sucrose in grapevines, together with new insights and interpretations. Second, to stress the importance of considering the compartmentation of metabolism. Third, to outline the key role of acid invertase in osmoregulation associated with sucrose metabolism and transport in plants.

Non-structural Carbohydrate Metabolism in the Flesh of Stone Fruits of the Genus Prunus (Rosaceae) - A Review

Non-structural carbohydrates are abundant constituents of the ripe flesh of all stone fruits. The bulk of their content comprises sucrose, glucose, fructose and sorbitol. However, the abundance of each of these carbohydrates in the flesh differs between species, and also with its stage of development. In this article the import, subcellular compartmentation, contents, metabolism and functions of non-structural carbohydrates in the flesh of commercially cultivated stone fruits of the family Rosaceae are reviewed.

Stone Fruits: Growth and Nitrogen and Organic Acid Metabolism in the Fruits and Seeds-A Review

Stone fruits of the Rosaceae family consist of several distinct parts, and these include the flesh, woody endocarp, and seed. To understand the metabolism of these fruits, it is necessary to have knowledge of both their structure and growth characteristics. The nitrogen metabolism of the different tissues of stone fruits is interlinked. For example, there is an import and storage of nitrogenous compounds in the endocarp that are then exported to the seed. Moreover, there are links between the metabolism of nitrogen and that of malic/citric acids. In this article, the structure and growth characteristics, together with the import/export, contents, metabolism, and functions of nitrogenous compounds and organic acids in the different parts of stone fruits and their seeds are reviewed.

Proteomic analysis of pear (Pyrus pyrifolia) ripening process provides new evidence for the sugar/acid metabolism difference between core and mesocarp

Pears are one of the most popular nutrient-rich fruits in the world. The pear core and mesocarp have significantly different metabolism, although they display similar profiles. Most strikingly, the core is more acidic in taste. Our results showed that there is more titrated acid but lower total soluble solids in the core compared to the mesocarp, and the content of citric acid was more than 17-fold higher in the core compared to the mesocarp at the ripening stage. Proteomics was used to investigate the difference between core and mesocarp tissues during "Cuiguan" pear ripening. Fifty-four different protein expression patterns were identified in the core and mesocarp. In general, common variably expressed proteins between the core and mesocarp were associated with important physiological processes, such as glycolysis, pyruvate metabolic processes, and oxidative stress. Further, protein level associated qRT-PCR verification revealed a higher abundance of fructose-bisphosphate aldolase and NADP-dependent malic enzymes, which may play a role in the low acid content in the mesocarp, whereas a higher abundance of disulfide isomerase-like 2-2 and calcium-dependent lipid-binding in the core may explain why it is less prone to accumulate sugar. The different levels of a few typical ROS scavenger enzymes suggested that oxidative stress is higher in the core than in the mesocarp. This study provides the first characterization of the pear core proteome and a description of its variation compared to the mesocarp during ripening.

Combined elevated temperature and soil waterlogging stresses inhibit cell elongation by altering osmolyte composition of the developing cotton (Gossypium hirsutum L.) fiber

Soil waterlogging events and high temperature conditions occur frequently in the Yangtze River Valley, yet the effects of these co-occurring stresses on fiber elongation have received little attention. In the current study, the combined effect of elevated temperature (ET) and soil waterlogging (SW) more negatively affected final fiber length (reduced by 5.4%-11.3%) than either stress alone by altering the composition of osmotically active solutes (sucrose, malate, and K⁺), where SW had the most pronounced effect. High temperature accelerated early fiber development, but limited the duration of elongation, thereby limiting final fiber length. Treatment of ET alone altered fiber sucrose content mainly through decreased source strength and the expression of the sucrose transporter gene GhSUT-1, making sucrose availability the primary determinant of final fiber length under ET. Waterlogging stress alone decreased source strength, down-regulated GhSUT-1 expression and enhanced SuSy catalytic activity for sucrose reduction. Waterlogging treatment alone also limited fiber malate production by down-regulating GhPEPC-1 & -2. However, combined elevated temperature and waterlogging limited primary cell wall synthesis by affecting GhCESAs genes and showed a negative impact on all three major osmotic solutes through the regulation of GhSUT-1, GhPEPC-1 & -2 and GhKT-1 expression and altered SuSy activity, which functioned together to produce a shorter fiber length.

VqDUF642, a gene isolated from the Chinese grape Vitis quinquangularis, is involved in berry development and pathogen resistance

The DUF642 gene VqDUF642 , isolated from the Chinese grape species V. quinquangularis accession Danfeng-2, participates in berry development and defense responses against Erysiphe necator and Botrytis cinerea. The proteins with domains of unknown function 642 (DUF642) comprise a large protein family according to cell wall proteomic analyses in plants. However, the works about functional characterization of DUF642s in plant development and resistance to pathogens are scarce. In this study, a gene encoding a DUF642 protein was isolated from Chinese grape V. quinquangularis accession Danfeng-2, and designated as VqDUF642. Its full-length cDNA contains a 1107-bp open reading frame corresponding to a deduced 368-amino acid protein. Multiple sequence alignments and phylogenetic analysis showed that VqDUF642 is highly homologous to one of the DUF642 proteins (VvDUF642) in V. vinifera. The VqDUF642 was localized to the cell wall of tobacco epidermal cells. Accumulation of VqDUF642 protein and VqDUF642 transcript abundance increased at the later stage of grape berry development in Danfeng-2. Overexpression of VqDUF642 in transgenic tomato plants accelerated plant growth and reduced susceptibility to Botrytis cinerea. Transgenic Thompson Seedless grapevine plants overexpressing VqDUF642 exhibited enhanced resistance to Erysiphe necator and B. cinerea. Moreover, VqDUF642 overexpression affected the expression of a couple of pathogenesis-related (PR) genes in transgenic tomato and grapevine upon pathogen inoculation. Taken together, these results suggest that VqDUF642 is involved in plant development and defense against pathogenic infections.

The Unusual Acid-Accumulating Behavior during Ripening of Cherimoya (Annona cherimola Mill.) is Linked to Changes in Transcription and Enzyme Activity Related to Citric and Malic Acid Metabolism

Cherimoya (Annona cherimola Mill.) is a subtropical fruit characterized by a significant increase in organic acid levels during ripening, making it an interesting model for studying the relationship between acidity and fruit flavor. In this work, we focused on understanding the balance between the concentration of organic acids and the gene expression and activity of enzymes involved in the synthesis and degradation of these metabolites during the development and ripening of cherimoya cv. “Concha Lisa”. Our results showed an early accumulation of citric acid and other changes associated with the accumulation of transcripts encoding citrate catabolism enzymes. During ripening, a 2-fold increase in malic acid and a 6-fold increase in citric acid were detected. By comparing the contents of these compounds with gene expression and enzymatic activity levels, we determined that cytoplasmic NAD-dependent malate dehydrogenase (cyNAD-MDH) and mitochondrial citrate synthase (mCS) play important regulatory roles in the malic and citric acid biosynthetic pathways.

Fruiting Branch K(+) Level Affects Cotton Fiber Elongation Through Osmoregulation

Potassium (K) deficiency in cotton plants results in reduced fiber length. As one of the primary osmotica, K(+) contributes to an increase in cell turgor pressure during fiber elongation. Therefore, it is hypothesized that fiber length is affected by K deficiency through an osmotic pathway, so in 2012 and 2013, an experiment was conducted to test this hypothesis by imposing three potassium supply regimes (0, 125, 250 kg K ha(-1)) on a low-K-sensitive cultivar, Siza 3, and a low-K-tolerant cultivar, Simian 3. We found that fibers were longer in the later season bolls than in the earlier ones in cotton plants grown under normal growth conditions, but later season bolls showed a greater sensitivity to low-K stress, especially the low-K sensitive genotype. We also found that the maximum velocity of fibre elongation (V max) is the parameter that best reflects the change in fiber elongation under K deficiency. This parameter mostly depends on cell turgor, so the content of the osmotically active solutes was analyzed accordingly. Statistical analysis showed that K(+) was the major osmotic factor affecting fiber length, and malate was likely facilitating K(+) accumulation into fibers, which enabled the low-K-tolerant genotype to cope with low-K stress. Moreover, the low-K-tolerant genotype tended to have greater K(+) absorptive capacities in the upper fruiting branches. Based on our findings, we suggest a fertilization scheme for Gossypium hirsutum that adds extra potash fertilizer or distributes it during the development of late season bolls to mitigate K deficiency in the second half of the growth season and to enhance fiber length in late season bolls.

Evidences for Chlorogenic Acid--A Major Endogenous Polyphenol Involved in Regulation of Ripening and Senescence of Apple Fruit

To learn how the endogenous polyphenols may play a role in fruit ripening and senescence, apple pulp discs were used as a model to study the influences of chlorogenic acid (CHA, a major polyphenol in apple pulp) on fruit ripening and senescence. Apple ('Golden Delicious') pulp discs prepared from pre-climacteric fruit were treated with 50 mg L(-1) CHA and incubated in flasks with 10 mM MES buffer (pH 6.0, 11% sorbitol). Compared to the control samples, treatment with CHA significantly reduced ethylene production and respiration rate, and enhanced levels of firmness and soluble solids content of the pulp discs during incubation at 25°C. These results suggested that CHA could retard senescence of the apple pulp discs. Proteomics analysis with sodium dodecyl sulfate-polyacrylamide gel electrophoresis and mass spectrometry (MALDI-TOF/TOF) revealed that the expressions of several key proteins correlated to fruit ripening and senescence were affected by the treatment with CHA. Further study showed that treating the pulp discs with CHA remarkably reduced levels of lipoxygenase, β-galactosidase, NADP-malic enzyme, and enzymatic activities of lipoxygenase and UDP-glucose pyrophosphorylase, all of which are known as promoters of fruit ripening and senescence. These results could provide new insights into the functions of endogenous phenolic compounds in fruit ripening and senescence.

Phosphoenolpyruvate carboxykinase and gluconeogenesis in grape pericarp

Glycolysis from sugars is necessary at all stages of development of grape pericarp, and this raises the question as to why gluconeogenesis from malate occurs. Phosphoenolpyruvate carboxykinase (PEPCK) is required for gluconeogenesis in grape pericarp. In this study we determined the abundance of PEPCK protein and activity in different parts of grape pericarp during its development. Both PEPCK protein and activity were present throughout development, however, in both the skin and the flesh their abundance increased greatly at the start of ripening. This coincided with the onset of the decrease in the malate content of the berry. The location of PEPCK in the pericarp at different stages of development was determined using both immunohistochemistry and dissection. We provide a possible explanation for the occurrence of gluconeogenesis in grape pericarp.

Is stored malate the quantitatively most important substrate utilised by respiration and ethanolic fermentation in grape berry pericarp during ripening?

A widely held view is that in grape pericarp glycolysis is inhibited during ripening, and that stored malate rather than sugars become the major substrate for respiration. In this study we determined what contribution stored malate could make to the substrate requirements of respiration and ethanolic fermentation in the pericarp of Cabernet Sauvignon berries during ripening. At a number of time points through development the amount of malate in the pericarp was measured. The change in malate content between each time point was then calculated, having first allowed for dilution arising from expansion of the fruit. The amount of CO2 that was released by the berry in the interval between each pair of time points was measured. It was found that the contribution that stored malate could make to the substrate requirements of respiration and ethanolic fermentation of grape pericarp was dependent on the stage of ripening. At the beginning of ripening stored malate could provide a greater proportion of substrate than later in ripening, and during the latter its contribution was relatively low. Therefore, stored malate was not the quantitatively most important substrate utilised by respiration and ethanolic fermentation in the pericarp of grape berries during most of ripening. It is likely that sugars provide the bulk of the deficit in substrate. Further, the increase in the respiratory quotient during most of ripening does not arise from the use of malate as main respiratory substrate.

Is transcriptomic regulation of berry development more important at night than during the day?

Diurnal changes in gene expression occur in all living organisms and have been studied on model plants such as Arabidopsis thaliana. To our knowledge the impact of the nycthemeral cycle on the genetic program of fleshly fruit development has been hitherto overlooked. In order to circumvent environmental changes throughout fruit development, young and ripening berries were sampled simultaneously on continuously flowering microvines acclimated to controlled circadian light and temperature changes. Gene expression profiles along fruit development were monitored during both day and night with whole genome microarrays (Nimblegen® vitis 12x), yielding a total number of 9273 developmentally modulated probesets. All day-detected transcripts were modulated at night, whereas 1843 genes were night-specific. Very similar developmental patterns of gene expression were observed using independent hierarchical clustering of day and night data, whereas functional categories of allocated transcripts varied according to time of day. Many transcripts within pathways, known to be up-regulated during ripening, in particular those linked to secondary metabolism exhibited a clearer developmental regulation at night than during the day. Functional enrichment analysis also indicated that diurnally modulated genes considerably varied during fruit development, with a shift from cellular organization and photosynthesis in green berries to secondary metabolism and stress-related genes in ripening berries. These results reveal critical changes in gene expression during night development that differ from daytime development, which have not been observed in other transcriptomic studies on fruit development thus far.

Fumarate and cytosolic pH as modulators of the synthesis or consumption of C(4) organic acids through NADP-malic enzyme in Arabidopsis thaliana

Arabidopsis thaliana is a plant species that accumulates high levels of organic acids and uses them as carbon, energy and reducing power sources. Among the enzymes that metabolize these compounds, one of the most important ones is malic enzyme (ME). A. thaliana contains four malic enzymes (NADP-ME 1-4) to catalyze the reversible oxidative decarboxylation of malate in the presence of NADP. NADP-ME2 is the only one located in the cell cytosol of all Arabidopsis organs providing most of the total NADP-ME activity. In the present work, the regulation of this key enzyme by fumarate was investigated by kinetic assays, structural analysis and a site-directed mutagenesis approach. The final effect of this metabolite on NADP-ME2 forward activity not only depends on fumarate and substrate concentrations but also on the pH of the reaction medium. Fumarate produced an increase in NADP-ME2 activity by binding to an allosteric site. However at higher concentrations, fumarate caused a competitive inhibition, excluding the substrate malate from binding to the active site. The characterization of ME2-R115A mutant, which is not activated by fumarate, confirms this hypothesis. In addition, the reverse reaction (reductive carboxylation of pyruvate) is also modulated by fumarate, but in a different way. The results indicate pH-dependence of the fumarate modulation with opposite behavior on the two activities analyzed. Thereby, the coordinated action of fumarate over the direct and reverse reactions would allow a precise and specific modulation of the metabolic flux through this enzyme, leading to the synthesis or degradation of C(4) compounds under certain conditions. Thus, the physiological context might be exerting an accurate control of ME activity in planta, through changes in metabolite and substrate concentrations and cytosolic pH.

Development and metabolism of the fruit and seed of the Japanese plum Ozark premier (Rosaceae)

The growth characteristics of some plums and their component parts have been previously studied, as have some aspects of their developmental anatomy and composition. However, little is known about either their metabolism or about the interactions between the metabolism of their component parts. In this study we investigated these aspects in the Japanese plum Ozark Premier. Throughout fruit and seed development, changes in sugar and organic acid contents, protein composition and abundance of selected enzymes were determined. In the stone, there was a transient accumulation of vegetative storage proteins. These were subsequently mobilized and this coincided with the onset of the lignification of the stone and the start of storage protein accumulation in the seed. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) was present in the seeds, even though they lacked chlorophyll, and its presence may be related to limited gas exchange. In the flesh of some fruits, phosphoenolpyruvate carboxykinase (PEPCK) and NADP malic enzyme (NADP-ME) are thought to function in the dissimilation of malate and/or citrate during ripening. However, PEPCK and NADP-ME were present in plum flesh for most of its development, although there was no net dissimilation of malate until the latter stages of ripening. There is an interaction between the developing seed and endocarp with respect to the utilization of imported sugars and amino acids. An hypothesis is presented to account for the presence of PEPCK and NADP-ME enzyme in plum flesh when there was no net dissimilation of organic acids.

Expression and manipulation of phosphoenolpyruvate carboxykinase 1 identifies a role for malate metabolism in stomatal closure

Malate, along with potassium and chloride ions, is an important solute for maintaining turgor pressure during stomatal opening. Although malate is exported from guard cells during stomatal closure, there is controversy as to whether malate is also metabolised. We provide evidence that phosphoenolpyruvate carboxykinase (PEPCK), an enzyme involved in malate metabolism and gluconeogenesis, is necessary for full stomatal closure in the dark. Analysis of the Arabidopsis PCK1 gene promoter indicated that this PEPCK isoform is specifically expressed in guard cells and trichomes of the leaf. Spatially distinct promoter elements were found to be required for post-germinative, vascular expression and guard cell/trichome expression of PCK1. We show that pck1 mutant plants have reduced drought tolerance, and show increased stomatal conductance and wider stomatal apertures compared with the wild type. During light-dark transients the PEPCK mutant plants show both increased overall stomatal conductance and less responsiveness of the stomata to darkness than the wild type, indicating that stomata get 'jammed' in the open position. These results show that malate metabolism is important during dark-induced stomatal closure and that PEPCK is involved in this process.

Increasing the source/sink ratio in Vitis vinifera (cv Sangiovese) induces extensive transcriptome reprogramming and modifies berry ripening

BACKGROUND

Cluster thinning is an agronomic practice in which a proportion of berry clusters are removed from the vine to increase the source/sink ratio and improve the quality of the remaining berries. Until now no transcriptomic data have been reported describing the mechanisms that underlie the agronomic and biochemical effects of thinning.

RESULTS

We profiled the transcriptome of Vitis vinifera cv. Sangiovese berries before and after thinning at veraison using a genome-wide microarray representing all grapevine genes listed in the latest V1 gene prediction. Thinning increased the source/sink ratio from 0.6 to 1.2 m2 leaf area per kg of berries and boosted the sugar and anthocyanin content at harvest. Extensive transcriptome remodeling was observed in thinned vines 2 weeks after thinning and at ripening. This included the enhanced modulation of genes that are normally regulated during berry development and the induction of a large set of genes that are not usually expressed.

CONCLUSION

Cluster thinning has a profound effect on several important cellular processes and metabolic pathways including carbohydrate metabolism and the synthesis and transport of secondary products. The integrated agronomic, biochemical and transcriptomic data revealed that the positive impact of cluster thinning on final berry composition reflects a much more complex outcome than simply enhancing the normal ripening process.

Phosphoenolpyruvate carboxykinase in cherry (Prunus avium L.) fruit during development

In this study the abundance and location of phosphoenolpyruvate carboxykinase (PEPCK) was determined in the flesh and skin of the sweet cherry (Prunus avium L.) cultivar Durone Nero II during development. PEPCK was not present in young fruit but appeared in both tissues as the fruit increased in size. In these there was no net dissimilation of malic acid, which accounts for the bulk of their organic acid contents when PEPCK was present. To assist in understanding the function of PEPCK, the abundance of a number of other enzymes was determined. These enzymes were aspartate aminotransferase (AspAT), glutamine synthetase (GS), phosphoenolpyruvate carboxylase (PEPC), pyruvate, orthophosphate dikinase (PPDK), and ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco). A potential role for PEPCK in the regulation of pH and the utilization of malate in gluconeogenesis in the flesh and skin of cherries is presented.

Metabolism of the seed and endocarp of cherry (Prunus avium L.) during development

In this study some aspects of organic and amino acid metabolism in cherry endocarp and seed were investigated during their development. The abundance and location of a number of enzymes involved in these processes were investigated. These enzymes were aspartate aminotransferase (AspAT; EC:2.6.1.1), glutamine synthetase (GS; EC:6.3.1.2), phosphoenolpyruvate carboxylase (PEPC; EC:4.1.1.31), phosphoenolpyruvate carboxykinase (PEPCK; EC:4.1.1.49), and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC:4.1.1.39). There was a transient and massive accumulation of vegetative storage proteins in the endocarp. These proteins were remobilised as the endocarp lignified and at the same time that proteins were accumulated in the seed. This raised the possibility that a proportion of imported amino acids were temporarily stored in the endocarp as protein, and that these were later utilised by the seed when it started to accumulate storage proteins. Rubisco was present in the embryo and integuments of the seed although no chlorophyll was present. This is the first time that Rubisco has been detected in non-green seeds. The maximum abundance of Rubisco in the seed coincided with the deposition of seed storage proteins. A possible function for Rubisco in cherry seed is discussed. PEPCK was located in the integuments and appeared when seed storage proteins were being accumulated. In the integuments and embryo AspAT, GS, PEPC and Rubisco also appeared, or greatly increased in abundance, when seed storage proteins were being deposited.

Expression and tissue and subcellular localization of anthocyanidin synthase (ANS) in grapevine

Anthocyanidin synthase (ANS) is one of the key enzymes in the biosynthesis of both anthocyanins and proanthocyanidins in grapevine. Although substantial researches have investigated ANS gene expression and regulation at the transcriptional level, little is yet known about protein expression and distribution in grapevine. Here, the expression and tissue and subcellular localization of ANS in different Cabernet sauvignon grapevine tissues were investigated by using the techniques of Western blotting, immunohistochemical localization, immuno-electron microscopy, and confocal microscopy. The results showed that the ANS was expressed in the grape berries, leaves, stems, petioles, and leaf buds. In grape berry skin and flesh, ANS expression is developmental dependent. Immunohistochemical analysis revealed that ANS is primarily distributed in the exocarp, mesocarp, and seed of the fruit; in palisade and spongy tissues of the leaves; in the primary phloem and pith ray in the stems; and in the growth point and leaf primordium of the leaf buds. Furthermore, at the subcellular level, the ANS was mainly localized in the cytoplasm regardless of cell types and some ANS were also found in the nucleus in the mesocarp vascular bundle and leaf bud cells. This research will give further insight for the biosynthesis and regulation of different flavonoid compounds in grapevine.

Microarray analysis of ripening-regulated gene expression and its modulation by 1-MCP and hexanal

Hexanal, an inhibitor of phospholipase D, has been successfully applied for the pre- and post-harvest treatment of fruits, vegetables and flowers. Changes in gene expression induced by hexanal and the ethylene antagonist 1-MCP, were analyzed by microarray using TOM2 tomato oligo-array containing approximately 12 000 unigenes. Mature green tomato fruits were treated with 1-MCP and hexanal, RNA isolated after 10 days of storage, and labeled cDNA synthesized for microarray analysis. A large variation in gene expression profile was observed in 1-MCP-treated fruits. Genes for ethylene biosynthetic pathway enzymes such as ACC- synthase/oxidase, ethylene receptor and ethylene response factors were heavily down-regulated in 1-MCP-treated fruits. In addition, genes for key enzymes involved in cell wall degradation and carotenoid development pathways were down-regulated. Hexanal treatment significantly down-regulated ACC-synthase, and to a lesser extent, other components of ethylene signal transduction. By contrast to MCP-treated fruits, hexanal-treated fruits gradually ripened and showed higher levels of lycopene and β-carotene. GC-MS analysis of volatiles showed a higher level of major volatile components in hexanal-treated fruits. Similarities in the modulation of gene expression by hexanal and 1-MCP suggest that hexanal, in addition to being a PLD inhibitor, may also act as a weak ethylene inhibitor.

Proteins involved in biotic and abiotic stress responses as the most significant biomarkers in the ripening of Pinot Noir skins

We propose an integrated approach, obtained by the combination of multivariate statistics and proteomics, useful to isolate candidate biomarkers for the evaluation of grape ripening. We carried out a comparative 2-DE analysis of grape skins collected in three moments of ripening and analyzed the spot volume dataset through the application of principal component analysis followed by forward stepwise-linear discriminant analysis. This technique allowed to discriminate véraison, quite mature and mature samples, and to sort the matched spots according to their significance. We identified 36 spots showing high discriminating coefficients through liquid chromatography - electrospray ionization - tandem mass spectrometry (LC-ESI-MS/MS). Most of them were involved in biotic and abiotic stress responses indicating these enzymes as good candidate markers of berry ripening. These evidences hint at a likely developmental role of these proteins, in addition to their reported activity in stress events. Restricting the same statistical analysis to the samples belonging to the two last stages, it was indicated that this approach can clearly distinguish these close and similar phases of berry development. Taken all together, these results bear out that the employment of the combination of 2-DE and multivariate statistics is a reliable tool in the identification of new protein markers for describing the ripening phases and to assess the overall quality of the fruit.

Proteomic analysis of the effects of ABA treatments on ripening Vitis vinifera berries

The control of ripening of the non-climacteric grapevine fruit is still a matter of debate, but several lines of evidence point to an important role for the hormone abscisic acid (ABA). The effects of ABA treatments on Cabernet Sauvignon berries before and at véraison were studied using a 2-DE proteomic approach. Proteins from whole deseeded berries (before véraison) and berry flesh and skin (at véraison) treated with 0.76 mM ABA and collected 24 h after treatment were separated and analysed. A total of 60 protein spots showed significant variations between treated and control berries, and 40 proteins, mainly related to general metabolism and cell defence, were identified by LC MS/MS. Our results show that ABA acts mainly through the regulation of mostly the same proteins which are involved in the ripening process, and that several of these changes share common elements with the ABA-induced responses in vegetative tissues.

Distribution of resveratrol and stilbene synthase in young grape plants (Vitis vinifera L. cv. Cabernet Sauvignon) and the effect of UV-C on its accumulation

Current research indicated that the resveratrol was mainly accumulated in the skin of grape berry, however, little is yet known about the distribution of resveratrol, as well as the regulation mechanism at protein level and the localization of stilbene synthase (malonyl-CoA:4-coumaroyl-CoA malonyltransferase; EC 2.3.1.95; STS), a key enzyme of resveratrol biosynthesis, in young grape plants (Vitis vinifera L. cv. Cabernet Sauvignon). Resveratrol, whose constitutive level ranged from 0.2 mg kg(-1) FW to 16.5 mg kg(-1) FW, could be detected in stem, axillary bud, shoot tip, petiole, root and leaf of grape plants. Among them, stem phloems presented the most abundant of resveratrol, and the leaves presented the lowest. Interestingly, the level of STS mRNA and protein were highest in grape leaves. And the analysis of immunohistochemical showed the tissue-specific distribution of STS in different organs, presenting the similar results compared with the amount of protein. And the subcellular localization revealed that the cell wall in different tissues processed the most golden particles representing STS. Subjecting to UV-C irradiation, resveratrol and STS were both intensely stimulated in grape leaves, with the similar response pattern. Results above indicated that distribution of resveratrol and STS in grape was organ-specific and tissue-specific. And the accumulation of resveratrol induced by UV-C was regulated by transcriptional and translational level of STS.

Regulation of malate metabolism in grape berry and other developing fruits

Organic acids are present in all plants, supporting numerous and varied facets of cellular metabolism. The type of organic acid found, and the levels to which they accumulate are extremely variable between species, developmental stages and tissue types. Acidity plays important roles in the organoleptic properties of plant tissues, where examples of both enhanced and reduced palatability can be ascribed to the presence of specific organic acids. In fruits, sourness is generally attributed to proton release from acids such as citric, malic, oxalic, quinic, succinic and tartaric, while the anion forms each contribute a distinct taste. Acidity imposes a strong influence on crop quality, and is an important factor in deciding the harvest date, particularly for fruits where acidity is important for further processing, as in wine grapes. In the grape, as for many other fruits, malate is one of the most prevalent acids, and is an important participant in numerous cellular functions. The accumulation of malate is thought to be due in large part to de novo synthesis in fruits such as the grape, through metabolism of assimilates translocated from leaf tissues, as well as photosynthetic activity within the fruit itself. During ripening, the processes through which malate is catabolised are of interest for advancing metabolic understanding, as well as for potential crop enhancement through agricultural or molecular practices. A body of literature describes research that has begun to unravel the regulatory mechanisms of enzymes involved in malate metabolism during fruit development, through exploration of protein and gene transcript levels. Datasets derived from a series of recent microarray experiments comparing transcript levels at several stages of grape berry development have been revisited, and are presented here with a focus on transcripts associated with malate metabolism. Developmental transcript patterns for enzymes potentially involved in grape malate metabolism have shown that some flux may occur through pathways that are less commonly regarded in ripening fruit, such as aerobic ethanol production. The data also suggest pyruvate as an important intermediate during malate catabolism in fruit. This review will combine an analysis of microarray data with information available on protein and enzyme activity patterns in grapes and other fruits, to explore pathways through which malate is conditionally metabolised, and how these may be controlled in response to developmental and climatic changes. Currently, an insufficient understanding of the complex pathways through which malate is degraded, and how these are regulated, prevents targeted genetic manipulation aimed at modifying fruit malate metabolism in response to environmental conditions.

Involvement of phospholipase D in the low temperature acclimation-induced thermotolerance in grape berry

Both phospholipase D (PLD, EC 3.1.4.4) and salicylic acid (SA) play important roles in response to external stimulation and activating defense system in plants. However, roles of the two signals in plants during the development of thermotolerance induced by low temperature acclimation remain unclear. In the experiment presented in the paper, grape berries (Vitis vinifera L. cv. Chardonnay) were pretreated at 8 degrees C for 3h and then transferred to 45 degrees C for heat stress. Compared with the control without low temperature pretreatment, membrane permeability and malondialdehyde (MDA) contents were reduced and the expression of HSP73 increased in the low temperature-pretreated berries under heat stress. During low temperature acclimation, PLD, SA and HSP73 could be activated. Meanwhile, the expression of HSP73 and the accumulation of free SA induced by low temperature can be inhibited by PLD activity inhibitor. All these results suggest that the activation of PLD is an early response to low temperature, and it is involved in the accumulation of free SA and the development of thermotolerance induced by low temperature acclimation.

Cloning, identification, expression analysis and phylogenetic relevance of two NADP-dependent malic enzyme genes from hexaploid wheat

The NADP-dependent malic enzyme (NADP-ME; EC1.1.1.40) found in many metabolic pathways catalyzes the oxidative decarboxylation of L-malate, producing pyruvate, CO(2) and NADPH. The NADP-MEs have been well studied in C4 plants but not well in C3 plants. In this study, we identified the NADP-ME isoforms from hexaploid wheat (Triticum aestivum L). Two different NADP-ME transcripts were first identified in this C3 plant. The first is named TaNADP-ME1 [NCBI: EU170134] and encodes a putative plastidic isoform, while the second is named TaNADP-ME2 [NCBI: EU082065] and encodes a cytosolic counterpart. Sequence alignment shows that the two NADP-ME isoforms share an identity of 73.26% in whole amino acids and 64.08% in nucleotide sequences. The phylogenetic analysis deciphers the two NADP-MEs as belonging to the monocots (Group II), which closely resemble OschlME6 and OscytME2, respectively. Tissue-specific analyses indicate that the two NADP-ME genes are both expressed in root, stem and leaf, and that TaNADP-ME1 is a leaf-abundant isoform. Semi-quantitative RT-PCR analysis show that the two NADP-ME transcripts in wheat leaves respond differently to low temperature, salt, dark and drought stresses stimuli and to exogenous abscisic acid (ABA) and salicylic acid (SA). Our results demonstrate that exogenous hormones (ABA and SA), as well as salt, low temperature, dark and drought stresses can regulate the expressions of TaNADP-ME1 and TaNADP-ME2 in wheat. This indicates that the two NADP-ME genes may play an important role in the response of wheat to ABA, SA, low temperature, salt, dark and drought stress.

Prokaryotic expression, polyclonal antibody preparation of the stilbene synthase gene from grape berry and its different expression in fruit development and under heat acclimation

Stilbene synthase (STS, EC 2.3.1.95) leads to the production of resveratrol compounds, which are major components of the phytoalexin response against fungal pathogens of the plant and are highly bioactive substances of pharmaceutical interest. STS expression and regulation are important. Temperature is one of the main external factors affecting phytoalexin accumulation in plant tissues, the effect of temperature on resveratrol synthesis and stilbene synthase expression in grape berries has not been reported before. Here we cloned the full-length sts cDNA with 1179bp from grape berry via PCR, and then introduced into an expressed plasmid pET-30a(+) vector at the EcoRI and XhoI restriction sites. With the isopropyl-beta-d-thiogalactoside (IPTG) induced, the pET-sts was highly expressed in Escherichia coli BL21 (DE3) pLysS cells. A fusion protein with the His-Tag was purified by Ni-NTA His.Bind Resin and then used as the antigen to immunize a New Zealand rabbit. Furthermore, the antiserum was precipitated by 50% saturated ammonium sulfate and DEAE-Sephadex A-50 chromatography to obtain the immunoglobulin G (IgG) fraction. These results provide a substantial basis for the further studies of the STS in grape berry as well as in other species of plants. The sts expression in fruit development and in response to heat acclimation was then assayed. The results indicated STS was regulated in fruits depending on the developmental stage and significantly accumulation of STS mRNA and synthesis of new STS protein during the early of heat acclimation, this work offers an important basis for further investigating the mechanism of post-harvest fruit adaptation to environmental stresses.

Analysis of grape berry cell wall proteome: a comparative evaluation of extraction methods

Different methods were tested for the extraction of proteins from the cell wall-enriched fraction (CWEf) obtained from a sample formed by skin and seeds of ripe berries of Vitis vinifera L. cv. Cabernet Sauvignon. The CWEf was isolated using a disruptive approach that involves tissue homogenization and precipitation by centrifugation. To extract proteins, the CWEf was treated with CaCl(2) and LiCl in two successive steps or, alternatively, with phenol. The efficiency of the protocols was evaluated by measuring protein yield and by analyzing two-dimensional gel electrophoresis (2-DE) gels for the highest detectable spot number and the greatest spot resolution. The phenol method was also adopted for the extraction of proteins from the cytosolic fraction (CYf). The comparison of 2-DE reference maps of protein extracts from CWEf and CYf indicated the presence of both common traits and unique characteristics. To survey this aspect some spots detected in both fractions or present in only one fraction were analyzed by liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Of the 47 spots identified, some were found to be cell wall proteins, while others were proteins not traditionally considered as localized in the apoplastic space. The data presented here provide initial information regarding the apoplastic proteome of grape berry tissues, but also raise the issue of the technical problems that characterize the isolation of cell wall proteins from these very hardy tissues.

Proteome changes in the skin of the grape cultivar Barbera among different stages of ripening

Background

Grape ripening represents the third phase of the double sigmoidal curve of berry development and is characterized by deep changes in the organoleptic characteristics. In this process, the skin plays a central role in the synthesis of many compounds of interest (e.g. anthocyanins and aroma volatiles) and represents a fundamental protective barrier against damage by physical injuries and pathogen attacks. In order to improve the knowledge on the role of this tissue during ripening, changes in the protein expression in the skin of the red cultivar Barbera at five different stages from véraison to full maturation were studied by performing a comparative 2-DE analysis.

Results

The proteomic analysis revealed that 80 spots were differentially expressed throughout berry ripening. Applying a two-way hierarchical clustering analysis to these variations, a clear difference between the first two samplings (up to 14 days after véraison) and the following three (from 28 to 49 days after véraison) emerged, thus suggesting that the most relevant changes in protein expression occurred in the first weeks of ripening. By means of LC-ESI-MS/MS analysis, 69 proteins were characterized. Many of these variations were related to proteins involved in responses to stress (38%), glycolysis and gluconeogenesis (13%), C-compounds and carbohydrate metabolism (13%) and amino acid metabolism (10%).

Conclusion

These results give new insights to the skin proteome evolution during ripening, thus underlining some interesting traits of this tissue. In this view, we observed the ripening-related induction of many enzymes involved in primary metabolism, including those of the last five steps of the glycolytic pathway, which had been described as down-regulated in previous studies performed on whole fruit. Moreover, these data emphasize the relevance of this tissue as a physical barrier exerting an important part in berry protection. In fact, the level of many proteins involved in (a)biotic stress responses remarkably changed through the five stages taken into consideration, thus suggesting that their expression may be developmentally regulated.

Cloning of phospholipase D from grape berry and its expression under heat acclimation

To investigate whether phospholipase D (PLD, EC 3.1.4.4) plays a role in adaptive response of post-harvest fruit to environment, a PLD gene was firstly cloned from grape berry (Vitis Vinifera L. cv. Chardonnay) using RT-PCR and 3'- and 5'-RACE. The deduced amino acid sequence (809 residues) showed 84.7% identity with that of PLD from Ricinus communis. The secondary structures of this protein showed the characteristic C2 domain and two active sites of a phospholipid-metabolizing enzyme. The PLD activity and its expression in response to heat acclimation were then assayed. The results indicated PLD was significantly activated at enzyme activity, as well as accumulation of PLD mRNA and synthesis of new PLD protein during the early of heat acclimation, primary suggesting that the grape berry PLD may be involved in the heat response in post-harvest grape berry. This work offers an important basis for further investigating the mechanism of post-harvest fruit adaptation to environmental stresses.

Tissue-specific mRNA expression profiling in grape berry tissues

Background

Berries of grape (Vitis vinifera) contain three major tissue types (skin, pulp and seed) all of which contribute to the aroma, color, and flavor characters of wine. The pericarp, which is composed of the exocarp (skin) and mesocarp (pulp), not only functions to protect and feed the developing seed, but also to assist in the dispersal of the mature seed by avian and mammalian vectors. The skin provides volatile and nonvolatile aroma and color compounds, the pulp contributes organic acids and sugars, and the seeds provide condensed tannins, all of which are important to the formation of organoleptic characteristics of wine. In order to understand the transcriptional network responsible for controlling tissue-specific mRNA expression patterns, mRNA expression profiling was conducted on each tissue of mature berries of V. vinifera Cabernet Sauvignon using the Affymetrix GeneChip^® Vitis oligonucleotide microarray ver. 1.0. In order to monitor the influence of water-deficit stress on tissue-specific expression patterns, mRNA expression profiles were also compared from mature berries harvested from vines subjected to well-watered or water-deficit conditions.

Results

Overall, berry tissues were found to express approximately 76% of genes represented on the Vitis microarray. Approximately 60% of these genes exhibited significant differential expression in one or more of the three major tissue types with more than 28% of genes showing pronounced (2-fold or greater) differences in mRNA expression. The largest difference in tissue-specific expression was observed between the seed and pulp/skin. Exocarp tissue, which is involved in pathogen defense and pigment production, showed higher mRNA abundance relative to other berry tissues for genes involved with flavonoid biosynthesis, pathogen resistance, and cell wall modification. Mesocarp tissue, which is considered a nutritive tissue, exhibited a higher mRNA abundance of genes involved in cell wall function and transport processes. Seeds, which supply essential resources for embryo development, showed higher mRNA abundance of genes encoding phenylpropanoid biosynthetic enzymes, seed storage proteins, and late embryogenesis abundant proteins. Water-deficit stress affected the mRNA abundance of 13% of the genes with differential expression patterns occurring mainly in the pulp and skin. In pulp and seed tissues transcript abundance in most functional categories declined in water-deficit stressed vines relative to well-watered vines with transcripts for storage proteins and novel (no-hit) functional assignments being over represented. In the skin of berries from water-deficit stressed vines, however, transcripts from several functional categories including general phenypropanoid and ethylene metabolism, pathogenesis-related responses, energy, and interaction with the environment were significantly over-represented.

Conclusion

These results revealed novel insights into the tissue-specific expression mRNA expression patterns of an extensive repertoire of genes expressed in berry tissues. This work also establishes an extensive catalogue of gene expression patterns for future investigations aimed at the dissection of the transcriptional regulatory hierarchies that govern tissue-specific expression patterns associated with tissue differentiation within berries. These results also confirmed that water-deficit stress has a profound effect on mRNA expression patterns particularly associated with the biosynthesis of aroma and color metabolites within skin and pulp tissues that ultimately impact wine quality.

Sequence analysis and transcriptional profiling of two vacuolar H+ -pyrophosphatase isoforms in Vitis vinifera

Gene expression of grapevine vacuolar H(+)-pyrophosphatase (V-PPase EC 3.6.1.1.) during fruit ripening has previously been reported. Here we report on putative multiple V-PPase isoforms in grapevine. In this study a full-length cDNA sequence with an open reading frame of 2,295 nucleotides encoding a V-PPase gene (vpp2: acc. nr. AJ557256) was cloned. Sequence analyses of the deduced amino acid residues and RT-PCR experiments indicated that Vitis vinifera L. has at least two distinct isoforms of the V-PPase gene. Bioinformatic analyses of 13 V-PPase protein sequences revealed two highly conserved motifs associated with pyrophosphate (PPi) binding and response to stress, respectively. Both V-PPase isoforms were expressed at higher levels in the late post-véraison stage of grape berry ripening. Results also showed that the expression of grapevine V-PPase was induced by cold stress.

Changes and subcellular localizations of the enzymes involved in phenylpropanoid metabolism during grape berry development

The phenylpropanoid pathway yields a variety of phenolics that are closely associated with fruit qualities in addition to structural and defense-related functions. However, very little has been reported concerning its metabolism in fruit. This experiment was designed to assess changes of eleven phenolic acids in grape berry (Vitis vinifera L. cv. Cabernet Sauvignon) and explore both the activities and amounts of three key enzymes--phenylalanine ammonia-lyase (PAL), cinnamate-4-hydroxylase (C4H) and 4-coumarate:coenzyme A ligase (4CL)--catalyzing the biosynthesis of these compounds during berry development. Finally, the subcellular localizations of the enzymes within berry tissues were also investigated using immuno-gold electron microscopic technique. The results indicated that the contents of gallic, protocatechuic, gentisic and caffeic acid all changed drastically during berry development, while other compounds containing p-hydroxybenzoic, vanillic, syringic, chlorogenic, p-coumaric, ferulic and sinapic acid varied only slightly. Activities of PAL, C4H and 4CL showed similar pattern changes with two accumulated peaks throughout berry development. In addition, their activities all showed a highly positive correlation with the total contents of phenolic acids, whereas the immunoblotting analysis showed that changes in enzyme activities were independent of the enzyme amounts. Results from the subcellular-localization study revealed that PAL was mainly present in the cell walls, secondarily thickened walls, and the parenchyma cells of the berry mesocarp cells, C4H was found primarily in the chloroplast (plastid) and nucleus and 4CL predominantly in the secondarily thickened walls and the parenchyma cells of mesocarp vascular tissue.

The grapevine fleshless berry mutation. A unique genotype to investigate differences between fleshy and nonfleshy fruit

In flowering plants, fruit morphogenesis is a distinct process following fertilization resulting in the formation of a specialized organ associated with seeds. Despite large variations in types and shapes among species, fleshy fruits share common characteristics to promote seed dispersal by animals such as organ growth and metabolite accumulation to attract animal feeding. The molecular biology of fruit ripening has received considerable attention, but little is known about the determinism of early fruit morphogenesis and why some fruits are fleshy while others lack flesh. We have identified in grapevine (Vitis vinifera) a mutation we have named fleshless berry (flb) that reduces by 20 times the weight of the pericarp at ripening without any effect on fertility or seed size and number. The flb mutation strongly impaired division and differentiation of the most vacuolated cells in the inner mesocarp. The timing of ripening was not altered by the mutation although the accumulation of malic acid in the green stage was noticeably reduced while sucrose content (instead of hexoses) increased during ripening. The mutation segregates as a single dominant locus. These results indicate that the Flb- mutant is suitable material to advance our understanding of the genetic and developmental processes involved in the differentiation of an ovary into a fruit.

Characterizing the grape transcriptome. Analysis of expressed sequence tags from multiple Vitis species and development of a compendium of gene expression during berry development

We report the analysis and annotation of 146,075 expressed sequence tags from Vitis species. The majority of these sequences were derived from different cultivars of Vitis vinifera, comprising an estimated 25,746 unique contig and singleton sequences that survey transcription in various tissues and developmental stages and during biotic and abiotic stress. Putatively homologous proteins were identified for over 17,752 of the transcripts, with 1,962 transcripts further subdivided into one or more Gene Ontology categories. A simple structured vocabulary, with modules for plant genotype, plant development, and stress, was developed to describe the relationship between individual expressed sequence tags and cDNA libraries; the resulting vocabulary provides query terms to facilitate data mining within the context of a relational database. As a measure of the extent to which characterized metabolic pathways were encompassed by the data set, we searched for homologs of the enzymes leading from glycolysis, through the oxidative/nonoxidative pentose phosphate pathway, and into the general phenylpropanoid pathway. Homologs were identified for 65 of these 77 enzymes, with 86% of enzymatic steps represented by paralogous genes. Differentially expressed transcripts were identified by means of a stringent believability index cutoff of > or =98.4%. Correlation analysis and two-dimensional hierarchical clustering grouped these transcripts according to similarity of expression. In the broadest analysis, 665 differentially expressed transcripts were identified across 29 cDNA libraries, representing a range of developmental and stress conditions. The groupings revealed expected associations between plant developmental stages and tissue types, with the notable exception of abiotic stress treatments. A more focused analysis of flower and berry development identified 87 differentially expressed transcripts and provides the basis for a compendium that relates gene expression and annotation to previously characterized aspects of berry development and physiology. Comparison with published results for select genes, as well as correlation analysis between independent data sets, suggests that the inferred in silico patterns of expression are likely to be an accurate representation of transcript abundance for the conditions surveyed. Thus, the combined data set reveals the in silico expression patterns for hundreds of genes in V. vinifera, the majority of which have not been previously studied within this species.

Immunolocalization of carbonic anhydrase and phosphoenolpyruvate carboxylase in developing seeds of Medicago sativa

To investigate the role of carbonic anhydrase (CA; EC 4.2.1.1) and phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) during Medicago sativa seed development, the distribution of both proteins was examined using an immunohistological approach. Both enzymes are co-localized in most ovular and embryonic tissues. In early stages of seed development, both proteins were abundant in embryo and integuments, while at subsequent stages both proteins are accumulated in endosperm, nucellus and integuments. At late stages of seed development when both endosperm and nucellus are degraded, significant accumulation of both proteins was observed in the embryo proper. Chlorophyll was found to accumulate in embryos after the heart stage and reached a maximum at mature stage. It is suggested that CA and PEPC play a role in respiratory carbon dioxide refixation while generating malate to support amino acid and/or fatty acids biosynthesis.