Multiscale Localization of Procyanidins in Ripe and Overripe Perry Pears by Light and Transmission Electron Microscopy.

Histochemical staining with 4-dimethylaminocinnamaldehyde (DMACA), light microscopy, and transmission electron microscopy (TEM) were applied to characterize procyanidin localization at ripe and overripe stages in perry pear flesh (cv. 'De Cloche'). Pear flesh contained stone cell clusters surrounded by very large parenchyma cells. DMACA staining showed procyanidins mainly located in parenchyma cells from the fruit mesocarp. Under light microscopy and TEM, procyanidins appeared in the vacuole of parenchyma cells as uniformly stained granules, probably tannosomes. They were differently dispersed in ripe and overripe perry pears, as the granules remained free inside the vacuole in ripe pears and mostly attached to the tonoplast in overripe pears.

Pear ripeness and tissue type impact procyanidin-cell wall interactions.

Procyanidins and cell walls were extracted from pear at ripe and overripe stages in order to investigate the impact of ripening stage on their association. Procyanidin composition and structure remained stable at the overripe stage. Mid Infrared Spectroscopy (MIR) discriminated cell wall-procyanidin complex from initial purified cell wall material (CWM). Interactions between procyanidins and CWM isolated from the whole flesh (FL), parenchyma cells (PC), stone cells (ST) and skin (SK) at ripe and overripe stage were characterized using UV-Vis spectrometry using Langmuir isotherm formulation and Isothermal Titration Microcalorimetry (ITC). The affinity between procyanidins and CWM decreased as follows: PC > FL > ST > SK. The proportion of bound procyanidins increased at the overripe stage for all CWM and the maximal saturation level was obtained for overripe FL and ST. ITC indicated that associations between pear cell walls and procyanidins involved hydrogen bonds and mainly hydrophobic interactions for overripe PC.

Characterization and quantification of fruit phenolic compounds of European and Tunisian pear cultivars.

The flesh and peel of 19 pear cultivars (8 Tunisian dessert cultivars, 8 European dessert cultivars and 3 French perry pear cultivars) were studied for their phenolic composition. Phenolic compounds were identified by HPLC/ESI-MS2 and individually quantified by HPLC-DAD. Five classes of polyphenols were present: flavan-3-ols, phenolic acids, flavonols, anthocyanins and simple phenolics (hydroquinones). The total phenolic content ranged between 0.1g/kg Fresh Weight (FW) ('Conference' cultivar) and 8.6g/kg FW ('Plant De Blanc' cultivar) in the flesh and between 1.6g/kg FW ('William vert' cultivar) and 40.4g/kg FW ('Arbi Chiheb' cultivar) in the peel. Procyanidins, analyzed after thioacidolysis, were the main phenolic compounds in all pear cultivars either in the pulp or the peel, their constitutive units being essentially (-)-epicatechin. Tunisian dessert pears and French perry pears are richer in procyanidins with very high degree of polymerization (>100) for Tunisian pears. Peel procyanidins were less polymerized (from 4 to 20). Pear peel phenolic profile was more complex especially for Tunisian cultivars, with flavonols and in some cultivars anthocyanins.

Characterization of tissue specific differences in cell wall polysaccharides of ripe and overripe pear fruit.

Cell walls from flesh, parenchyma cells, stone cells and skin were isolated from ripe and overripe Pyrus communis L. cv "De Cloche" using the phenol-buffer method. Pear polysaccharides were solubilized from cell walls by sequential extractions with aqueous solutions of ammonium oxalate, Na2CO3, and increasing concentration of NaOH, to explore overripening impact. Cell walls were also differentiated using MIR spectral data. Stone cells contained high levels of xylose and lignin while parenchyma cells had high levels of glucose, uronic acids and arabinose. Sequential extractions revealed that pear pectins had highly branched rhamnogalacturonans and were extremely methylated. Xylans were the main hemicelluloseespecially for stone cells. Cellulose represented about half of all cell walls. This heterogeneous composition of pear affected differently cell wall evolutions and properties. Thus, overripening involved a decrease in arabinose and a loss of pectic side chains mostly from parenchyma cells. Changes in hemicellulose and cellulose were minor.

Differential Pigment Accumulation in Carrot Leaves and Roots during Two Growing Periods.

Carotenoids are important secondary metabolites involved in plant growth and nutritional quality of vegetable crops. These pigments are highly accumulated in carrot root, but knowledge about the impact of environmental factors on their accumulation is limited. The purpose of this work was to investigate the impact of environmental variations on carotenoid accumulation in carrot leaves and roots. In this work, carrots were grown during two contrasting periods to maximize bioclimatic differences. In leaves, carotenoid and chlorophyll contents were lower in the less favorable growing conditions, whereas relative contents were well conserved for all genotypes, suggesting a common regulatory mechanism. The down-regulation of all genes under environmental constraints demonstrates that carotenoid accumulation is regulated at the transcriptional level. In roots, the decrease in α-carotene and lutein contents was accompanied by an increase of ß-carotene relative content. At the transcriptional level, LCYB and ZEP expression increased, whereas LCYE expression decreased, in the less favorable conditions, suggesting that carotenoid biosynthesis is switched toward the ß-branch.