Integration of proteomics and metabolomics data of early and middle season Hass avocados under heat treatment.

Ripening heterogeneity of Hass avocados results in inconsistent quality fruit delivered to the triggered and ready to eat markets. This research aimed to understand the effect of a heat shock (HS) prior to controlled atmosphere (CA) storage on the reduction of ripening heterogeneity. HS prior to CA storage reduces more drastically the ripening heterogeneity in middle season fruit. Via correlation network analysis we show the different metabolomics networks between HS and CA. High throughput proteomics revealed 135 differentially expressed proteins unique to middle season fruit triggered by HS. Further integration of metabolomics and proteomics data revealed that HS reduced the glycolytic throughput and induced protein degradation to deliver energy for the alternative ripening pathways. l-isoleucine, l-valine, l-aspartic and ubiquitin carboxyl-terminal hydrolase involved in protein degradation were positively correlated to HS samples. Our study provides new insights into the effectiveness of HS in synchronizing ripening of Hass avocados.

Pre-symptomatic transcriptome changes during cold storage of chilling sensitive and resistant peach cultivars to elucidate chilling injury mechanisms.

BACKGROUND: Cold storage induces chilling injury (CI) disorders in peach fruit (woolliness/mealiness, flesh browning and reddening/bleeding) manifested when ripened at shelf life. To gain insight into the mechanisms underlying CI, we analyzed the transcriptome of 'Oded' (high tolerant) and 'Hermoza' (relatively tolerant to woolliness, but sensitive to browning and bleeding) peach cultivars at pre-symptomatic stages. The expression profiles were compared and validated with two previously analyzed pools (high and low sensitive to woolliness) from the Pop-DG population. The four fruit types cover a wide range of sensitivity to CI. The four fruit types were also investigated with the ROSMETER that provides information on the specificity of the transcriptomic response to oxidative stress. RESULTS: We identified quantitative differences in a subset of core cold responsive genes that correlated with sensitivity or tolerance to CI at harvest and during cold storage, and also subsets of genes correlating specifically with high sensitivity to woolliness and browning. Functional analysis indicated that elevated levels, at harvest and during cold storage, of genes related to antioxidant systems and the biosynthesis of metabolites with antioxidant activity correlates with tolerance. Consistent with these results, ROSMETER analysis revealed oxidative stress in 'Hermoza' and the progeny pools, but not in the cold resistant 'Oded'. By contrast, cold storage induced, in sensitivity to woolliness dependant manner, a gene expression program involving the biosynthesis of secondary cell wall and pectins. Furthermore, our results indicated that while ethylene is related to CI tolerance, differential auxin subcellular accumulation and signaling may play a role in determining chilling sensitivity/tolerance. In addition, sugar partitioning and demand during cold storage may also play a role in the tolerance/sensitive mechanism. The analysis also indicates that vesicle trafficking, membrane dynamics and cytoskeleton organization could have a role in the tolerance/sensitive mechanism. In the case of browning, our results suggest that elevated acetaldehyde related genes together with the core cold responses may increase sensitivity to browning in shelf life. CONCLUSIONS: Our data suggest that in sensitive fruit a cold response program is activated and regulated by auxin distribution and ethylene and these hormones have a role in sensitivity to CI even before fruit are cold stored.

Determination of pathogen-related enzyme action by mass spectrometry analysis of pectin breakdown products of plant cell walls.

An analytical approach using matrix-assisted laser desorption/ionization mass spectrometry for the structural characterization and assessment of the degree of polymerization of cell wall pectin-derived oligosaccharides (PDOs) in three regions of Botrytis cinerea-infected tomato fruit tissue is described. The PDOs were isolated from lesion centers (extensively macerated tissue), the area just beyond visible lesion margins, and healthy and intact tissue of an inoculated fruit, sampled at a distance from developing lesions. PDO mixtures were directly analyzed by mass spectrometry without chromatographic separation, after minimum cleanup by membrane drop dialysis. The structures identified implied the action of three different pathogen pectin-modifying enzymes. Modifications such as methyl esterification were identified by determination of exact PDO molecular masses and tandem mass spectrometry via collision-induced dissociation. We have identified four PDO series that were generated through the breakdown of homogalacturonan pectins. The decayed and lesion edge areas had fewer and less diverse PDOs than healthy tissues, possibly due to metabolic by-products of the pathogen. This analytical technique provides a simple and rapid method to characterize the pectin-derived oligosaccharides produced by in vivo digestion during pathogen infection.

Cell wall metabolism during the development of chilling injury in cold-stored peach fruit: association of mealiness with arrested disassembly of cell wall pectins.

Partially tree-ripened ripe fruit of peach (Prunus persica L.) were stored for 1-4 weeks at 5 degrees C and then ripened at 20 degrees C for 3 d to induce chilling injury. With increasing cold storage the incidence and severity of mealiness symptoms increased progressively, manifested as reduced quantities of free juice and internal flesh browning. Relative to juicy fruit, tissue of mealy fruit showed altered intercellular adhesion when examined by microscopy and, upon crushing, a higher proportion of cells remained intact and did not release cellular contents. Substantial alterations in the metabolism of cell wall polysaccharides were observed. Chelator-soluble polyuronides from mealy fruit were partially depolymerized during cold storage in a manner dissimilar to that in unripe or ripe juicy fruit, and were not depolymerized further during the ripening period. The solubility of these high molecular weight pectins remained low, and did not show the increase characteristic of juicy fruit. Furthermore, in mealy fruit the dramatic decline in the polymeric Ara content of base-soluble, matrix glycan-enriched fractions occurring during normal ripening was absent, indicating diminished disassembly of an arabinan-rich polysaccharide firmly attached to cellulose. A corresponding rise in the polymeric Ara content of the most soluble pectin fraction was also absent, as was a decline in the Gal content of this extract. The depolymerization of matrix glycans showed only minor differences between juicy and mealy fruit. After cold storage and ripening, the activities of endo-1,4-beta-glucanase (EC 3.2.1.4), endo-1,4-beta-mannanase (EC 3.2.1.78), beta-galactosidase (EC 3.2.1.23), alpha-arabinosidase (EC 3.2.1.55), and particularly endo-polygalacturonase (EC 3.2.1.15) were lower in mealy fruit than in juicy fruit, whereas pectin methylesterase activity (EC 3.1.1.11) was lower in slightly mealy and higher in very mealy fruit. The data suggest that cold storage affects the activities of numerous cell wall-modifying enzymes, with important consequences for pectin metabolism. These changes alter the properties of the primary wall and middle lamella, resulting in tissue breakage along enlarged air spaces, rather than across cells, which reduces the amount and availability of free juice upon tissue fragmentation.