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Self-incompatibility (SI) in almond [Prunus dulcis (Miller) D.A. Webb] is of the gametophytic-type and is controlled by the S-locus, which is highly polymorphic and includes two tightly-linked genes expressed in the pistil (as an S-RNase) and in the pollen [as an S haplotype-specific F-box (SFB) protein]. Experimental evidence indicates that other proteins are also needed for the functioning of self-incompatibility. However, to date, S-RNase and SFB are the only components of the SI system identified in almond. Moreover, the cause(s) of a lack of S-RNase activity in self-compatible almonds remain(s) unclear. This work aimed to identify the other proteins involved in the self-(in)compatible response in almond by comparative quantitative analysis of the differential expression of proteins following incompatible and compatible pollinations. Four self-incompatible almond cultivars were self-pollinated or cross-pollinated, and a homozygous self-compatible almond selection was self-pollinated. Proteins were extracted from the pollinated pistils and analysed by two-dimensional difference gel electrophoresis (2D-DIGE) and high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Searches were performed against the NCBI database using the MASCOT and SEQUEST search engines and Proteome Discoverer vl.4 software. A total of 43 proteins, some with a key role in pollen-pistil interactions, were identified as being differentially expressed following incompatible or compatible pollination. These results provide the first profiles of differential protein expression during self-(in)compatibility in almond. [ABSTRACT FROM AUTHOR]

Root-to-shoot signalling via xylem sap is an important mechanism by which plants respond to stress. This signalling could be mediated by alteration in the concentrations of inorganic and/or organic molecules. The effect of salt stress on the contents of xylem sap in Brassica olarecea has been analysed by mass spectrometry in order to quantify these changes. Subcellular location of arabinogalactan proteins (AGPs) by immunogold labelling and peroxidase isozymes was also analysed by isoelectrofocusing. The xylem sap metabolome analysis demonstrated the presence of many organic compounds such as sugars, organic acids and amino acids. Of these, amino acid concentrations, particularly that of glutamine, the major amino acid in the sap, were substantially reduced by salt stress. The xylem sap proteome analysis demonstrated the accumulation of enzymes involved in xylem differentiation and lignification, such as cystein proteinases, acid peroxidases, and a putative hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyl transferase under salt stress. The peroxidase isozyme pattern showed that salt stress induced a high accumulation of an acid isoform. These results suggest that xylem differentiation and lignification is induced by salt stress. The combination of different methods to analyse the xylem sap composition provides new insights into mechanisms in plant development and signalling under salt stress. [ABSTRACT FROM AUTHOR]

Two PPO preparations, one soluble and one particulate, were monitored at eight different developmental stages after anthesis of tomato fruits. Both PPO preparations showed significant decline after the 12th day postanthesis of fruit development. Although present in every cultivar tested, the two PPO preparations varied greatly in activity among the cultivars. The addition of 1-mM synthetic hexapeptides caused inhibition over 10% on PPO activity measured in both preparations. The antibrowning effect of the β-CD Cavasol W7M on PPO activity was also evaluated. Although the two families of compounds that we describe here, hexapeptides and CDs, react in very different ways either by physically blocking the active site of PPO or, alternatively, by chelating PPO substrates, they are common antibrowning compounds that can be commercially synthesized. These inhibitors are peptides and sugars, which are not likely to cause adverse health effects. [ABSTRACT FROM AUTHOR]