Background: Grafting with rootstocks is essential for the culture of many perennial fruit crops and is increasing being used in the production of annual fruits and vegetables. Our previous work based on microarrays showed that transcripts encoding enzymes of both primary and secondary metabolism were differentially expressed during graft union formation in both homo-grafts (a genotype grafted with itself) and hetero-grafts (two different genotypes grafted together). The aim of this study was to profile primary and secondary metabolites, and quantify the activity of phenylalanine ammonia lyase (PAL) and neutral invertase (NI) in the scion and rootstock tissues and the graft interface of homo and hetero-grafts of grapevine 1 month after grafting. Table-top grafting was done on over-wintering stems (canes) of grapevine and the graft interface tissues (containing some woody stem tissues and callus) were compared to the surrounding rootstock and scion tissues. The objective was to identify compounds involved in graft union formation and hetero-grafting responses. Results: A total of 54 compounds from primary and secondary metabolism (19 amino acids, five primary and 30 secondary compounds metabolites) and the activity of two enzymes were measured. The graft interface was associated with an increase in the accumulation of the branched-chain amino acids, basic amino acids, certain stilbene compounds and higher PAL and NI activity in comparison to the surrounding woody stem tissues. Some amino acids and stilbenes were identified as being accumulated differently between the graft interfaces of the scion/rootstock combinations in a manner which was unrelated to their concentrations in the surrounding woody stem tissues. Conclusions: This study revealed the modification of primary metabolism to support callus cell formation and the stimulation of stilbene synthesis at the graft interface, and how these processes are modified by hetero-grafting. Knowledge of the metabolites and/or enzymes required for successful graft union formation offer us the potential to identify markers that could be used by nurseries and researchers for selection and breeding purposes.

By analyzing the sugars extracted from oak chips toasted at various temperatures (180 to 280 °C) for various durations (10 to 30 min) in a model wine, we examined how wood polysaccharides are affected by toasting. The responses induced by toasting significantly differed among the major sugars constituting the wood. The main components of wood polysaccharides—glucose, arabinose, galactose, and xylose—were analyzed, and the results showed that galactose had the highest extraction amounts at around 220 °C of toasting, xylose at around 240 °C, and glucose at around 280 °C. On the other hand, the extraction amounts decreased with longer toasting durations. These results suggest that wood polysaccharides undergo temperature-dependent depolymerization while simultaneously undergoing denaturation. In addition, these depolymerization reactions tended to shift towards lower temperatures with longer toasting durations. The results of this study elucidate the chemical changes that occur within the wood during the toasting of oak chips and highlight the importance of the relationship between toasting temperature and duration. Additionally, this study demonstrated that by using the sugars extracted from oak chips as indicators, it is possible to partially visualize the reactions that occur within oak chips during toasting.

SUMMARY: Grafting plants uses intrinsic wound‐healing mechanisms to join together different organisms, yet the processes underpinning graft union formation remain poorly understood. To further our understanding of the molecular reprogramming triggered by grafting and wounding in a perennial plant, we characterised the transcriptome and metabolome of intact and wounded un‐grafted scions and rootstocks, and homo‐ and hetero‐grafts at 0 and 14 days after grafting/wounding in grapevine. We show that grafting triggered the coordinated activation of gene expression and the accumulation of lipids and phenolic compounds in comparison with intact tissues. We highlight an asymmetry in gene expression above and below the graft interface, which is in part not only due to carbon status, but also to intrinsic differences in gene expression between un‐grafted scions and rootstocks, and their differential responses to wounding. We found that β‐1,4‐glucanases were differentially expressed in response to both wounding and grafting and demonstrated that exogenous β‐1,4‐glucanase application increased grafting success rate. Grafting, wounding, homo‐graft and hetero‐graft‐specific transcriptome responses were characterised. The comprehensive experimental design of the dataset containing all necessary control samples allowed the identification of genes and metabolites potentially involved in wounding and grafting responses in an iconic grafted fruit crop. This is important because knowledge of genes regulating graft union formation could be leveraged for the selection of new, highly graft‐compatible cultivars in the future.