• Energy Research

AbstractPhenolic compounds are secondary metabolites involved in plant innate chemical defence against pests and diseases. Their concentration varies depending on plant tissue and also on genetic and environmental factors, e.g. availability of nutrient resources. This study examines specific effects of low (LN) and high (HN) nitrogen supply on organ (root, stem and leaf) growth and accumulation of major phenolics [chlorogenic acid (CGA); rutin; kaempferol rutinoside (KR)] in nine hydroponically grown tomato cultivars. LN limited shoot growth but did not affect root growth, and increased concentrations of each individual phenolic in all organs. The strength of the response was organ‐dependent, roots being more responsive than leaves and stems. Significant differences were observed between genotypes. Nitrogen limitation did not change the phenolic content in shoots, whereas it stimulated accumulation in roots. The results show that this trade‐off between growth and defence in a LN environment can be discussed within the framework of the growth–differentiation balance hypothesis (i.e. GDBH), but highlight the need to integrate all plant organs in future modelling approaches regarding the impact of nitrogen limitation on primary and secondary metabolism.

he SUNNIVA project aims to increase the overall sustainability of vegetable processing by providing valorisation strategies to reduce waste and limiting environmental impact, while improving the nutritional properties of vegetable food products. Results obtained during the first project year indicate that; (i) The waste and by-product fractions of cabbage, tomato and black salsify have a great potential to be better utilized in the food processing chain and to serve as valuable sources for health beneficial phytochemicals (HBPC), and (ii) that tomato and grape seed press cakes have an interesting plant nutritional (NPK) profile, which makes them suitable candidates as raw material in soil amendments. Further, raw materials from tomato and cabbage, in terms of cultivars and morphological parts, has been assessed for HBPC and nutritional value as an effect of N-fertilization and processing. Experimental data for deriving numerical thermal models for agitated and static retort are obtained. Mapping of the most important underutilized vegetable biomass streams in partnering countries are under way. The development of non-destructive tools for rapid HBPC measurements in cabbage and tomato is promising, but some more calibration/validation of the method is necessary. One year into the 3-year project, we conclude that progress has been satisfactory.

Plant growth and defence are both fuelled by compounds synthesized from a common pool of carbon and nitrogen, implying the existence of a competition for carbon and nitrogen allocation to both metabolisms. The ratio of carbon to nitrogen (C:N) of an organ is often regarded as a convenient indicator of growth and quality. The purpose of this work was to assess whether or not it is possible to extend its use to characterize the trade-off between growth and defence processes. Therefore, we calculated C:N ratios in the pool of resources and in the total plant, and correlated them to the concentrations of diverse compounds of the primary and secondary metabolisms in young tomatoes. Plants were grown hydroponically at N availabilities either limiting (0.1 mM) or not (7 mM) for growth in two glasshouses maintained either under ambient or enriched (700 vpm) air CO(2). These conditions yielded a large array of C:N in fully developed leaves, developing leaves, stem and roots, sampled 27, 35 and 47 days after sowing. Growth parameters and tissue concentrations of primary metabolites (carbohydrates, starch), defence-related compounds (polyphenols, glycoalkaloids), lignin, nitrate, ammonium, C and N were analyzed. Net CO(2) exchange rate was also measured at the last sampling date. Low N limited plant growth more than photosynthesis. The C:N in the resource pool was far higher than the total C:N. Starch was the most responsive compound, attaining high concentration under high C:N, whereas lignin remained stable. Chlorogenic acid, rutin, kaempferol-rutinoside and tomatine concentrations correlated positively to C:N. The same patterns were observed for most organs and molecules, except soluble carbohydrates in fully developed leaves whose concentration was not influenced. Among the organs, developing leaves showed the highest concentrations of secondary compounds and were the most responsive to C:N variations. Neither the biochemical nature of the compounds (C-based or N- containing metabolites) nor the calculation mode of C:N, influenced the patterns observed. Within the range of N availabilities considered (up to N limitation but not deficiency), the C:N can be considered as a good indicator of the secondary compounds concentrations in organs, especially for those involved in the chemical defence.