Tomato is one of the most produced crop plants on earth and growing in the fields and greenhouses all over the world. Breeding with known traits of wild species can enhance stress tolerance of cultivated crops. In this study, we investigated responses of the transcriptome as well as primary and secondary metabolites in leaves of a cultivated and a wild tomato to several abiotic stresses such as nitrogen deficiency, chilling or warmer temperatures, elevated light intensities and combinations thereof. The wild species responded different to varied temperature conditions compared to the cultivated tomato. Nitrogen deficiency caused the strongest responses and induced in particular the secondary metabolism in both species but to much higher extent in the cultivated tomato. Our study supports the potential of a targeted induction of valuable secondary metabolites in green residues of horticultural production, that will otherwise only be composted after fruit harvest. In particular, the cultivated tomato showed a strong induction in the group of mono caffeoylquinic acids in response to nitrogen deficiency. In addition, the observed differences in stress responses between cultivated and wild tomato can lead to new breeding targets for better stress tolerance.

The plant kingdom contains an enormous diversity of bioactive compounds which regulate plant growth and defends against biotic and abiotic stress. Some of these compounds, like flavonoids, have properties which are health supporting and relevant for industrial use. Many of these valuable compounds are synthesized in various pepper (Capsicum sp.) tissues. Further, a huge amount of biomass residual remains from pepper production after harvest, which provides an important opportunity to extract these metabolites and optimize the utilization of crops. Moreover, abiotic stresses induce the synthesis of such metabolites as a defense mechanism. Two different Capsicum species were therefore exposed to chilling temperature (24/18 ℃ vs. 18/12 ℃), to salinity (200 mM NaCl), or a combination thereof for 1, 7 and 14 days to investigate the effect of these stresses on the metabolome and transcriptome profiles of their leaves. Both profiles in both species responded to all stresses with an increase over time. All stresses resulted in repression of photosynthesis genes. Stress involving chilling temperature induced secondary metabolism whereas stresses involving salt repressed cell wall modification and solute transport. The metabolome analysis annotated putatively many health stimulating flavonoids (apigetrin, rutin, kaempferol, luteolin and quercetin) in the Capsicum biomass residuals, which were induced in response to salinity, chilling temperature or a combination thereof, and supported by related structural genes of the secondary metabolism in the network analysis.

Main conclusion: This study investigates the capability of leaf reflectance measurements to identify stress responses under combined stress treatment. Crops are subjected to various environmental stresses, mostly occurring in combination. Research on combined stresses is important, but most studies focus on single stresses. We analyzed physiological responses of two Capsicum species to single cold and salt stresses, which differ from the responses to combinations of these stresses. Combined stress caused growth to decrease more than individual stresses. Single cold stress significantly reduced photosynthetic pigments in both species. However, single salt stress increased pigments in C. annuum . Under combined stress, photosynthetic pigments were decreased to a lower extent compared to single cold stress. An increase in leaf reflectance around 550 nm and a significant shift in the red-edge peak of the first derivative corresponded with chlorophyll content. The effects of single cold and combined stress were similar, differing only in magnitude. Only C. chinense showed a response in leaf reflectance to salt stress. Spectral vegetation indices distinguished single cold from single salt stress, whereas the effects of single cold and the combined stress were similar, indicating a dominating effect of cold stress. The photochemical reflectance index (PRI), however, distinguished between all three treatments. This research confirms that the responses to combined stresses are unique and different from responses to individual stresses. A strong effect of one stress can mask another. This can lead to misinterpretation when combined stresses occur. The use of hyperspectral signals for quantification of responses to combined stresses must be carefully evaluated and established for further research to assist breeding of climate-resilient crops performing well under multi-stress events.

Tomato is one of the most produced crop plants on earth and growing in the fields and greenhouses all over the world. Breeding with known traits of wild species can enhance stress tolerance of cultivated crops. In this study, we investigated responses of the transcriptome as well as primary and secondary metabolites in leaves of a cultivated and a wild tomato to several abiotic stresses such as nitrogen deficiency, chilling or warmer temperatures, elevated light intensities and combinations thereof. The wild species responded different to varied temperature conditions compared to the cultivated tomato. Nitrogen deficiency caused the strongest responses and induced in particular the secondary metabolism in both species but to much higher extent in the cultivated tomato. Our study supports the potential of a targeted induction of valuable secondary metabolites in green residues of horticultural production, that will otherwise only be composted after fruit harvest. In particular, the cultivated tomato showed a strong induction in the group of mono caffeoylquinic acids in response to nitrogen deficiency. In addition, the observed differences in stress responses between cultivated and wild tomato can lead to new breeding targets for better stress tolerance.

Background: Potato flowers and berries are largely unused agricultural side-streams that may provide bioactive compounds for pharmaceutical and plant protection applications in a circular bioeconomy. This study evaluated their potential as sources of secondary metabolites and assessed whether premature harvesting affects final tuber yield. Methods: Field trials with two potato cultivars were combined with targeted HPLC-MS/MS analysis, untargeted metabolomics, and RNA-Seq analysis of flowers and developing berries. Results: Berries produced substantially more biomass than flowers, whereas flowers generally contained higher concentrations of total glycoalkaloids (calculated as the sum of a-solanine and a-chaconine). This reached 393.95 mg/100 g FW in ‘Quarta’ flowers compared to 70.92 mg/100 g FW in berries, with the concentration of a-chaconine up to 3.33-fold higher than that of a-solanine. Untargeted metabolomics identified glycoalkaloids, phenolic compounds, and other secondary metabolites, with peak intensities of rutin and some others declining from ~1Å~10 ⁹ to ~1Å~10 ⁵ during berry development. Transcriptomic analysis showed that tissue and developmental stage had a substantially greater influence on gene expression patterns than cultivar. Genes associated with phenylpropanoid, terpenoid and steroid-related pathways were differentially expressed, with overall stronger upregulation in flowers than in small and big berries. Premature flower harvest did not reduce tuber yield, whereas berry harvest reduced yield for one cultivar in one field experiment. Conclusion: Overall, flowers and berries harvested as side streams in the potato production can be a good source for glycoalkaloids and possibly further metabolites of use for pharmaceutical and plant protection applications. Flowers appear particularly suitable for recovering high-concentration bioactive compounds, whereas berries offer advantages in biomass availability, harvesting, and storage.