Impact of Moderate Cold and Salt Stress on the Accumulation of Antioxidant Flavonoids in the Leaves of Two Capsicum Cultivars.

The horticultural production of bell peppers generates large quantities of residual biomass. Abiotic stress stimulates the production of protective flavonoids, so the deliberate application of stress to the plants after fruit harvest could provide a strategy to valorize horticultural residuals by increasing flavonoid concentrations, facilitating their industrial extraction. Here we exposed two Capsicum cultivars, a chilli and a bell pepper, to cold and salt stress and combinations thereof to determine their valorization potential. Noninvasive image-based phenotyping and multiparametric fluorescence measurements indicated that all stress treatments inhibited plant growth and reduced the leaf chlorophyll fluorescence index, with the chilli cultivar showing greater sensitivity. The fluorescence-based FLAV index allowed the noninvasive assessment of foliar luteolin glycosides. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis showed that moderate cold increased the levels of two foliar antioxidant luteolin glycosides in both cultivars, with bell pepper containing the highest amounts (induced to maximum 5.5 mg g-1 DW cynaroside and 37.0 mg g-1 DW graveobioside A) after combined stress treatment. These data confirm the potential of abiotic stress for the valorization of residual leaf biomass to enhance the industrial extraction of antioxidant and bioactive flavonoids.

How to make a tumour: cell type specific dissection of Ustilago maydis-induced tumour development in maize leaves.

The biotrophic fungus Ustilago maydis causes smut disease on maize (Zea mays), which is characterized by immense plant tumours. To establish disease and reprogram organ primordia to tumours, U. maydis deploys effector proteins in an organ-specific manner. However, the cellular contribution to leaf tumours remains unknown. We investigated leaf tumour formation at the tissue- and cell type-specific levels. Cytology and metabolite analysis were deployed to understand the cellular basis for tumourigenesis. Laser-capture microdissection was performed to gain a cell type-specific transcriptome of U. maydis during tumour formation. In vivo visualization of plant DNA synthesis identified bundle sheath cells as the origin of hyperplasic tumour cells, while mesophyll cells become hypertrophic tumour cells. Cell type-specific transcriptome profiling of U. maydis revealed tailored expression of fungal effector genes. Moreover, U. maydis See1 was identified as the first cell type-specific fungal effector, being required for induction of cell cycle reactivation in bundle sheath cells. Identification of distinct cellular mechanisms in two different leaf cell types and of See1 as an effector for induction of proliferation of bundle sheath cells are major steps in understanding U. maydis-induced tumour formation. Moreover, the cell type-specific U. maydis transcriptome data are a valuable resource to the scientific community.

Leaf wounding or simulated herbivory in young N. attenuata plants reduces carbon delivery to roots and root tips.

MAIN CONCLUSION: In Nicotiana attenuata seedlings, simulated herbivo ry by the specialist Manduca sexta decreases root growth and partitioning of recent photoassimilates to roots in contrast to increased partitioning reported for older plants. Root elongation rate in Nicotiana attenuata has been shown to decrease after leaf herbivory, despite reports of an increased proportion of recently mobilized photoassimilate being delivered towards the root system in many species after similar treatments. To study this apparent contradiction, we measured the distribution of recent photoassimilate within root tissues after wounding or simulated herbivory of N. attenuata leaves. We found no contradiction: herbivory reduced carbon delivery to root tips. However, the speed of phloem transport in both shoot and root, and the delivery of recently assimilated carbon to the entire root system, declined after wounding or simulated herbivory, in contrast with the often-reported increase in root partitioning. We conclude that the herbivory response in N. attenuata seedlings is to favor the shoot and not bunker carbon in the root system.

Long-term persistence of various 14C-labeled pesticides in soils.

The fate of the 14C-labeled herbicides ethidimuron (ETD), methabenzthiazuron (MBT), and the fungicide anilazine (ANI) in soils was evaluated after long-term aging (9-17 years) in field based lysimeters subject to crop rotation. Analysis of residual 14C activity in the soils revealed 19% (ETD soil; 0-10 cm depth), 35% (MBT soil; 0-30), and 43% (ANI soil; 0-30) of the total initially applied. Accelerated solvent extraction yielded 90% (ETD soil), 26% (MBT soil), and 41% (ANI soil) of residual pesticide 14C activity in the samples. LC-MS/MS analysis revealed the parent compounds ETD and MBT, accounting for 3% and 2% of applied active ingredient in the soil layer, as well as dihydroxy-anilazine as the primary ANI metabolite. The results for ETD and MBT were matching with values obtained from samples of a 12 year old field plot experiment. The data demonstrate the long-term persistence of these pesticides in soils based on outdoor trials.

Analysis of alkaloids in single plant cells by capillary electrophoresis.

In this chapter, capillary electrophoresis (CE) is demonstrated to be a useful technique for the determination of alkaloids in microsamples of single plant cells. A single cell sampling technique with microcapillaries that includes extraction of sample volumes in the pl range from single cells, division into aliquots, addition of internal standard, and injection into the CE capillary is described. The danger of contamination and evaporation of such low sample volumes has been avoided by handling them under an inert protective layer of silicone oil. For the determination of alkaloids in cell samples, CE with direct ultraviolet detection using a high concentration of citric acid as background electrolyte provides sufficient sensitivity.