Cysteine-rich receptor-like kinases (CRKs) are transmembrane proteins characterized by the presence of two domains of unknown function 26 (DUF26) in their ectodomain. The CRKs form one of the largest groups of receptor-like protein kinases in plants, but their biological functions have so far remained largely uncharacterized. We conducted a large-scale phenotyping approach of a nearly complete crk T-DNA insertion line collection showing that CRKs control important aspects of plant development and stress adaptation in response to biotic and abiotic stimuli in a non-redundant fashion. In particular, the analysis of reactive oxygen species (ROS)-related stress responses, such as regulation of the stomatal aperture, suggests that CRKs participate in ROS/redox signalling and sensing. CRKs play general and fine-tuning roles in the regulation of stomatal closure induced by microbial and abiotic cues. Despite their great number and high similarity, large-scale phenotyping identified specific functions in diverse processes for many CRKs and indicated that CRK2 and CRK5 play predominant roles in growth regulation and stress adaptation, respectively. As a whole, the CRKs contribute to specificity in ROS signalling. Individual CRKs control distinct responses in an antagonistic fashion suggesting future potential for using CRKs in genetic approaches to improve plant performance and stress tolerance.

This study aimed to understand the molecular mechanisms of nitrogen dioxide (NO)-induced toxicity and cell death in plants. Exposure of Arabidopsis to high concentrations of NO induced cell death in a dose-dependent manner. No leaf symptoms were visible after fumigation for 1 h with 10 parts per million (ppm) NO However, 20 ppm NO caused necrotic lesion formation and 30 ppm NO complete leaf collapse, which had already started during the 1 h fumigation period. NO fumigation resulted in a massive accumulation of nitrite and in protein modifications by S-nitrosylation and tyrosine nitration. Nitric oxide (NO) at 30 ppm did not trigger leaf damage or any of the effects observed after NO fumigation. The onset of NO-induced cell death correlated with NO and hydrogen peroxide (HO) signaling and a decrease in antioxidants. NO- and HO-accumulating mutants were more sensitive to NO than wild-type plants. Accordingly, experiments with specific scavengers confirmed that NO and HO are essential promoters of NO-induced cell death. Leaf injection of 100 mM nitrite caused an increase in S-nitrosylation, NO, HO, and cell death suggesting that nitrite functioned as a mediator of NO-induced effects. A targeted screening of phytohormone mutants revealed a protective role of salicylic acid (SA) signaling in response to NO It was also shown that phytohormones were modulators rather than inducers of NO-induced cell death. The established experimental set-up is a suitable system to investigate NO and cell death signaling in large-scale mutant screens.

Nitric oxide (NO) is an important signalling molecule that is involved in many different physiological processes in plants.Here, we report about a NO-fixing mechanism in Arabidopsis, which allows the fixation of atmospheric NO into nitrogen metabolism. We fumigated Arabidopsis plants cultivated in soil or as hydroponic cultures during the whole growing period with up to 3 ppmv of NO gas. Transcriptomic, proteomic and metabolomic analyses were used to identify non-symbiotic haemoglobin proteins as key components of the NO-fixing process. Overexpressing non-symbiotic haemoglobin 1 or 2 genes resulted in fourfold higher nitrate levels in these plants compared with NO-treated wild-type. Correspondingly, rosettes size and weight, vegetative shoot thickness and seed yield were 25, 40, 30, and 50% higher, respectively, than in wild-type plants. Fumigation with 250 ppbv 15 NO confirmed the importance of non-symbiotic haemoglobin 1 and 2 for the NO-fixation pathway, and we calculated a daily uptake for non-symbiotic haemoglobin 2 overexpressing plants of 250 mg N/kg dry weight. This mechanism is probably important under conditions with limited N supply via the soil. Moreover, the plant-based NO uptake lowers the concentration of insanitary atmospheric NOx, and in this context, NO-fixation can be beneficial to air quality.

A lysimeter study was performed to monitor effects of elevated ozone on juvenile trees of Fagus sylvatica L. as well as on the plant-soil system. During a fumigation period over almost three growing seasons, parameters related to plant growth, phenological development and physiology as well as soil functions were studied. The data analyses identified elevated ozone to delay leaf phenology at early and to accelerate it at late developmental stages, to reduce growth, some leaf nutrients (Ca, K) as well as some soluble phenolics (hydroxycinnamic acid derivatives, total flavonol glycosides). No or very weak ozone effects were found in mobile carbon pools of leaves (starch, sucrose), and other phenolic compounds (flavans). Altered gene expression related to stress and carbon cycling corresponded well with findings from leaf phenology and chemical composition analyses indicating earlier senescence and oxidative stress in leaves under elevated ozone. Conversely in the soil system, no effects of ozone were detected on soil enzyme activities, rates of litter degradation and lysimeter water balances. Despite the fact that the three reported years 2003-2005 were climatically very contrasting including a hot and dry as well as an extremely wet summer, and also mild as well as cold winters, the influence of ozone on a number of plant parameters is Water Air Soil Pollut: Focus (

A continuous labelling approach to recover photosynthetically fixed carbon in plant tissue and rhizosphere organisms of young beech trees (Fagus sylvatica L.) using 13 C depleted CO 2 Abstract A continuous labelling experiment using 13 C-CO 2 was set up in open-top chambers in order to follow fluxes of assimilates from the plant into the rhizosphere. Labelling was performed for one growing season by adding low amounts of CO 2 depleted in 13 C to the atmosphere of the open-top chambers, resulting in a difference of Δ 13 C 5‰ V-PDB compared to ambient conditions. The label was recovered in both plant parts and soil microbial communities, analysed via phospholipid fatty acid (PLFA) side chains. PLFA 18:2ω6,9 showed a significant incorporation of the 13 C label in October, indicating that fungi utilized plant derived carbon. In bacterial PLFA no label incorporation was detected, probably due to a lower use of rhizodeposits or a preference to older carbon compounds as energy sources. This experimental setup represents a low-cost continuous labelling method for field experiments with only minor increase of CO 2 concentrations.