Drought is one of the major stress factors affecting the growth and development of plants. In this context, drought-related losses of crop plant productivity impede sustainable agriculture all over the world. In general, plants respond to water deficits by multiple physiological and metabolic adaptations at the molecular, cellular, and organism levels. To understand the underlying mechanisms of drought tolerance, adequate stress models and arrays of reliable stress markers are required. Therefore, in this review we comprehensively address currently available models of drought stress, based on culturing plants in soil, hydroponically, or in agar culture, and critically discuss advantages and limitations of each design. We also address the methodology of drought stress characterization and discuss it in the context of real experimental approaches. Further, we highlight the trends of methodological developments in drought stress research, i.e., complementing conventional tests with quantification of phytohormones and reactive oxygen species (ROS), measuring antioxidant enzyme activities, and comprehensively profiling transcriptome, proteome, and metabolome.

Nitrogen fixation is an agronomically and environmentally important process catalyzed by bacterial nitrogenase within legume root nodules. These unique symbiotic organs have high metabolic rates and produce large amounts of reactive oxygen species that may modify proteins irreversibly. Here, we examined two types of oxidative posttranslational modifications of nodule proteins: carbonylation, which occurs by direct oxidation of certain amino acids or by interaction with reactive aldehydes arising from cell membrane lipid peroxides; and glycation, which results from the reaction of lysine and arginine residues with reducing sugars or their autooxidation products. We used a strategy based on the enrichment of carbonylated peptides by affinity chromatography followed by liquid chromatography-tandem mass spectrometry to identify 369 oxidized proteins in bean () nodules. Of these, 238 corresponded to plant proteins and 131 to bacterial proteins. Lipid peroxidation products induced most carbonylation sites. This study also revealed that carbonylation has major effects on two key nodule proteins. Metal-catalyzed oxidation caused the inactivation of malate dehydrogenase and the aggregation of leghemoglobin. In addition, numerous glycated proteins were identified in vivo, including three key nodule proteins: sucrose synthase, glutamine synthetase, and glutamate synthase. Label-free quantification identified 10 plant proteins and 18 bacterial proteins as age-specifically glycated. Overall, our results suggest that the selective carbonylation or glycation of crucial proteins involved in nitrogen metabolism, transcriptional regulation, and signaling may constitute a mechanism to control cell metabolism and nodule senescence.

Due to low culturing costs and high seed protein contents, legumes represent the main global source of food protein. Pea (Pisum sativum L.) is one of the major legume crops, impacting both animal feed and human nutrition. Therefore, the quality of pea seeds needs to be ensured in the context of sustainable crop production and nutritional efficiency. Apparently, changes in seed protein patterns might directly affect both of these aspects. Thus, here, we address the pea seed proteome in detail and provide, to the best of our knowledge, the most comprehensive annotation of the functions and intracellular localization of pea seed proteins. To address possible intercultivar differences, we compared seed proteomes of yellow- and green-seeded pea cultivars in a comprehensive case study. The analysis revealed totally 1938 and 1989 nonredundant proteins, respectively. Only 35 and 44 proteins, respectively, could be additionally identified after protamine sulfate precipitation (PSP), potentially indicating the high efficiency of our experimental workflow. Totally 981 protein groups were assigned to 34 functional classes, which were to a large extent differentially represented in yellow and green seeds. Closer analysis of these differences by processing of the data in KEGG and String databases revealed their possible relation to a higher metabolic status and reduced longevity of green seeds.

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Due to the oncoming climate changes water deficit represents one of the most important abiotic stressors which dramatically affects crop productivity worldwide. Because of their importance as the principal source of food protein, legumes attract a special interest of plant scientists. Moreover, legumes are involved in symbiotic association with rhizobial bacteria, which is morphologically localized to root nodules. These structures are critical for fixation of atmospheric nitrogen and highly sensitive to drought. Therefore, new drought-tolerant legume cultivars need to be developed to meet the growing food demand. However, this requires a comprehensive knowledge of the molecular mechanisms behind the plant stress response. To access these mechanisms, adequate and reliable drought stress models need to be established. The agar-based polyethylene glycol (PEG) infusion model allows a physiologically relevant reduction of soil water potential (Ψw), although it is restricted to seedlings and does not give access to proteomics and metabolomics studies. Earlier, we successfully overcame this limitation and optimized this model for mature Arabidopsis plants. Here we make the next step forward and address its application to one of the major crop legumes — pea. Using a broad panel of physiological and biochemical markers, we comprehensively prove the applicability of this setup to legumes. The patterns of drought-related physiological changes are well-interpretable and generally resemble the stress response of plants grown in soil-based stop-watering models. Thus, the proposed model can be efficiently used in the study of stress-related metabolic adjustment in green parts, roots and root nodules of juvenile and flowering plants.